Relative Importance of Trophic Group Concentrations during Anaerobic Degradation of Volatile Fatty Acids

Although obligate syntrophic reactions cannot proceed without hydrogenotrophs, it has been unclear from the literature whether potential improvements are achievable with higher concentrations of hydrogenotrophs. In this study, the relative importance of formate-/H₂-utilizing and acetate-utilizing trophic groups in the anaerobic degradation of butyrate and propionate was assessed by adding various proportions of these enriched cultures to a mixed anaerobic seed inoculum. The improvement resulting from the additional acetate-utilizing cultures was much greater than with formate/H₂ utilizers. Furthermore, formate/H₂ utilizers did not improve propionate utilization significantly, suggesting the importance of optimum utilization of hydrogenotrophic capacity. During most of the volatile fatty acid (VFA) degradation period, the system responded with characteristic hydrogen levels to maintain the Gibbs free energy of oxidation approximately constant for both butyrate (−6 kJ) and propionate (−14 kJ). These free-energy values were independent of methanogenic activity, as well as the volume of the seed inoculum and the VFA concentrations present. By comparing the experimental results with kinetic and mass transfer models, it was postulated that the diffusional transfer of reducing equivalents was the major limiting factor for efficient VFA degradation. Therefore, for optimum utilization of the hydrogenotrophs, low acetate concentrations are vital to enable the system to respond with higher formate/H₂ levels, thus leading to improved transfer of reducing equivalents. Due to the small number of propionate utilizers (and hence their limited surface area) and low bulk liquid concentrations, the additional formate/H₂ utilizers were of minimal use for improving the degradation rate further. The butyrate degradation rates strongly correlated with the cumulative activity of hydrogenotrophs and acetotrophs over the experimental range studied, indicating the need to model obligate syntrophic reactions as a dependent function of methanogenic activity.     

Response surface methodology analysis of anaerobic syntrophic degradation of volatile fatty acids in an upflow anaerobic sludge bed reactor inoculated with enriched cultures

Anaerobic oxidation of volatile fatty acids (VFAs) as the key intermediates is restricted thermodynamically. Presently, enriched acetogenic and methanogenic cultures were used for syntrophic anaerobic digestion of VFAs in an upflow anaerobic sludge bed reactor fed with acetic, propionic, and butyric acids at maximum concentrations of 5.0, 3.0, and 4.0 g/L, respectively. Interactive effects of propionate, butyrate and acetate were analyzed. Hydraulic retention time (HRT) and acetate oxidizing syntrophs and methanogen (hydrogenotrophs) to syntrophic bacteria (propionate- and butyrate-oxidizing bacteria) population ratio (M/A) were investigated as key microbiological and operating variables of VFA anaerobic degradations. M/A did not affect the size distribution and had little effect on extracellular polymer contents of the granules. Granular sludge with close spatial microbial proximity enhanced syntrophic degradation of VFAs compared to other cultures, such as suspended cultures. Optimum conditions were found to be propionate = 1.93 g/L, butyrate = 2.15 g/L, acetate = 2.50 g/L, HRT = 22 h, and M/A = 2.5 corresponding to maximum VFA removal and biogas production rate. Results of verification experiments and predicted values from fitted correlations were in close agreement at the 95% confidence interval. Granules seemed to be smaller particles and less stable in construction with an irregular fractured surface compared to the original granules.     

Sulfate reduction in methanogenic bioreactors

Abstract: In the anaerobic treatment of sulfate-containing wastewater, sulfate reduction interferes with methanogenesis. Both mutualistic and competitive interactions between sulfate-reducing bacteria and methanogenic bacteria have been observed. Sulfate reducers will compete with methanogens for the common substrates hydrogen, formate and acetate. In general, sulfate reducers have better growth kinetic properties than methanogens, but additional factors which may be of importance in the competition are adherence properties, mixed substrate utilization, affinity for sulfate of sulfate reducers, relative numbers of bacteria, and reactor conditions such as pH, temperature and sulfide concentration. Sulfate reducers also compete with syntrophic methanogenic consortia involved in the degradation of substrates like propionate and butyrate. In the absence of sulfate these methanogenic consortia are very important, but in the presence of sulfate they are thought to be easily outcompeted by sulfate reducers. However, at relatively low sulfate concentrations, syntrophic degradation of propionate and butyrate coupled to HZ removal via sulfate reduction rather than via methanogenesis may become important. A remarkable feature of some sulfate reducers is their ability to grow fermentatively or to grow in syntrophic association with methanogens in the absence of sulfate.     

