Xiaolu Wang, Yu Wang, Jiao Liu et al.

Bioresources and Bioprocessing • 2017

BackgroundMethanol is regarded as a biorenewable platform feedstock because nearly all bioresources can be converted into methanol through syngas. Biological conversion of methanol using synthetic methylotrophs has thus gained worldwide attention.ResultsHerein, to endow Escherichia coli with the ability to utilize methanol, an artificial linear methanol assimilation pathway was assembled in vivo for the first time. Distinct from native cyclic methanol utilization pathways, such as ribulose monophosphate cycle, the linear pathway requires no formaldehyde acceptor and only consists of two enzymatic reactions: oxidation of methanol into formaldehyde by methanol dehydrogenase and carboligation of formaldehyde into dihydroxyacetone by formolase. After pathway engineering, genome replication engineering assisted continuous evolution was applied to improve methanol utilization. 13C-methanol-labeling experiments showed that the engineered and evolved E. coli assimilated methanol into biomass.ConclusionsThis study demonstrates the usability of the linear methanol assimilation pathway in bioconversion of C1 resources such as methanol and methane.

Jonas A. Ohlsson, A. Harman-Ware, M. Sandgren et al.

BioEnergy Research • 2019

Biomass recalcitrance, the inherent resistance of plants towards deconstruction, negatively affects the viability of biorefineries. This trait is not only dictated by the properties of the biomass but also by the conversion system used and its interactions with specific features of the biomass. Here, biomass recalcitrance to anaerobic digestion (AD) was assessed using a biomethanation potential (BMP) assay. Plant material ( n = 94) was selected from a large population of natural Salix viminalis accessions, previously evaluated for biomass recalcitrance using hydrothermal pretreatment–enzymatic hydrolysis. Correlations between yields from the two biological conversion systems were evaluated, as well as the influence of biomass compositional features, analyzed by pyrolysis-molecular beam mass spectrometry (py-MBMS), and other biomass physical properties on conversion performance. BMP values averaged 198.0 Nml CH 4 /g biomass after 94 days, ranging from 28.6 to 245.9. S lignin and carbohydrate-derived spectral features were positively correlated with performance under both systems, whereas G lignin, p -coumaric acid, and ferulic acid-derived ions were negatively correlated with yields and rates. Most spectral features were more strongly correlated with enzymatic hydrolysis yields compared to methane production. For early-stage methane production and rate, recalcitrance factors were similar compared to enzymatic hydrolysis, with weaker correlations observed at later timepoints. The results suggest that although variation in methane potential was considerably lower than enzymatic hydrolysis yields, a reduced recalcitrance under this system will still be of importance to improve early conversion rates. Spectral features of low methane-producing samples indicate the presence of inhibitory substances, warranting further study.

R. Kumar, S. Bhagia, M. Smith et al.

Green Chemistry • 2018

It has been previously shown that cellulose-lignin droplets’ strong interactions, resulting from lignin coalescence and redisposition on cellulose surface during thermochemical pretreatments, increase cellulose recalcitrance to biological conversion, especially at commercially viable low enzyme loadings. However, information on the impact of cellulose–hemicellulose interactions on cellulose recalcitrance following relevant pretreatment conditions are scarce. Here, to investigate the effects of plausible hemicellulose precipitation and re-association with cellulose on cellulose conversion, different pretreatments were applied to pure Avicel® PH101 cellulose alone and Avicel mixed with model hemicellulose compounds followed by enzymatic hydrolysis of resulting solids at both low and high enzyme loadings. Solids produced by pretreatment of Avicel mixed with hemicelluloses (AMH) were found to contain about 2 to 14.6% of exogenous, precipitated hemicelluloses and showed a remarkably much lower digestibility (up to 60%) than their respective controls. However, the exogenous hemicellulosic residues that associated with Avicel following high temperature pretreatments resulted in greater losses in cellulose conversion than those formed at low temperatures, suggesting that temperature plays a strong role in the strength of cellulose–hemicellulose association. Molecular dynamics simulations of hemicellulosic xylan and cellulose were found to further support this temperature effect as the xylan–cellulose interactions were found to substantially increase at elevated temperatures. Furthermore, exogenous, precipitated hemicelluloses in pretreated AMH solids resulted in a larger drop in cellulose conversion than the delignified lignocellulosic biomass containing comparably much higher natural hemicellulose amounts. Increased cellulase loadings or supplementation of cellulase with xylanases enhanced cellulose conversion for most pretreated AMH solids; however, this approach was less effective for solids containing mannan polysaccharides, suggesting stronger association of cellulose with (hetero) mannans or lack of enzymes in the mixture required to hydrolyze such polysaccharides.

Nawa Raj Baral, Eric Sundstrom, Lalitendu Das et al.

ACS Sustainable Chemistry & Engineering • 2019

The future bioeconomy promises drop-in or performance-advantaged biofuels and bioproducts derived from lignocellulosic biomass, substantial greenhouse gas emissions reductions in sectors with few or no alternatives, and increased domestic energy production in countries with sufficient biomass resources. Despite the slower than anticipated pace of commercializing next-generation biofuels, the research community continues to make dramatic improvements at every stage of production, from feedstock cultivation through conversion to final products. However, the interdisciplinary nature of bioenergy research, and the need for cross-coordination among biologists, chemists, agronomists, and engineers, make coordinating and optimizing these strategies challenging. This Perspective surveys recent advancements in bioenergy crop engineering, lignocellulosic biomass deconstruction and fractionation, catabolism of biomass-derived sugars and aromatics, and biological conversion to fuels and products. We organize major re...

Xu Wei, J. Pandohee, Baojun Xu

Critical Reviews in Food Science and Nutrition • 2023

Abstract This review elaborates on biochemical characteristics, in vivo metabolism, biological conversion through UV irradiation, as well as dietary fortification of vitamin D. Recent innovations in vitamin D utilization, including nanoencapsulation, direct or indirect addition, emulsion, ultrasound, microwave processing, CRISPR-Cas9 genome editing, as well as UV photoconversion, were summarized. Mushrooms, eggs, yeasts, as well as seafood, such as Barramundi and Atlantic salmon, were typical representatives of original natural food materials for vitamin D bioconversion in relevant research. The critical session thereof referred to the 295 nm UV-B irradiation triggering biological fortification of vitamin D2 and vitamin D3, which occurred in ergosterol from mushrooms, and cholesterol from egg yolk, respectively. The schematic biosynthesis of vitamin D precursors in yeasts regulated miscellaneous enzymes were clearly demonstrated. These summarized pathways played a role as a theoretical primer for vitamin D bioconversion when the UV irradiation technique is concerned. Besides, tomatoes had become the latest potential vitamin D sources after genetic modification. The safety consideration for vitamin D fortified functional food was discussed either. Further research is required to fill the gap of investigating optimized factors like types of eggs, meat, and grain, boarder range of wavelength, and dosage in UV irradiation. Vitamin D has a great potential market in the field of functional food development.

