Halophilic anaerobic fermentative bacteria

In hypersaline environments bacteria are exposed to a high osmotic pressure caused by the surrounding high salt concentrations. Halophilic microorganisms have specific strategies for balancing the osmotic pressure and surviving in these extreme conditions. Halophilic fermentative bacteria form taxonomically and phylogenetically a coherent group mainly belonging to the order Halanaerobiales. In this review, halophilic anaerobic fermentative bacteria in terms of taxonomy and phylogeny, special characteristics, survival strategies, and potential for biotechnological applications in a wide variety of branches, such as production of hydrogen, are discussed.     

The genomes of fermentative Saccharomyces

Many different yeast species can take part in spontaneous fermentations, but the species of the genus Saccharomyces, including Saccharomyces cerevisiae in particular, play a leading role in the production of fermented beverages and food. In recent years, the development of whole-genome scanning techniques, such as DNA chip-based analysis and high-throughput sequencing methods, has considerably increased our knowledge of fermentative Saccharomyces genomes, shedding new light on the evolutionary history of domesticated strains and the molecular mechanisms involved in their adaptation to fermentative niches. Genetic exchange frequently occurs between fermentative Saccharomyces and is an important mechanism for generating diversity and for adaptation to specific ecological niches. We review and discuss here recent advances in the genomics of Saccharomyces species and related hybrids involved in major fermentation processes.     

Studies on fermentative production of squalene

Fermentative production of squalene under anaerobic conditions using commercially available compressed baker's yeast (Saccharomyces cerevisiae), and a strain of Torulaspora delbrueckii isolated from molasses was studied. Yield of squalene from S. cerevisiae and T. delbrueckii were found to be 41.16 and 237.25 g g^–1 respectively, dry weight of yeast cells. Isolation and purification of squalene from the lipid extracts obtained by cell lysis of either strain were achieved chromatographically. The purified squalene was characterized spectroscopically against an authentic standard.     

Modeling and optimization of fermentative hydrogen production

Biohydrogen is a sustainable energy resource due to its potentially higher efficiency of conversion to usable power, non-polluting nature and high energy density. The purpose of modeling and optimization is to improve, analyze and predict biohydrogen production. Biohydrogen production depends on a number of variables, including pH, temperature, substrate concentration and nutrient availability, among others. Mathematical modeling of several distinct processes such as kinetics of microbial growth and products formation, steady state behavior of organic substrate along with its utilization and inhibition have been presented. Present paper summarizes the experimental design methods used to investigate effects of various factors on fermentative hydrogen production, including one-factor-at-a-time design, full factorial and fractional factorial designs. Each design method is briefly outlined, followed by the introduction of its analysis. In addition, the applications of artificial neural network, genetic algorithm, principal component analysis and optimization process using desirability function have also been highlighted.     

The fermentative characteristics of anaerobic rumen fungi

Substrate utilization and fermentation characteristics of rumen fungi of the genus Neocallimastix are described. Preliminary observations on the removal of monosaccharides from plant cell walls and the effect of fermentation products on growth of Neocallimastix sp. (isolate R1) are presented. The properties of rumen fungi are discussed in relation to their role in the rumen.     

Physiology of dark fermentative growth of Rhodopseudomonas capsulata

The photosynthetic bacterium Rhodopseudomonas capsulata can grow under anaerobic conditions with light as the energy source or, alternatively, in darkness with D-fructose or certain other sugars as the sole source of carbon and energy. Growth in the latter mode requires an "accessory oxidant" such as trimethylamine-N-oxide, and the resulting cells contain the photosynthetic pigments characteristic of R. capsulata (associated with intracytoplasmic membranes) and substantial deposits of poly-beta-hydroxybutyrate. In dark anaerobic batch cultures in fructose plus trimethylamine-N-oxide medium, trimethylamine formation parallels growth, and typical fermentation products accumulate, namely, CO2 and formic, acetic, and lactic acids. These products are also found in dark anaerobic continuous cultures of R. capsulata; acetic acid and CO2 predominate when fructose is limiting, whereas formic and lactic acids are observed at elevated concentrations when trimethylamine-N-oxide is the limiting nutrient. Evidence is presented to support the conclusions that ATP generation during anaerobic dark growth of R. capsulata on fructose plus trimethylamine-N-oxide occurs by substrate level phosphorylations associated with classical glycolysis and pyruvate dissimilation, and that the required accessory oxidant functions as an electron sink to permit the management of fermentative redox balance, rather than as a terminal electron acceptor necessary for electron transport-driven phosphorylation.     