Energetics of syntrophic fatty acid oxidation

Abstract: Fatty acids are key intermediates in methanogenic degradation of organic matter in sediments as well as in anaerobic reactors. Conversion of butyrate or propionate to acetate, (CO₂), and hydrogen is endergonic under standard conditions, and becomes possible only at low hydrogen concentrations (10^-4-10^-5 bar). A model of energy sharing between fermenting and methanogenic bacteria attributes a maximum amount of about 20 kJ per mol reaction to each partner in this syntrophic cooperation system. This amount corresponds to synthesis of only a fraction (one-third) of an ATP to be synthesized per reaction. Recent studies on the biochemistry of syntrophic fatty acid-oxidizing bacteria have revealed that hydrogen release from butyrate by these bacteria is inhibited by a protonophore or the ATPase inhibitor DCCD ( N , N '-dicyclohexyl carbodiimide), indicating that a reversed electron transport step is involved in butyrate or propionate oxidation. Hydrogenase, butyryl-CoA dehydrogenase, and succinate dehydrogenase acitivities were found to be partially associated with the cytoplasmic membrane fraction. Also glycolic acid is degraded to methane and CO₂ by a defined syntrophic coculture. Here the most difficult step for hydrogen release is the glycolate dehydrogenase reaction ( E '₀=−92 mV). Glycolate dehydrogenase, hydrogenase, and ATPase were found to be membrane-bound enzymes. Membrane vesicles produced hydrogen from glycolate only in the presence of ATP; protonophores and DCCD inhibited this hydrogen release. This system provides a suitable model to study reversed electron transport in interspecies hydrogen transfer between fermenting and methanogenic bacteria in methanogenic biomass degradation.     

Perturbation of syntrophic isobutyrate and butyrate degradation with formate and hydrogen

The effect of formate and hydrogen on isomerization and syntrophic degradation of butyrate and isobutyrate was investigated using a defined methanogenic culture, consisting of syntrophic isobutyrate-butyrate degrader strain IB, Methanobacterium formicicum strain T1N, and Methanosarcina mazeii strain T18. Formate and hydrogen were used to perturb syntrophic butyrate and isobutyrate degradation by the culture. The reversible isomerization between isobutyrate and butyrate was inhibited by the addition of either formate or hydrogen, indicating that the isomerization was coupled with syntrophic butyrate degradation for the culture studied. Energetic analysis indicates that the direction of isomerization between isobutyrate and butyrate is controlled by the ratio between the two acids, and the most thermodynamically favorable condition for the degradation of butyrate or isobutyrate in conjunction with the isomerization is at almost equal concentrations of isobutyrate and butyrate. The degradation of isobutyrate and butyrate was completely inhibited in the presence of a high hydrogen partial pressure (>2000 Pa) or a measurable level of formate (10 muM or higher). Significant formate (more than 1 mM) was detected during the perturbation with hydrogen (17 to 40 kPa). Resumption of butyrate and isobutyrate degradation was related to the removal of formate. Energetic analysis supported that formate was another electron carrier, besides hydrogen, during syntrophic isobutyrate-butyrate degradation by this culture. (c) 1996 John Wiley & Sons, Inc.     