Stetson S. Bassett, Eva C. Nieminski, David K. Stevens

AWWA Water Science • 2019

The purpose of this study was to evaluate water quality and operational trends of a side‐by‐side, full‐scale biofiltration conversion. Four filters at a water treatment plant, treating low turbidity and low total organic carbon water, were monitored for one year. One filter was a prechlorinated control, and the other three were biofilters. One was a standard biofilter, one had chlorinated backwash, and the third was supplemented with nutrients. Slightly higher concentrations of adenosine triphosphate (ATP) (175–2,300 ng ATP/cm 3 ) and extracellular polymeric substances (0.00–0.08 mg glucose/g total solids) were found in the biofilters compared with the control. Total trihalomethanes and haloacetic acid were lower in the biofilters relative to the control (60 and 30%, respectively). Conversion to biological filtration resulted in slightly higher (0.019 ntu) and more variable (0.013 ntu) effluent turbidity, but filter run volumes were unaffected. At the conclusion of the study, a decision was made to convert all the filters in the plant to biofilters.

Agampodi Sunil Shanta Mendis, Shashiprabha Punyakantha Dunuweera, Shanta Walpolage et al.

Detritus • 2020

Conversion of the sludge generated in the biological treatment plants of glove dipping industries of Sri Lanka to a valuable organic fertilizer after removing toxic metal ions such as heavy metals and excess Zn and Al present in the sludge to allowable limits is described. In order to do so, the raw materials used were analysed for these species and for their nutritional values. Removal of metal ions by different acids such as HNO3 and acetic acid digestion processes are revealed and the results are compared. Dilution of the metal ion-removed sludge with other raw materials used in organic fertilizer production to enable maintain right C:N ratio and the use of these materials in the fertilizer production process used are presented. Application of the fertilizer to soils of fruit and vegetable plantations and measurement of Zn, Al and heavy metals in the soil and plant parts and their crops as a function of time is also described. The quality of vegetables and fruits produced by applying this new fertilizer is compared with those obtained in the open market.It has been shown that the former contains no or much less than maximum allowable limits of heavy metals or toxic species when compared to those grown using other organic fertilizers. This study is useful for industrial biological treatment plant sludge management by converting it to a useful product.

Jinwoo Yang, Junsoo Lee

The FASEB Journal • 2018

Flavonoids attract much attention due to their various physiological properties and these compounds naturally exist as their glycoside forms. Rutin, one of the most abundant flavonoids in nature, is composed of the aglycone quercetin and the disaccharide rutinose. Although, there is a structural similarity in rutin and quercetin, there are some obvious differences in physical, chemical, and biological characters. It is reported that quercetin has a higher biological activity than other glycosidic quercetin derivatives. Thus, de‐glycosylation of rutin would be an important process for enhanced biological activities. Therefore, in this study, to convert rutin to quercetin, the effects of acid concentrations and solvents were investigated and biological activities were evaluated. As a results, when 80 % ethanol was used, the hydrolysis of rutin was more rapid than water as solvent for reaction. Hydrolysis of rutin was also accelerated as the acid concentration increased from 0.1 to 1.0 M of HCl. Anti‐oxidant, anti‐inflammatory, and anti‐adipogenic activities were increased with the increased conversion rate of rutin to quercetin. These results suggest that the acid treatment can be used as a process to improve the physiological activity of glycoside flavonoids. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

P Timms, IC MacRae

Australian Journal of Biological Sciences • 1982

In a detailed study it was shown that washed cell suspensions of K. pneumoniae reduced the organophosphorus pesticide fensulfothion to fensulfothion sulfide. Temperature and pH optima for this conversion plus sensitivity to sulfydryl-reacting agents strongly suggested enzyme involvement. The reaction was also quite sensitive to molecular oxygen, only proceeding under conditions of low oxygen tension. Once formed, the fensulfothion sulfide was rapidly bound by living and heat-killed cells. A combination of lysozyme treatment and differential centrifugation showed 90 % of the sulfide to be concentrated in the cell membrane fraction of exposed cells.

Anke Wolthoorn, Simon Kuitert, Henk Dijkman et al.

Advanced Materials Research • 2007

In a bench scale trial biological sulfate reduction was applied to convert anglesite (PbSO4) to galena (PbS). Anglesite is a main constituent of waste fractions such as the residue from an indirect leaching process or in lead paste from spent car batteries. The goal of this study was to develop a technology to decrease the lead (Pb) emissions by converting PbSO4 from a waste fraction into PbS, which can be recovered from the waste fraction using a flotation process or an electrochemical process. The conversion of anglesite to galena is based on the biological sulfate reduction process and a metal precipitation process. First sulfate is biologically reduced to sulfide. Secondly, the Pb2+ from the PbSO4 reacts chemically with the sulfide resulting from the first reaction. A bench-scale reactor was started up using sulfate- and sulfur-containing influent. The reactor was seeded with biocatalyst from several full-scale reactors. Anglesite-containing residue was added batch-wise when the formation of sulfide started. The residue contained mainly PbSO4 (51.7%), sulfate (SO4 2-, 19.9%) and elemental sulfur (S0, 15.1%). Galena precipitates in the bioreactor due to the near-neutral pH at which sulfate reduction is carried out. During the experiment a surplus of sulfide relative to Pb was maintained to prevent the formation of PbCO3 and the accompanying pH decrease that would unavoidable result in the inhibition of the biocatalyst. Both sulfate and sulfur present in the residue were biologically reduced. The formation of PbS was confirmed by the increased Pb:O ratio of the sludge (1:0.03) relative to the Pb:O ratio of the residue (1:0.3). A potential large-scale application is proposed.