弧菌菌株发酵工艺初步研究

采用摇瓶培养和发酵罐培养并在不同培养时间测定菌液浊度和活菌数,为弧菌灭活疫苗生产工艺提供参数.研究结果表明,摇瓶培养装量以30%较为合适,培养基初始pH 7.5,发酵过程以不再控制为宜.初步确定了弧菌发酵培养工艺参数:弧菌菌株接种TSB,28 ℃摇瓶培养18～20 h,28 ℃种子罐通气搅拌培养12～14 h,28 ℃...     

Improvement of fermentative hydrogen production: various approaches

Fermentation of biomass or carbohydrate-based substrates presents a promising route of biological hydrogen production compared with photosynthetic or chemical routes. Pure substrates, including glucose, starch and cellulose, as well as different organic waste materials can be used for hydrogen fermentation. Among a large number of microbial species, strict anaerobes and facultative anaerobic chemoheterotrophs, such as clostridia and enteric bacteria, are efficient producers of hydrogen. Despite having a higher evolution rate of hydrogen, the yield of hydrogen [mol H₂ (mol substrate^–1)] from fermentative processes is lower than that achieved using other methods; thus, the process is not economically viable in its present form. The pathways and experimental evidence cited in the literature reveal that a maximum of four mol of hydrogen can be obtained from substrates such as glucose. Modifications of the fermentation process, by redirection of metabolic pathways, gas sparging and maintaining a low partial pressure of hydrogen to make the reaction thermodynamically favorable, efficient product removal, optimum bioreactor design and integrating fermentative process with that of photosynthesis, are some of the ways that have been attempted to improve hydrogen productivity. This review briefly describes recent advances in these approaches towards improvement of hydrogen yield by fermentation.     

Evaluation of metabolism using stoichiometry in fermentative biohydrogen

We first constructed full stoichiometry, including cell synthesis, for glucose mixed-acid fermentation at different initial substrate concentrations (0.8-6 g-glucose/L) and pH conditions (final pH 4.0-8.6), based on experimentally determined electron-equivalent balances. The fermentative bioH2 reactions had good electron closure (-9.8 to +12.7% for variations in glucose concentration and -3 to +2% for variations in pH), and C, H, and O errors were below 1%. From the stoichiometry, we computed the ATP yield based on known fermentation pathways. Glucose-variation tests (final pH 4.2-5.1) gave a consistent fermentation pattern of acetate + butyrate + large H2, while pH significantly shifted the catabolic pattern: acetate + butyrate + large H2 at final pH 4.0, acetate + ethanol + modest H2 at final pH 6.8, and acetate + lactate + trivial H2 at final pH 8.6. When lactate or propionate was a dominant soluble end product, the H2 yield was very low, which is in agreement with the theory that reduced ferredoxin (Fd(red)) formation is required for proton reduction to H2. Also consistent with this hypothesis is that high H2 production correlated with a high ratio of butyrate to acetate. Biomass was not a dominant sink for electron equivalents in H2 formation, but became significant (12%) for the lowest glucose concentration (i.e., the most oligotrophic condition). The fermenting bacteria conserved energy similarly at approximately 3 mol ATP/mol glucose (except 0.8 g-glucose/L, which had approximately 3.5 mol ATP/mol glucose) over a wide range of H2 production. The observed biomass yield did not correlate with ATP conservation; low observed biomass yields probably were caused by accelerated rates of decay or production of soluble microbial products.     