Thermophilic anaerobic degradation of butyrate by a butyrate-utilizing bacterium in coculture and triculture with methanogenic bacteria

We studied syntrophic butyrate degradation in thermophilic mixed cultures containing a butyrate-degrading bacterium isolated in coculture with Methanobacterium thermoautotrophicum or in triculture with M. thermoautotrophicum and the TAM organism, a thermophilic acetate-utilizing methanogenic bacterium. Butyrate was beta-oxidized to acetate with protons as the electron acceptors. Acetate was used concurrently with its production in the triculture. We found a higher butyrate degradation rate in the triculture, in which both hydrogen and acetate were utilized, than in the coculture, in which acetate accumulated. Yeast extract, rumen fluid, and clarified digestor fluid stimulated butyrate degradation, while the effect of Trypticase was less pronounced. Penicillin G, d-cycloserine, and vancomycin caused complete inhibition of butyrate utilization by the cultures. No growth or degradation of butyrate occurred when 2-bromoethanesulfonic acid or chloroform, specific inhibitors of methanogenic bacteria, was added to the cultures and common electron acceptors such as sulfate, nitrate, and fumarate were not used with butyrate as the electron donor. Addition of hydrogen or oxygen to the gas phase immediately stopped growth and butyrate degradation by the cultures. Butyrate was, however, metabolized at approximately the same rate when hydrogen was removed from the cultures and was metabolized at a reduced rate in the cultures previously exposed to hydrogen.     

Evidence for H2 and formate formation during syntrophic butyrate and propionate degradation

Both H2 and formate were formed during butyrate oxidation by Syntrophospora bryantii with pentenoate as electron acceptor and during propionate oxidation by a mesophilic propionate oxidizing bacterium (MPOB) with fumarate as electron acceptor. H2 and formate levels were affected by the bicarbonate concentration. S bryantii and MPOB were also able to interconvert formate and H2+ HCO3-; the apparent K(M) values for formate were of 2.9 mM and 1.8 mM, respectively. The conversion of H2+ HCO3- to formate was detected only when the H2 partial pressure was above 80 kPa. This interconversion seems to be rather unimportant under conditions prevailing during syntrophic propionate and butyrate oxidation.     

典型煤层水微生物产甲烷潜力及其群落结构研究

内蒙古自治区二连盆地、海拉尔盆地是我国重要的煤层气产区,其中生物成因煤层气是煤层气的重要来源,但复杂物质转化产甲烷相关微生物群落结构及功能尚不清楚。【目的】研究煤层水中的微生物代谢挥发性脂肪酸产甲烷的生理特征及群落特征。【方法】以内蒙古自治区二连盆地和海拉尔盆地的四口煤层气井水作为接种物,分别添加乙酸钠、丙酸钠和丁酸钠厌氧培养;定期监测挥发性脂肪酸降解过程中甲烷和底物的变化趋势,应用高通量测序技术,分析原始煤层气井水及稳定期产甲烷菌液的微生物群落结构。【结果】除海拉尔盆地H303煤层气井微生物不能代谢丙酸外,其他样品均具备代谢乙酸、丙酸和丁酸产生甲烷的能力,其生理生态参数存在显著差异,产甲烷延滞期依次是乙酸<丁酸<丙酸;最大比产甲烷速率和底物转化效率依次是丙酸<乙酸<丁酸。富集培养后,古菌群落结构与煤层气井水的来源显著相关,二连盆地优势古菌为氢营养型产甲烷古菌Methanocalculus (相对丰度13.5%–63.4%)和复合营养型产甲烷古菌Methanosarcina (7.9%–51.3%),海拉尔盆地的优势古菌为氢营养型产甲烷古菌Methanobact...     

Effects of acetate, propionate, and butyrate on the thermophilic anaerobic degradation of propionate by methanogenic sludge and defined cultures.