Po Min Li, Ching Wei Lee, Jhan Shan Lin

Advanced Materials Research • 2011

Lignocellulose is one of the richest biological resources on earth. Yet, due to the robust structure, lignocelluloses are still not effectively utilized. This research adopted the fungi from the nature— Corilus versicolor —to culture and destroy the lignocellusic structure. The object of the research was banana stalks, a common Taiwan agricultural waste. The banana stalks were physically pretreated to banana wood flour before use. Through changes of the grains’ sizes of the banana wood flour, and proportions of the compounded carbons of the banana wood flour in the media, the optimal degradation activity was determined. The result showed that on the 12 th day the 5mm grains used to replace the compounded carbons reached the maximal microbial activity, 70 times of a general medium. On the 14 th day near 18% of celluloses were consumed by white-rot fungi. The result has contribution to lignocellulosic structure breakdown and a great step for energy conversion in subsequent stage.

John M. Woodley

Reaction Chemistry & Engineering • 2020

Reaction engineering needs to embrace biological conversion technologies, on the road to identify more sustainable routes for chemical manufacture.

YANG WANG, SHIJIE LIU

TAPPI Journal • 2012

Woody biomass is an important alternative source for chemicals, materials, and energy. Although different routes of woody biomass conversion have been proposed in various studies, typical biochemical production processes using woody biomass feedstocks consist of four major steps: pretreatment, hydrolysis, fermentation, and separation. Pretreatment remains the most important step in biomass conversion. This paper is a review of available pretreatment technologies for woody biomass bioconversion.

Ryuji Ohue, Kei Hashimoto, Masahiro Nakamoto et al.

Journal of Innate Immunity • 2011

Recent publications report that heat shock proteins (HSPs) can endow regulatory responses to the systemic immune system when administered via the mucosal route, leading to an amelioration of atherosclerosis and allergy. However, it remains poorly understood if HSP antigens exist in the luminal contents of the gastrointestinal tract and which types of HSP induce regulatory responses. Here we addressed these problems, considering that numerous gut microflora and foods are natural sources of HSPs. SDS-PAGE and immunoblotting with the anti-HSP60 antibody demonstrated the intact and degraded forms of HSP60 mainly in appendix and large intestine of the gastrointestinal tract. No reactivity with this antibody was observed for any of the luminal contents derived from germ-free animals, suggesting gut microflora to be a source of the intestinal HSPs because of lack of HSPs in animal chow diet. GroEL, a typical member of bacterial HSP60, showed a tendency to stimulate splenocytes in germ-free mice, compared to that in conventional mice, suggesting that resident commensal bacterial GroEL may stimulate HSP-reactive T cells as regulatory cells in conventional animals. Importantly, GroEL, but not mouse-derived HSP60, caused naïve T cells to differentiate into CD4+ CD25+ Foxp3+ T cells, indicating that the production of regulatory T cells depends on the type of HSP. Thus, HSPs derived from commensal microbes can be utilized to stimulate immunoregulatory pathways for the maintenance of intestinal homeostasis.

A. W. Khan, Duncan Wall, L. van den Berg

Applied and Environmental Microbiology • 1981

A simple procedure that uses a cellulose-enriched culture started from sewage sludge was developed for producing cellulolytic enzymes and converting cellulose to acetic acid rather than CH 4 and CO 2 . In this procedure, the culture which converts cellulose to CH 4 and CO 2 was mixed with a synthetic medium and cellulose and heated to 80°C for 15 min before incubation. The end products formed were acetic acid, propionic acid, CO 2 , and traces of ethanol and H 2 . Supernatants from 6- to 10-day-old cultures contained 16 to 36 mM acetic acid. Cellulolytic enzymes in the supernatant were stable at 2°C under aerobic conditions for up to 4 weeks and had the ability to hydrolyze carboxymethyl cellulose, a microcystalline cellulose, cellobiose, xylan, and filter paper to reducing sugars.

Rahul Saxena, Sona Vasudevan, Digvijay Patil et al.

International Journal of Molecular Sciences • 2015

DnaA oligomerizes when bound to origins of chromosomal replication. Structural analysis of a truncated form of DnaA from Aquifex aeolicus has provided insight into crucial conformational differences within the AAA+ domain that are specific to the ATP- versus ADP- bound form of DnaA. In this study molecular docking of ATP and ADP onto Escherichia coli DnaA, modeled on the crystal structure of Aquifex aeolicus DnaA, reveals changes in the orientation of amino acid residues within or near the vicinity of the nucleotide-binding pocket. Upon limited proteolysis with trypsin or chymotrypsin ADP-DnaA, but not ATP-DnaA generated relatively stable proteolytic fragments of various sizes. Examined sites of limited protease susceptibility that differ between ATP-DnaA and ADP-DnaA largely reside in the amino terminal half of DnaA. The concentration of adenine nucleotide needed to induce conformational changes, as detected by these protease susceptibilities of DnaA, coincides with the conversion of an inactive bacterial origin recognition complex (bORC) to a replication efficient pre-replication complex (pre-RC) at the E. coli chromosomal origin of replication (oriC).

Larisa Lee-Cruz, David P. Edwards, Binu M. Tripathi et al.

Applied and Environmental Microbiology • 2013

ABSTRACT Tropical forests are being rapidly altered by logging and cleared for agriculture. Understanding the effects of these land use changes on soil bacteria, which constitute a large proportion of total biodiversity and perform important ecosystem functions, is a major conservation frontier. Here we studied the effects of logging history and forest conversion to oil palm plantations in Sabah, Borneo, on the soil bacterial community. We used paired-end Illumina sequencing of the 16S rRNA gene, V3 region, to compare the bacterial communities in primary, once-logged, and twice-logged forest and land converted to oil palm plantations. Bacteria were grouped into operational taxonomic units (OTUs) at the 97% similarity level, and OTU richness and local-scale α-diversity showed no difference between the various forest types and oil palm plantations. Focusing on the turnover of bacteria across space, true β-diversity was higher in oil palm plantation soil than in forest soil, whereas community dissimilarity-based metrics of β-diversity were only marginally different between habitats, suggesting that at large scales, oil palm plantation soil could have higher overall γ-diversity than forest soil, driven by a slightly more heterogeneous community across space. Clearance of primary and logged forest for oil palm plantations did, however, significantly impact the composition of soil bacterial communities, reflecting in part the loss of some forest bacteria, whereas primary and logged forests did not differ in composition. Overall, our results suggest that the soil bacteria of tropical forest are to some extent resilient or resistant to logging but that the impacts of forest conversion to oil palm plantations are more severe.

Yuxi Liu, Jie Li, Junna Feng et al.