Developing fermentative terpenoid production for commercial usage

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Improving the yield from fermentative hydrogen production

Efforts to increase H₂ yields from fermentative H₂ production include heat treatment of the inoculum, dissolved gas removal, and varying the organic loading rate. Although heat treatment kills methanogens and selects for spore-forming bacteria, the available evidence indicates H₂ yields are not maximized compared to bromoethanesulfonate, iodopropane, or perchloric acid pre-treatments and spore-forming acetogens are not killed. Operational controls (low pH, short solids retention time) can replace heat treatment. Gas sparging increases H₂ yields compared to un-sparged reactors, but no relationship exists between the sparging rate and H₂ yield. Lower sparging rates may improve the H₂ yield with less energy input and product dilution. The reasons why sparging improves H₂ yields are unknown, but recent measurements of dissolved H₂ concentrations during sparging suggest the assumption of decreased inhibition of the H₂-producing enzymes is unlikely. Significant disagreement exists over the effect of organic loading rate (OLR); some studies show relatively higher OLRs improve H₂ yield while others show the opposite. Discovering the reasons for higher H₂ yields during dissolved gas removal and changes in OLR will help improve H₂ yields.     

Sulfonate-sulfur can be assimilated for fermentative growth

Abstract Bacterial assimilation of sulfonate-sulfur under anaerobic conditions has been demonstrated. Two different bacteria able to grow fermentatively using sulfonate-sulfur as sole sulfur source were isolated by enrichment culture; neither were able to utilize sulfonates as sole source of carbon and energy for growth. The isolate of Clostridium pasteurianum assimilated the sulfur of isethionate (2-hydroxyethanesulfonate), taurine (2-aminoethanesulfonate), or p -toluenesulfonate. A facultatively fermentative Klebsiella strain did not utilize the sulfur of any of these sulfonates, but assimilated cysteate-sulfur; in contrast, when growing by aerobic respiration, the range of sulfonates able to serve as sulfur source was greater. Both bacteria displayed a preferential utilization of sulfate-sulfur to that of the sulfonates tested. Thus, bacterial assimilation of sulfonate-sulfur during anaerobic growth has direct parallels with features until now recognized only for aerobic assimilatory processes.     

Towards large scale fermentative production of succinic acid

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Lactobacillus kefiranofaciens流加发酵法生产开菲尔多糖

研究了开菲尔基质乳杆菌(Lactobacillus kefiranofaciens)在不同初始蔗糖浓度下的开菲尔多糖(Kefiran)分批发酵过程.结果表明,分批发酵过程不能实现Kefiran高产量、高底物转化率和高生产强度的相对统一.在此基础上,进一步考察分批补料、恒速流加和指数速率流加等不同培养方式对Kefiran发酵的影响.这几种培养方式都可以实现乳酸菌细胞和Kefiran的高产.综合比较,4g/(L·h)的蔗糖恒速流加为Kefiran生产较适宜的流加方式,细胞干质量浓度为63.6 g/L,Kefiran产量达到4.95 g/L.     

Metabolic energy conservation for fermentative product formation

Microbial production of bulk chemicals and biofuels from carbohydrates competes with low-cost fossil-based production. To limit production costs, high titres, productivities and especially high yields are required. This necessitates metabolic networks involved in product formation to be redox-neutral and conserve metabolic energy to sustain growth and maintenance. Here, we review the mechanisms available to conserve energy and to prevent unnecessary energy expenditure. First, an overview of ATP production in existing sugar-based fermentation processes is presented. Substrate-level phosphorylation (SLP) and the involved kinase reactions are described. Based on the thermodynamics of these reactions, we explore whether other kinase-catalysed reactions can be applied for SLP. Generation of ion-motive force is another means to conserve metabolic energy. We provide examples how its generation is supported by carbon-carbon double bond reduction, decarboxylation and electron transfer between redox cofactors. In a wider perspective, the relationship between redox potential and energy conservation is discussed. We describe how the energy input required for coenzyme A (CoA) and CO₂ binding can be reduced by applying CoA-transferases and transcarboxylases. The transport of sugars and fermentation products may require metabolic energy input, but alternative transport systems can be used to minimize this. Finally, we show that energy contained in glycosidic bonds and the phosphate-phosphate bond of pyrophosphate can be conserved. This review can be used as a reference to design energetically efficient microbial cell factories and enhance product yield.     