The effects of acetate, propionate, and butyrate on the anaerobic thermophilic conversion of propionate by methanogenic sludge and by enriched propionate-oxidizing bacteria in syntrophy with Methanobacterium thermoautotrophicum delta H were studied. The methanogenic sludge was cultivated in an upflow anaerobic sludge bed (UASB) reactor fed with propionate (35 mM) as the sole substrate for a period of 80 days. Propionate degradation was shown to be severely inhibited by the addition of 50 mM acetate to the influent of the UASB reactor. The inhibitory effect remained even when the acetate concentration in the effluent was below the level of detection. Recovery of propionate oxidation occurred only when acetate was omitted from the influent medium. Propionate degradation by the methanogenic sludge in the UASB reactor was not affected by the addition of an equimolar concentration (35 mM) of butyrate to the influent. However, butyrate had a strong inhibitory effect on the growth of the propionate-oxidizing enrichment culture. In that case, the conversion of propionate was almost completely inhibited at a butyrate concentration of 10 mM. However, addition of a butyrate-oxidizing enrichment culture abolished the inhibitory effect, and propionate oxidation was even stimulated. All experiments were conducted at pH 7.0 to 7.7. The thermophilic syntrophic culture showed a sensitivity to acetate and propionate similar to that of mesophilic cultures described in the literature. Additions of butyrate or acetate to the propionate medium had no effect on the hydrogen partial pressure in the biogas of an UASB reactor, nor was the hydrogen partial pressure in propionate-degrading cultures affected by the two acids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of hydrogen and formate on the degradation of propionate and butyrate in thermophilic granules from an upflow anaerobic sludge blanket reactor.

Degradation of propionate and butyrate in whole and disintegrated granules from a thermophilic (55 degrees C) upflow anaerobic sludge blanket reactor fed with acetate, propionate, and butyrate as substrates was examined. The propionate and butyrate degradation rates in whole granules were 1.16 and 4.0 mumol/min/g of volatile solids, respectively, and the rates decreased 35 and 25%, respectively, after disintegration of the granules. The effect of adding different hydrogen-oxidizing bacteria (both sulfate reducers and methanogens), some of which used formate in addition to hydrogen, to disintegrated granules was tested. Addition of either Methanobacterium thermoautotrophicum delta H, a hydrogen-utilizing methanogen that does not use formate, or Methanobacterium sp. strain CB12, a hydrogen- and formate-utilizing methanogen, to disintegrated granules increased the degradation rate of both propionate and butyrate. Furthermore, addition of a thermophilic sulfate-reducing bacterium (a Desulfotomaculum sp. isolated in our laboratory) to disintegrated granules improved the degradation of both substrates even more than the addition of methanogens. By monitoring the hydrogen partial pressure in the cultures, a correlation between the hydrogen partial pressure and the degradation rate of propionate and butyrate was observed, showing a decrease in the degradation rate with increased hydrogen partial pressure. No significant differences in the stimulation of the degradation rates were observed when the disintegrated granules were supplied with methanogens that utilized hydrogen only or hydrogen and formate. This indicated that interspecies formate transfer was not important for stimulation of propionate and butyrate degradation.     

Performance of anaerobic granules for degradation of pentachlorophenol.

Anaerobic granules degrading pentachlorophenol (PCP) with specific PCP removal activity up to 14.6 mg/g of volatile suspended solids per day were developed in a laboratory-scale anaerobic upflow sludge blanket reactor at 28 degrees C, by using a mixture of acetate, propionate, butyrate, and methanol as the carbon source. The reactor was able to treat synthetic wastewater containing 40 to 60 mg of PCP per liter at a volumetric loading rate of up to 90 mg/liter of reactor volume per day, with a hydraulic retention time of 10.8 to 15 h. PCP removal of more than 99% was achieved. Results of adsorption of PCP by granular biomass indicated that the PCP removal by the granules was due to biodegradation rather than adsorption. A radiotracer assay demonstrated that the PCP-degrading granules mineralized [14C]PCP to 14CH4 and 14CO2. Toxicity test results indicated that syntrophic propionate degraders and acetate-utilizing methanogens were more sensitive to PCP than syntrophic butyrate degraders. The PCP-degrading granules also exhibited a higher tolerance to the inhibition caused by PCP for methane production and degradation of acetate, propionate, and butyrate, compared with anaerobic granules unadapted to PCP.     