Journal Of Plant Ecology • 2025

Abstract Due to large-scale commercial logging and prolonged anthropogenic disturbances over the past decades, large tropical secondary forests have been converted into rubber plantations, which have substantial impacts on soil bacterial community via altering soil properties. However, how forest conversion affect soil bacterial community composition and diversity are still poorly understood. To address this, we compared the soil bacterial communities and physicochemical properties between typical secondary forests (SF) and rubber plantations (RP) in Hainan Island. The results showed that SF exhibited higher soil organic matter, total nitrogen, total carbon and pH compared to RP, particularly in the 0-10 cm layer. Besides, the soil bulk density in SF was lower than that in RP. The bacterial community composition and microbial networks were significantly varied between SF and RP. The dominant soil bacterial phyla in SF were Proteobacteria (27.37%–28.66%), followed by Acidobacteria (18.97%–19.82%), while Chloroflexi prevailed in RP (27.89%–28.45%), followed by Acidobacteria (20.93%–24.38%). Furthermore, SF exhibited more complex microbial networks owing to its higher edges, degree and links compared to RP. Meanwhile, bacterial community assembly in SF was primarily governed by deterministic processes, while stochastic processes dominated RP. The soil bacterial α-diversity in SF was higher than that in RP, which was primarily dominated by pH. Our findings demonstrate that converting secondary forests to rubber plantations does not favor soil microbial diversity and stability, as it decreases soil pH, which suggests that sustainable management strategies should prevent soil acidification in rubber plantations.

Siti Hasnawati Jamal, Nursyafiqah Jori Roslan, Noor Aisyah Ahmad Shah et al.

Solid State Phenomena • 2021

Cellulose nitrate has attracted great interest amongst researchers due to its uses in wide range of products including paint and gun propellant. Therefore, this work focuses on the synthesis of cellulose nitrate from two different sources of cellulose; plant and bacterial, in order to obtain high percentage of nitrogen content hence suitable for propellant application. The synthesis of cellulose nitrate was carried out via nitration method using nata de coco and kapok ( Ceiba pentadra L ) as a raw materials of cellulose. The samples were then characterized by elemental analysis, fourier transform infrared (FTIR) spectroscopy, x-ray diffraction and surface electron morphology (SEM). FTIR analysis showed the presence of NO 2 groups in both nitrocellulose proving that nitrocellulose was successfully synthesized by nitration method even though it was produced from different sources of cellulose. It is also showed nitrocellulose with high percentage of nitrogen content was obtained from bacterial cellulose, 12.69% rather than plant cellulose.

Lloyd J. Nadeau, Zhongqi He, Jim C. Spain

Applied and Environmental Microbiology • 2003

ABSTRACT Hydroxylamino aromatic compounds are converted to either the corresponding aminophenols or protocatechuate during the bacterial degradation of nitroaromatic compounds. The origin of the hydroxyl group of the products could be the substrate itself (intramolecular transfer mechanism) or the solvent water (intermolecular transfer mechanism). The conversion of hydroxylaminobenzene to 2-aminophenol catalyzed by a mutase from Pseudomonas pseudoalcaligenes JS45 proceeds by an intramolecular hydroxyl transfer. The conversions of hydroxylaminobenzene to 2- and 4-aminophenol by a mutase from Ralstonia eutropha JMP134 and to 4-hydroxylaminobenzoate to protocatechuate by a lyase from Comamonas acidovorans NBA-10 and Pseudomonas sp. strain 4NT were proposed, but not experimentally proved, to proceed by the intermolecular transfer mechanism. GC-MS analysis of the reaction products formed in H 2 18 O did not indicate any 18 O-label incorporation during the conversion of hydroxylaminobenzene to 2- and 4-aminophenols catalyzed by the mutase from R. eutropha JMP134. During the conversion of 4-hydroxylaminobenzoate catalyzed by the hydroxylaminolyase from Pseudomonas sp. strain 4NT, only one of the two hydroxyl groups in the product, protocatechuate, was 18 O labeled. The other hydroxyl group in the product must have come from the substrate. The mutase in strain JS45 converted 4-hydroxylaminobenzoate to 4-amino-3-hydroxybenzoate, and the lyase in Pseudomonas strain 4NT converted hydroxylaminobenzene to aniline and 2-aminophenol but not to catechol. The results indicate that all three types of enzyme-catalyzed rearrangements of hydroxylamino aromatic compounds proceed via intramolecular transfer of hydroxyl groups.

Alberto Rodriguez, Jamie A. Meadows, Ning Sun et al.

Microbial Cell Factories • 2021

Abstract Hydroxycinnamic acids such as p -coumaric acid (CA) are chemically linked to lignin in grassy biomass with fairly labile ester bonds and therefore represent a straightforward opportunity to extract and valorize lignin components. In this work, we investigated the enzymatic conversion of CA extracted from lignocellulose to 4-vinylphenol (4VP) by expressing a microbial phenolic acid decarboxylase in Corynebacterium glutamicum , Escherichia coli, and Bacillus subtilis . The performance of the recombinant strains was evaluated in response to the substrate concentration in rich medium or a lignin liquor and the addition of an organic overlay to perform a continuous product extraction in batch cultures. We found that using undecanol as an overlay enhanced the 4VP titers under high substrate concentrations, while extracting > 97% of the product from the aqueous phase. C. glutamicum showed the highest tolerance to CA and resulted in the accumulation of up to 187 g/L of 4VP from pure CA in the overlay with a 90% yield when using rich media, or 17 g/L of 4VP with a 73% yield from CA extracted from lignin. These results indicate that C. glutamicum is a suitable host for the high-level production of 4VP and that further bioprocess engineering strategies should be explored to optimize the production, extraction, and purification of 4VP from lignin with this organism.

H. L. Sadoff, Emel Celikkol, H. L. Engelbrecht

Proceedings of the National Academy of Sciences • 1970

A protease is elaborated by cells of Bacillus cereus during sporulation. This sporulation-specific enzyme, in a limited proteolysis, converts vegetative cell aldolase to spore aldolase.