Occurrence and properties of lactic dehydrogenases of fermentative mycoplasmas

Eight fermentative mycoplasmas differing in genome size, deoxyribonucleic acid (DNA) base composition, or sterol dependence were examined for lactic dehydrogenase composition by spectrophotometric assay and polyacrylamide gel electrophoresis. Three completely different patterns of lactic dehydrogenase composition were found. (i) A nicotinamide adenine dinucleotide (NAD)-dependent l(+)-lactic dehydrogenase was found in Mycoplasma pneumoniae, M. gallisepticum, M. mycoides var. mycoides, mycoplasma UM 30847, M. neurolyticum, and Acholeplasma axanthum. Electrophoresis of cell-free extracts of each of these mycoplasmas produced, with the exception of M. mycoides var. mycoides and UM 30847, single, different enzyme bands. M. mycoides var. mycoides and UM 30847 were similar and formed multiple bands of enzyme activity. We were unable to establish whether these multiple bands were due to lactic dehydrogenase isoenzymes or artifacts. (ii) An NAD-dependent d(-)-lactic dehydrogenase which could not be reversed to oxidize lactate was found in M. fermentans. (iii) A. laidlawii A possessed an NAD-independent d(-)-lactic dehydrogenase capable of reducing dichlorophenol-indophenol, and an NAD-dependent l(+)-lactic dehydrogenase which is specifically activated by fructose-1,6-diphosphate. Heretofore, this enzyme regulatory mechanism was known to occur only among the Lactobacillaceae. No yeast-type lactic dehydrogenase activity was found in any of the mycoplasmas examined. The stereoisomer of lactic acid accumulated during growth correlated perfectly with the type of NAD-dependent lactic dehydrogenase found in each mycoplasma. The types of lactic dehydrogenase activity found in these mycoplasmas were not related to genome size, DNA base composition, or sterol dependence.     

Studies on fermentative production of rifamycin using Amycolatopsis mediterranei

The fermentative production of rifamycin by Amycolatopsis mediterranei (MTCC17) has been studied. Both qualitative and quantitative aspects of the fermentation were determined by optimizing cultural conditions and medium design to improve the production of rifamycin. A pH value of 7.0, a temperature of 26°C, an aeration rate of 250rev/min for a 50ml volume, a level of inoculum of 10% grown aeration for 48h and a fermentation period of 11days were found to be optimum. Among the nitrogen sources, and culture conditions, peanut meal and aeration were found to be critical for rifamycin production respectively. The above mentioned exercise increased the yields of rifamycin from 350mg/l to 2000mg/l.     

Enhancement effect of hematite nanoparticles on fermentative hydrogen production

The effects of hematite nanoparticles concentration (0-1600 mg/L) and initial pH (4.0-10.0) on hydrogen production were investigated in batch assays using sucrose-fed anaerobic mixed bacteria at 35 °C. The optimum hematite nanoparticles concentration with an initial pH 8.48 was 200 mg/L, with the maximum hydrogen yield of 3.21 mol H₂/mol sucrose which was 32.64% higher than the blank test. At 200 mg/L hematite nanoparticles concentration, further initial pH optimization experiments indicated that at pH 6.0 the maximum hydrogen yield reached to 3.57 mol H₂/mol sucrose and hydrogen content was 66.1%. The slow release of hematite nanoparticles had been recorded by transmission electron microscopy (TEM). In addition, TEM analysis indicated that the hematite nanoparticles can affect the shape of bacteria, namely, its length increased from ca. 2.0-3.6 μm to ca. 2.6-5.6 μm, and width became narrower.