Contribution of 13C-NMR spectroscopy to the elucidation of pathways of propionate formation and degradation in methanogenic environments

Propionate is an important intermediate in the anaerobic degradation of complex organic matter to methane and carbon dioxide. The metabolism of propionate-forming and propionate-degrading bacteria is reviewed here. Propionate is formed during fermentation of polysaccharides, proteins and fats. The study of the fate of 13C-labelled compounds by nuclear magnetic resonance (NMR) spectroscopy has contributed together with other techniques to the present knowledge of the metabolic routes which lead to propionate formation from these substrates. Since propionate oxidation under methanogenic conditions is thermodynamically difficult, propionate often accumulates when the rates of its formation and degradation are unbalanced. Bacteria which are able to degrade propionate to the methanogenic substrates acetate and hydrogen can only perform this reaction when the methanogens consume acetate and hydrogen efficiently. As a consequence, propionate can only be degraded by obligatory syntrophic consortia of microorganisms. NMR techniques were used to study the degradation of propionate by defined and less defined cultures of these syntrophic consortia. Different types of side-reactions were reported, like the reductive carboxylation to butyrate and the reductive acetylation to higher fatty acids.     

Anaerobic Degradation of Normal- and Branched-Chain Fatty Acids with Four or More Carbons to Methane by a Syntrophic Methanogenic Triculture

Syntrophic degradation of normal- and branched-chain fatty acids with 4 to 9 carbons was investigated with a mesophilic syntrophic isobutyrate-butyrate-degrading triculture consisting of the non-spore-forming, syntrophic, fatty acid-degrading, gram-positive rod-shaped strain IB, Methanobacterium formicicum T1N, and Methanosarcina mazei T18. This triculture converted butyrate and isobutyrate to methane and converted valerate and 2-methylbutyrate to propionate and methane. This triculture also degraded caproate, 4-methylvalerate, heptanoate, 2-methylhexanoate, caprylate, and pelargoate. During the syntrophic conversion of isobutyrate and butyrate, a reversible isomerization between butyrate and isobutyrate occurred; isobutyrate and butyrate were isomerized to the other isomeric form to reach nearly equal concentrations and then their concentrations decreased at the same rates. Butyrate was an intermediate of syntrophic isobutyrate degradation. When butyrate was degraded in the presence of propionate, 2-methylbutyrate was synthesized from propionate and isobutyrate formed from butyrate. During the syntrophic degradation of valerate, isobutyrate, butyrate, and 2-methylbutyrate were formed and then degraded. During syntrophic degradation of 2-methylbutyrate, isobutyrate and butyrate were formed and then degraded.     

A Proteomic View at the Biochemistry of Syntrophic Butyrate Oxidation in Syntrophomonas wolfei

In syntrophic conversion of butyrate to methane and CO₂, butyrate is oxidized to acetate by secondary fermenting bacteria such as Syntrophomonas wolfei in close cooperation with methanogenic partner organisms, e.g., Methanospirillum hungatei. This process involves an energetically unfavourable shift of electrons from the level of butyryl-CoA oxidation to the substantially lower redox potential of proton and/or CO₂ reduction, in order to transfer these electrons to the methanogenic partner via hydrogen and/or formate.In the present study, all prominent membrane-bound and soluble proteins expressed in S. wolfei specifically during syntrophic growth with butyrate, in comparison to pure-culture growth with crotonate, were examined by one- and two-dimensional gel electrophoresis, and identified by peptide fingerprinting-mass spectrometry. A membrane-bound, externally oriented, quinone-linked formate dehydrogenase complex was expressed at high level specifically during syntrophic butyrate oxidation, comprising a selenocystein-linked catalytic subunit with a membrane-translocation pathway signal (TAT), a membrane-bound iron-sulfur subunit, and a membrane-bound cytochrome. Soluble hydrogenases were expressed at high levels specifically during growth with crotonate. The results were confirmed by native protein gel electrophoresis, by formate dehydrogenase and hydrogenase-activity staining, and by analysis of formate dehydrogenase and hydrogenase activities in intact cells and cell extracts. Furthermore, constitutive expression of a membrane-bound, internally oriented iron-sulfur oxidoreductase (DUF224) was confirmed, together with expression of soluble electron-transfer flavoproteins (EtfAB) and two previously identified butyryl-CoA dehydrogenases.Our findings allow to depict an electron flow scheme for syntrophic butyrate oxidation in S. wolfei. Electrons derived from butyryl-CoA are transferred through a membrane-bound EtfAB:quinone oxidoreductase (DUF224) to a menaquinone cycle and further via a b-type cytochrome to an externally oriented formate dehydrogenase. Hence, an ATP hydrolysis-driven proton-motive force across the cytoplasmatic membrane would provide the energy input for the electron potential shift necessary for formate formation.     