Alejandra Calvo-Díaz, Xosé Anxelu G. Morán

Applied and Environmental Microbiology • 2009

ABSTRACT Leucine-to-carbon conversion factors (CFs) are needed for converting substrate incorporation into biomass production of heterotrophic bacteria. During 2006 we performed 20 dilution experiments for determining the spatiotemporal variability of empirical CFs in temperate Atlantic coastal waters. Values (0.49 to 1.92 kg C mol Leu −1 ) showed maxima in autumn to early winter and minima in summer. Spatially averaged CFs were significantly negatively correlated with in situ leucine incorporation rates ( r = −0.91) and positively correlated with phosphate concentrations ( r = 0.76). These relationships, together with a strong positive covariation between cell-specific leucine incorporation rates and carbon contents ( r = 0.85), were interpreted as a strategy to maximize survival through protein synthesis and low growth rates under nutrient limitation (low CFs) until favorable conditions stimulate cell division relative to protein synthesis (high CFs). A multiple regression with in situ leucine incorporation rates and cellular carbon contents explained 96% of CF variance in our ecosystem, suggesting their potential prediction from more easily measurable routine variables. The use of the theoretical CF of 1.55 kg C mol Leu −1 would have resulted in a serious overestimation (73%) of annual bacterial production rates. Our results emphasize the need for considering the temporal scale in CFs for bacterial production studies.

Kristin D. Bilyeu, Peiyu Zeng, Patricia Coello et al.

Plant Physiology • 2008

Abstract Phytic acid (PA) contains the major portion of the phosphorus in the soybean (Glycine max) seed and chelates divalent cations. During germination, both minerals and phosphate are released upon phytase-catalyzed degradation of PA. We generated a soybean line (CAPPA) in which an Escherichia coli periplasmic phytase, the product of the appA gene, was expressed in the cytoplasm of developing cotyledons. CAPPA exhibited high levels of phytase expression, ≥90% reduction in seed PA, and concomitant increases in total free phosphate. These traits were stable, and, although resulted in a trend for reduced emergence and a statistically significant reduction in germination rates, had no effect on the number of seeds per plant or seed weight. Because phytate is not digested by monogastric animals, untreated soymeal does not provide monogastrics with sufficient phosphorus and minerals, and PA in the waste stream leads to phosphorus runoff. The expression of a cytoplasmic phytase in the CAPPA line therefore improves phosphorus availability and surpasses gains achieved by other reported transgenic and mutational strategies by combining in seeds both high phytase expression and significant increases in available phosphorus. Thus, in addition to its value as a high-phosphate meal source, soymeal from CAPPA could be used to convert PA of admixed meals, such as cornmeal, directly to utilizable inorganic phosphorus.

Michael F. Coveney, Robert G. Wetzel

Applied and Environmental Microbiology • 1988

The relationship between bacterial growth and incorporation of [ methyl - 3 H]thymidine in oligotrophic lake water cultures was investigated. Prescreening, dilution, and addition of organic and inorganic nutrients were treatments used to prevent bacterivory and stimulate bacterial growth. Growth in unmanipulated samples was estimated through separate measurements of grazing losses. Both bacterial number and biovolume growth responses were measured, and incorporation of [ 3 H]thymidine in both total macromolecules and nucleic acids was assayed. The treatments had significant effects on conversion factors used to relate thymidine incorporation to bacterial growth. Cell number-based factors ranged from 1.1 × 10 18 to 38 × 10 18 cells mol of total thymidine incorporation −1 and varied with treatment up to 10-fold for the same initial bacterial assemblage. In contrast, cell biovolume-based conversion factors were similar for two treatment groups across a 16-fold range of [ 3 H]thymidine incorporation rates: 5.54 × 10 17 μm 3 mol of total thymidine incorporation −1 and 15.2 × 10 17 μm 3 mol of nucleic acid incorporation −1 . Much of the variation in cell number-based conversion factors was related to changes in apparent mean cell volume of produced bacteria. Phosphorus addition stimulated [ 3 H]thymidine incorporation more than it increased bacterial growth, which resulted in low conversion factors.

Laura Alonso‐Sáez, Jarone Pinhassi, Jakob Pernthaler et al.

Environmental Microbiology • 2010

Summary The suitability of applying empirical conversion factors (eCFs) to determine bacterial biomass production remains unclear because seawater cultures are usually overtaken by phylotypes that are not abundant in situ . While eCFs vary across environments, it has not been tested whether differences in eCFs are driven by changes in bacterial community composition or by in situ environmental conditions. We carried out seawater cultures throughout a year to analyse the correlation between eCFs and bacterial community structure, analysed by catalysed reporter deposition fluorescence in situ hybridization. Gammaproteobacteria usually dominated seawater cultures, but their abundance exhibited a wide range (25–73% of cell counts) and significantly increased with inorganic nutrient enrichment. Flavobacteria were less abundant but increased up to 40% of cells counts in winter seawater cultures, when in situ chlorophyll a was high. The correlations between eCFs and the abundance of the main broad phylogenetic groups ( Gamma‐, Alphaproteobacteria and Flavobacteria ) were significant, albeit weak, while more specific groups ( Alteromonadaceae and Rhodobacteraceae ) were not significantly correlated. Our results show that the frequent development of the fast‐growing group Alteromonadaceae in seawater cultures does not strongly drive the observed variations in eCFs. Rather, the results imply that environmental conditions and the growth of specific phylotypes interact to determine eCFs.

R. K. Clayton

Photochemistry and Photobiology • 1962

Summary Reversible light‐induced alteration of a special component of bacteriochlorophyll (BChl,) is observed in bacterial chromatophores. The alteration involves bleaching of the long‐wave absorption band at 870–890 mp and a blue shift of the band at 800 mp. Assuming that the altered BChl, molecule loses all of its long‐wave absorption, and that the extinction coefficient of this band is equal to that of the corresponding band in the major component of BChl, a quantum requirement could be computed for the light‐induced change. It was found with most preparations that two to four quanta suffice for the alteration of one BChl, molecule, even in dried chromatophores at 1° K. This result is taken as supporting evidence for the importance of light‐induced BChl, conversion in photosynthesis. It also shows that BChl, is effective as an energy sink in the chromatophore.

AJ Ramsay, RE Stannard, GJ Churchman

Soil Research • 1986

Water-stable aggregates and soil bacteria were studied from May to January in a field trial comparing soil structure under three treatments: wheat sown in ploughed soil, direct-drilled wheat and long-term grass. During the trial, both the proportion and size of macroaggregates (> 250 �m) tended to increase. These increases were accompanied by decreases in the proportions of particles in all smaller size ranges, including <2 �m, in the early part of the growing season, but, over summer, larger macroaggregates (> 2000 �m) increased at the expense of particles between 2000 and 63 �m. The highest proportion of larger macroaggregates occurred under grass, in all except the spring sampling, while the lowest proportion occurred in the ploughed soils. Numbers of bacteria, obtained by direct microscopy, were higher in the ploughed soil soon after ploughing than in the direct-drilled soil, but no other treatment effect was detected. In all plots, numbers of bacteria were lowest in November when the soil was the driest. There were up to twice as many bacteria per g of < 20 �m diameter fraction soil compared with the rest of the soil. Seasonal changes in the bacterial population of the <20 �m diameter fraction did not follow the changes in the whole soil.

kun li, xu han, ruiqiang ni et al.