Metabolic properties and kinetics of methanogenic granules

Two types of mesophilic methanogenic granules (R- and F-granules) were developed on different synthetic feeds containing acetate, propionate and butyrate as major carbon sources and their metabolic properties were characterized. The metabolic activities of granules on acetate, formate and H₂-CO₂ were related to the feed composition used for their development. These granules performed a reversible reaction between H₂ production from formate and formate synthesis from H₂ plus bicarbonate. Both types of granules exhibited high activity on normal and branched volatile fatty acids with three to five carbons and low activity on ethanol and glucose. The granules performed a reversible isomerization between isobutyrate and butyrate during butyrate or isobutyrate degradation. Valerate and 2-methylbutyrate were produced and consumed during propionate-butyrate degradation. The respective apparent K _m (mm) for various substrates in disrupted R- and F-granules was: acetate, 0.43 and 0.41; propionate, 0.056 and 0.038; butyrate, 0.15 and 0.19; isobutyrate, 0.12 and 0.19; valerate, 0.15 and 0.098. Both granules had an optimum temperature range from 40 to 50° C for H₂-CO₂ and formate utilization and 40° C for acetate, propionate and butyrate utilization and a similar optimum pH. Correspondence to: J. G. Zeikus     

Methanogenesis at low temperatures by microflora of tundra wetland soil

Active methanogenesis from organic matter contained in soil samples from tundra wetland occurred even at 6 °C. Methane was the only end product in balanced microbial community with H₂/CO₂ as a substrate, besides acetate was produced as an intermediate at temperatures below 10°C. The activity of different microbial groups of methanogenic community in the temperature range of 6–28 °C was investigated using 5% of tundra soil as inoculum. Anaerobic microflora of tundra wetland fermented different organic compounds with formation of hydrogen, volatile fatty acids (VFA) and alcohols. Methane was produced at the second step. Homoacetogenic and methanogenic bacteria competed for such substrates as hydrogen, formate, carbon monoxide and methanol. Acetogens out competed methanogens in an excess of substrate and low density of microbial population. Kinetic analysis of the results confirmed the prevalence of hydrogen acetogenesis on methanogenesis. Pure culture of acetogenic bacteria was isolated at 6 °C. Dilution of tundra soil and supply with the excess of substrate disbalanced the methanoigenic microbial community. It resulted in accumulation of acetate and other VFA. In balanced microbial community obviously autotrophic methanogens keep hydrogen concentration below a threshold for syntrophic degradation of VFA. Accumulation of acetate- and H₂/CO₂-utilising methanogens should be very important in methanogenic microbial community operating at low temperatures.     

The genome of Syntrophorhabdus aromaticivorans strain UI provides new insights for syntrophic aromatic compound metabolism and electron flow