Research Square • 2020

Abstract Background: Robinia pseudoacacia is a widely planted pioneer tree species in reforestations on barren mountains in northern China. Because of its nitrogen-fixing ability, it can play a positive role in soil and forest restoration. After clear-cutting of planted stands, R. pseudoacacia stands become coppice plantations. The impacts of shifting from seedling to coppice plantations on soil bacterial community and soil properties have not been well described. This study aims to quantify how soil properties and bacterial community composition vary between planted seedling versus coppice stands. Methods : Three 20×20 m plots were randomly selected in each seedling and coppice stand. The bulk soil and rhizosphere soil were sampled in the nine above-mentioned sample plots in the summer of 2017. Bulk soil was sampled at 10 cm from the soil surface using a soil auger. Rhizosphere soil samples were collected by brush. The soil samples were transported to the laboratory for chemical analysis and bacterial community composition and diversity was obtanied through DNA extraction, 16S rRNA gene amplification and high throughput sequencing. Results : The results showed that, compared to seedling plantations, soil quality decreased significantly in coppice stands, but without affecting soil exchangeable Mg 2+ and K + . Total carbon (C) and nitrogen (N) were lower in the rhizosphere than in bulk soil, whereas nutrient availability showed an opposite trend. The conversion from seedling to coppice plantations was also related to significant differences in soil bacterial community structure and to the reduction of soil bacterial α-diversity. Principal component analysis (PCA) showed that, bacterial community composition was similar in both bulk and rhizosphere soils in second generation coppice plantations. Specially, the conversion from seedling to coppice increased the relative abundance of Proteobacteria and Rhizobium , but reduced that of Actinobacteria , which may result in a decline of soil nutrient availability. Mantel tests revealed that C, N, Soil organic matter (SOM), nitrate nitrogen (NO 3 - -N) and available phosphorus positively correlated with bacterial community composition, while a variation partition analysis (VPA) showed that NO 3 - -N explained a relatively greater proportion of bacterial distribution (15.12%), compared with C and SOM. Surprinsingly, N showed no relationship with bacterial community composition, which may be related to nitrogen transportation. Conclusions : The conversion from seedling to coppice stands reduced soil quality and led to spatial-temporal homogenization of the soil bacterial community structure in both the rhizosphere and bulk soils. Such imbalance in microbial structure can accelerate the decline of R. pseudoacacia . This may affect the role of R. pseudoacacia coppice stands in soil and forest restoration of barren lands in mountain areas.

Melih Güzel

Biomass Conversion and Biorefinery • 2025

Abstract The short shelf life of bread can be attributed to changes in its textural and sensory properties, a process termed staling, and large amounts of bread residue and waste are generated daily. Because the main component of bread is starch, the use of bread wastes as a substrate for bacterial cellulose (BC) production can significantly contribute to valorisation and reuse of wastes. This study aimed to investigate the BC production potential of various stale breads, convert these wastes into usable forms for food and other industries, and increase their economic value. Stale breads were hydrolyzed with dilute acid, and BC-producing bacteria from Kombucha tea were isolated and identified as Gluconobacter oxydans MG2021 (GO). BCs were produced from bread hydrolysates with GO and Komagataeibacter hansenii GA2016 (KH), and their properties were examined. The results indicated that stale breads represented a good source for BC production, as high BC yields were obtained using GO (8.81%–25.02%) and all BCs had superior properties such as high crystallinity (75.96%–91.39%), thermal stability, liquid holding capacity, and fine fibers (40.16–85.39 nm). This study demonstrated that bread wastes could be used as a low-cost substrate for large-scale BC production, and the abundance of bread wastes demonstrated their potential as a resource for commercial BC producers.

Dalaq Aiysha, Zakia Latif

Journal of Basic Microbiology • 2022

Abstract Microbial enzymatic degradation of biowaste is a sustainable and environmentally friendly solution for eliminating biowaste pollution. It is the underlying cause of the ever‐increasing demand for harnessing multipurpose microbes to work as an entity under given complex processes. Twelve bacterial strains of bovine manure were evaluated for their hydrolytic enzyme activity and optimization. Six enzymes; cellulase, amylase, pectinase, chitinase, protease, and gelatinase were selected based on their corresponding abundant biowaste, that is, cellulose, proteinaceous, chitin, and polymeric starchy biowaste. The preliminary qualitative screening was followed by quantitative enzyme production as well as optimal enzyme production conditions. Irrespective of their sample source and origin, all strains showed the highest enzyme production when grown at 40°C for 72 h with pH 7. Comparatively, among the selected enzymes, strains were higher producers of cellulase, protease, and gelatinase. The present study reported the first time Brevibacillus parabrevis (DZ.15) as pectinase producer, Achromobacter spanius (DZ.1) as amylase‐protease‐chitinase producer, Achromobacter piechaudii (DZ.12) as pectinase‐chitinase‐gelatinase producer, and two Achromobacter kerstersii (DZ.16 and DZ.17) as pectinase‐chitinase producers. Therefore, this study suggested that bovine manure microbes exhibiting novel potential can be used for hydrolysis of environmental biowaste.

kun li, xu han, ruiqiang ni et al.