How aromatic compounds are degraded in various anaerobic ecosystems (e.g. groundwater, sediments, soils and wastewater) is currently poorly understood. Under methanogenic conditions (i.e. groundwater and wastewater treatment), syntrophic metabolizers are known to play an important role. This study explored the draft genome of Syntrophorhabdus aromaticivorans strain UI and identified the first syntrophic phenol‐degrading phenylphosphate synthase (PpsAB) and phenylphosphate carboxylase (PpcABCD) and syntrophic terephthalate‐degrading decarboxylase complexes. The strain UI genome also encodes benzoate degradation through hydration of the dienoyl‐coenzyme A intermediate as observed in Geobacter metallireducens and Syntrophus aciditrophicus. Strain UI possesses electron transfer flavoproteins, hydrogenases and formate dehydrogenases essential for syntrophic metabolism. However, the biochemical mechanisms for electron transport between these H₂/formate‐generating proteins and syntrophic substrate degradation remain unknown for many syntrophic metabolizers, including strain UI. Analysis of the strain UI genome revealed that heterodisulfide reductases (HdrABC), which are poorly understood electron transfer genes, may contribute to syntrophic H₂ and formate generation. The genome analysis further identified a putative ion‐translocating ferredoxin : NADH oxidoreductase (IfoAB) that may interact with HdrABC and dissimilatory sulfite reductase gamma subunit (DsrC) to perform novel electron transfer mechanisms associated with syntrophic metabolism.     

The effect of sulfate and nitrate on methane formation in a freshwater sediment

A freshwater sediment from a ditch of a peat grassland near Zegveld (Province of Utrecht, The Netherlands) was investigated for its potential methanogenic and syntrophic activity and the influence of sulfate and nitrate on these potential activities. Methanogenesis started after a 10 days lagphase. After 35–40 days aceticlastic methanogens were sufficiently enriched to cause a net decrease of acetate. In the presence of sulfate methane formation was only slightly affected. The addition of nitrate led to an outcompetion of aceticlastic methanogens by nitrate reducers. When inorganic electron acceptors were absent, substrates like propionate and butyrate were converted by syntrophic methanogenic consortia. Addition of inorganic electron acceptors resulted in an outcompetition of the syntrophic propionate and butyrate degrading consortia by the sulfate and nitrate reducers.     

Interspecies Electron Transfer during Propionate and Butyrate Degradation in Mesophilic, Granular Sludge

Granules from a mesophilic upflow anaerobic sludge blanket reactor were disintegrated, and bacteria utilizing only hydrogen or formate or both hydrogen and formate were added to investigate the role of interspecies electron transfer during degradation of propionate and butyrate. The data indicate that the major electron transfer occurred via interspecies hydrogen transfer, while interspecies formate transfer may not be essential for interspecies electron transfer in this system during degradation of propionate and butyrate.     

A genomic view on syntrophic versus non-syntrophic lifestyle in anaerobic fatty acid degrading communities

In sulfate-reducing and methanogenic environments complex biopolymers are hydrolyzed and degraded by fermentative micro-organisms that produce hydrogen, carbon dioxide and short chain fatty acids. Degradation of short chain fatty acids can be coupled to methanogenesis or to sulfate-reduction. Here we study from a genome perspective why some of these micro-organisms are able to grow in syntrophy with methanogens and others are not. Bacterial strains were selected based on genome availability and upon their ability to grow on short chain fatty acids alone or in syntrophic association with methanogens. Systematic functional domain profiling allowed us to shed light on this fundamental and ecologically important question. Extra-cytoplasmic formate dehydrogenases (InterPro domain number; IPR006443), including their maturation protein FdhE (IPR024064 and IPR006452) is a typical difference between syntrophic and non-syntrophic butyrate and propionate degraders. Furthermore, two domains with a currently unknown function seem to be associated with the ability of syntrophic growth. One is putatively involved in capsule or biofilm production (IPR019079) and a second in cell division, shape-determination or sporulation (IPR018365). The sulfate-reducing bacteria Desulfobacterium autotrophicum HRM2, Desulfomonile tiedjei and Desulfosporosinus meridiei were never tested for syntrophic growth, but all crucial domains were found in their genomes, which suggests their possible ability to grow in syntrophic association with methanogens. In addition, profiling domains involved in electron transfer mechanisms revealed the important role of the Rnf-complex and the formate transporter in syntrophy, and indicate that DUF224 may have a role in electron transfer in bacteria other than Syntrophomonas wolfei as well. This article is a part of a Special Issue entitled: 18th European Bioenergetics Conference (Biochim. Biophys. Acta, Volume 1837, Issue 7, July 2014).