Research Square • 2020

Abstract Background: Robinia pseudoacacia is a widely planted pioneer tree species in reforestations on barren mountains in northern China. Because of its nitrogen-fixing ability, it can play a positive role in soil and forest restoration. After clear-cutting of planted stands, R. pseudoacacia stands become coppice plantations. The impacts of shifting from seedling to coppice stands on soil bacterial community and soil properties have not been well described. This study aims to quantify how soil properties and bacterial community composition vary between planted seedling versus coppice stands. Methods : Nine 20×20 m plots were randomly selected in seedling and coppice stands. The bulk soil and rhizosphere soil were sampled in summer 2017. Bulk soil was sampled at 10 cm from the soil surface using a soil auger. Rhizosphere soil samples were collected using a brush. The soil samples were transported to the laboratory for chemical analysis, and bacterial community composition and diversity was obtained through DNA extraction, 16S rRNA gene amplification and high-throughput sequencing. Results : The results showed that, compared to seedling plantations, soil quality decreased significantly in coppice stands, but without affecting soil exchangeable Mg 2+ and K + . Total carbon (C) and nitrogen (N) were lower in the rhizosphere than in bulk soil, whereas nutrient availability showed an opposite trend. The conversion from seedling to coppice plantations was also related to significant differences in soil bacterial community structure and to the reduction of soil bacterial α-diversity. Principal component analysis (PCA) showed that bacterial community composition was similar in both bulk and rhizosphere soils in second generation coppice plantations. Specially, the conversion from seedling to coppice stands increased the relative abundance of Proteobacteria and Rhizobium , but reduced that of Actinobacteria , which may result in a decline of soil nutrient availability. Mantel tests revealed that C, N, Soil organic matter (SOM), nitrate nitrogen (NO 3 - -N) and available phosphorus positively correlated with bacterial community composition, while a variation partition analysis (VPA) showed that NO 3 - -N explained a relatively greater proportion of bacterial distribution (15.12%), compared with C and SOM. Surprisingly, N showed no relationship with bacterial community composition, which may be related to nitrogen transportation. Conclusions : The conversion from seedling to coppice stands reduced soil quality and led to spatial-temporal homogenization of the soil bacterial community structure in both the rhizosphere and bulk soils. Such imbalance in microbial structure can accelerate the decline of R. pseudoacacia . This may affect the role of R. pseudoacacia coppice stands in soil and forest restoration of barren lands in mountain areas.

J E Vancauwenberge, P J Slininger, R J Bothast

Applied and Environmental Microbiology • 1990

beta-hydroxypropionaldehyde (3-HPA) can be oxidized to acrylic acid, an industrially important chemical used in the manufacture of synthetic plastics and other polymers. Of 19 genera and 55 strains tested, 3 Klebsiella and 2 Enterobacter strains produced 3-HPA. The most efficient strain was Klebsiella pneumoniae NRRL B-4011. Under optimum conditions (28 degrees C; 40 g of semicarbazide hydrochloride per liter, 70 g of glycerol per liter; and pH 6.0), 3.1 g of B-4011 cells per liter accumulated 22 g of 3-HPA per liter at a specific rate of 0.83 g/g per h; however, 14.5 g of cells per liter accumulated 46 g of 3-HPA per liter at a specific rate of 0.41 g/g per h.

Zhikang Wang, Chunlin Li, Zengchao Geng et al.

Research Square • 2023

Abstract Objective: The objective of this study is to address the research gap regarding the diversity and life strategies of organisms inhabiting soil environments formed by new restoration techniques such as aggregate spray-seeding (ASS), which currently remain unclear. Methods: We conducted a comparison between the ASS restoration area (SRA) and the natural vegetation area (NVA), as well as the ASS forest conversion area (FCA) and the traditional afforestation area (TAA) on Triangle Island, China. Environmental DNA sequencing was employed to analyze the diversity and life strategies of soil bacterial communities during both the summer and winter seasons. Results: The SRA and FCA showed significantly higher Chao1 index and relative abundance of r-strategy bacteria compared to NVA and TAA, along with lower DNA guanine-cytosine (GC) content. The soil bacterial communities of NVA and TAA were similar to each other, as were those of SRA and FCA. Proteobacteria and Acidobacteriota were found to be the dominant phyla in our studied soils, accounting for 67.83-76.54% of the total relative abundance. Proteobacteria had a higher relative abundance in summer, while Acidobacteriota had a higher relative abundance in winter. GC content exhibited a negative correlation (p < 0.0001) with the relative abundance of r-strategy bacteria and a positive correlation (p < 0.01) with the relative abundance of K-strategy bacteria. Conclusions: Our study demonstrates the impact of ASS application on the diversity and life strategy of soil bacterial communities, while also confirming the correlation between bacterial GC content and life strategy. These findings provide a basis for regulating soil microbial communities in ecological restoration projects.

Kun Li, Xu Han, Ruiqiang Ni et al.

Research Square • 2020

Abstract Background: Robinia pseudoacacia is a widely planted pioneer tree species in reforestations on barren mountains in northern China. Because of its nitrogen-fixing ability, it can play a positive role in soil and forest restoration. After clear-cutting of planted stands, R. pseudoacacia stands become coppice plantations. The impacts of shifting from seedling to coppice plantations on soil bacterial community and soil properties have not been well described. This study aims to quantify how soil properties and bacterial community composition vary between planted seedling versus coppice stands. Methods: Three 20 × 20 m plots were randomly selected in each seedling and coppice stand. The bulk soil and rhizosphere soil were sampled in the nine above-mentioned sample plots in the summer of 2017. Bulk soil was sampled at 10 cm from the soil surface using a soil auger. Rhizosphere soil samples were collected by brush. The soil samples were transported to the laboratory for chemical analysis and bacterial community composition and diversity was obtanied through DNA extraction, 16S rRNA gene amplification and high throughput sequencing. Results: The results showed that, compared to seedling plantations, soil quality decreased significantly in coppice stands, but without affecting soil exchangeable Mg 2+ and K 2+ . Total carbon (C) and nitrogen (N) were lower in the rhizosphere than in bulk soil, whereas nutrient availability showed an opposite trend. The conversion from seedling to coppice plantations was also related to significant differences in soil bacterial community structure and to the reduction of soil bacterial α-diversity. Principal component analysis (PCA) showed that, bacterial community composition was similar in both bulk and rhizosphere soils in second generation coppice plantations. Specially, the conversion from seedling to coppice increased the relative abundance of Proteobacteria and Rhizobium , but reduced that of Actinobacteria , which may result in a decline of soil nutrient availability. Mantel tests revealed that C, N, Soil organic matter (SOM), nitrate nitrogen (NO 3 − -N) and available phosphorus positively correlated with bacterial community composition, while a variation partition analysis (VPA) showed that NO 3 − -N explained a relatively greater proportion of bacterial distribution (15.12%), compared with C and SOM. Surprinsingly, N showed no relationship with bacterial community composition, which may be related to nitrogen transportation. Conclusions: The conversion from seedling to coppice stands reduced soil quality and led to spatial-temporal homogenization of the soil bacterial community structure in both the rhizosphere and bulk soils. Such imbalance in microbial structure can accelerate the decline of R. pseudoacacia . This may affect the role of R. pseudoacacia coppice stands in soil and forest restoration of barren lands in mountain areas.

Bahaa A. Hemdan, Mehrez E. El-Naggar, Sh. E. Abd-Elgawad et al.

Biomass Conversion and Biorefinery • 2024

Abstract Recently, the development of skin barrier depend on wound healing, which is one of the most complicated biological processes. As an alternative to conventional antibiotics, nanoparticles (NPs) have become more utilized generally to attack bacteria. Due to their distinct characteristics, potential microbicidal action, and ability to speed up the wound healing process, zinc oxide nanoparticles (ZnO-NPs) have attracted much attention. Biological techniques can solve the restrictions of both physical and chemical approaches for nanoparticles synthesis. Because it does not require expensive chemicals, high temperatures, or a lot of time, biological synthesis is relatively easy, inexpensive, and environmentally benign. The secondary metabolic extract from Escherichia coli was used in this study to biologically synthesize three distinct quantities of ZnO-NPs, which were then assessed for their effectiveness in wound healing and bacterial infection prevention. The biofabricated ZnO-NPs were fully characterized in terms of particle shape, morphology, and stability against aggregation. Depending on the concentration of the utilized zinc salt, three different samples were fabricated biologically, nominated as ZnO-NPs-1, ZnO-NPs-2, and ZnO-NPs-3. The findings of Uv-vis absorption peaks were obtained at 352 nm, demonstrating the preparation of ZnO-NPs. The results demonstrated the formation of ZnO-NPs with an average particle size of 79.19, 79.83 and 91.57 nm for the three prepared samples (ZnO-NPs-1, ZnO-NPs-2, and ZnO-NPs-3), respectively. Additionally, these samples of ZnO-NPs exhibited zeta potential values around −34.3, −33.7, and −33.4 mV, respectively. Energy dispersive X-ray confirmed the successful formation of ZnO-NPs. It was also observed from the obtained results that, ZnO-NP-3 showed superior antimicrobial potential against selected skin infectious microbes. The effective killing dosage of ZnO-NPs-3 was recorded to be 40 mg/L which can eliminate microbial growth. The dysregulation of skin flora significantly influences the etiology of inflammatory skin disorders.

Asmita Gaikwad, Kavita Jadhav, Shubhada Nayak

Current Agriculture Research Journal • 2023

Lignocellulosic biomass abundantly and ubiquitously occupies the earth. However, their complex molecular structure prevents their use as a source of organic material for fermentable sugars and nutrients to be used as foods, fertilizers and biofuels. For an efficient carbon cycle, microbial enzymes play a key role in slow biodegradation of lignocellulosic wastes in nature. Microbiological applications can enhance the rate of biodegradation to utilize agro-industrial and organic municipal solid wastes, containing up to 50% lignocellulose substrates, as an inexpensive and sustainable source of plant nutrients. With this hypothesis, the current study was carried out to prepare a consortium of lignocellulose degrading bacteria and use it to convert lignocellulosic substrates in garden, sugarcane, rice, cotton and fruit waste into biofertilizer. Overall, 7-14% reduction in cellulose and 3-6% reduction in lignin content, along with decrease in pH was observed on treatment of above wastes with microbial consortium in 42 days. In spite of the low conversion rates observed in our study, better root, shoot as well as leaf development was observed in moong seedlings grown in soil amended with biofertilizer (3:1 ratio) as compared to controls. Another interesting observation was the biofertilizers with low pH prepared from sugarcane wastes (pH 3.1) and fruit wastes (pH 3.6) supported plant growth more efficiently as compared to other biofertilizers (pH 5.0 to 5.7). Thus, in addition to feasible conversion of lignocellulosic wastes into biofertilizer, our study further suggests the use of selective wastes as raw material depending on the preference of plants for slightly acidic to neutral soil pH for growth.

C W Birky, J B Walsh

Genetics • 1992

Abstract We investigate the possibility that differences between synonymous substitution rates of organelle and bacterial genes differing only in copy number may be due to conversion bias. We find that the rather large observed difference in the synonymous rates between genes in the single copy and inverted-repeat regions of chloroplasts can be accounted for by a very small bias against new mutants. More generally, differences in the within-organelle fixation probability result in different apparent mutation rates as measured by the expected rate of appearance of cells homoplasmic for new mutants. Thus, differences in intracellular population parameters rather than molecular mechanisms can account for some variation in the apparent mutation rates of organelle genes, and possibly in other systems with variable numbers of gene copies. On the other hand, our analysis suggests that conversion bias is not a likely explanation for relatively low mutation rates observed near the replication origin of bacterial chromosomes.

W Wegst, U Tittmann, J Eberspächer et al.

Biochemical Journal • 1981

Strain E of chloridazon-degrading bacteria, when grown on L-phenylalanine accumulates cis-2,3-dihydro-2,3-dihydroxyphenylalanine. In experiments with resting cells and during growth the bacterium converts the aromatic carboxylic acids phenylacetate, phenylpropionate, phenylbutyrate and phenyl-lactate into the corresponding cis-2,3-dihydrodiol compounds. The amino acids L-phenylalanine, N-acetyl-L-phenylalanine and t-butyloxycarbonyl-L-phenylalanine were also transformed into dihydrodiols. All seven dihydrodiols, thus obtained, were characterized both by conventional analytical techniques and by the ability to serve as substrates for a cis-dihydrodiol dehydrogenase.

Sohta A. Ishikawa, Ryoma Kamikawa, Yuji Inagaki

Scientific Reports • 2015

Abstract Bacteria require two class-I release factors, RF1 and RF2, that recognize stop codons and promote peptide release from the ribosome. RF1 and RF2 were most likely established through gene duplication followed by altering their stop codon specificities in the common ancestor of extant bacteria. This scenario expects that the two RF gene families have taken independent evolutionary trajectories after the ancestral gene duplication event. However, we here report two independent cases of conversion between RF1 and RF2 genes ( RF1 - RF2 gene conversion), which were severely examined by procedures incorporating the maximum-likelihood phylogenetic method. In both cases, RF1 - RF2 gene conversion was predicted to occur in the region encoding nearly entire domain 3, of which functions are common between RF paralogues. Nevertheless, the ‘direction’ of gene conversion appeared to be opposite from one another—from RF2 gene to RF1 gene in one case, while from RF1 gene to RF2 gene in the other. The two cases of RF1-RF2 gene conversion prompt us to propose two novel aspects in the evolution of bacterial class-I release factors: (i) domain 3 is interchangeable between RF paralogues and (ii) RF1-RF2 gene conversion have occurred frequently in bacterial genome evolution.