Anaerobic degradation of propionate by a mesophilic acetogenic bacterium in coculture and triculture with different methanogens

A mesophilic acetogenic bacterium (MPOB) oxidized propionate to acetate and CO(2) in cocultures with the formate- and hydrogen-utilizing methanogens Methanospirillum hungatei and Methanobacterium formicicum. Propionate oxidation did not occur in cocultures with two Methanobrevibacter strains, which grew only with hydrogen. Tricultures consisting of MPOB, one of the Methanobrevibacter strains, and organisms which are able to convert formate into H(2) plus CO(2) (Desulfovibrio strain G11 or the homoacetogenic bacterium EE121) also degraded propionate. The MPOB, in the absence of methanogens, was able to couple propionate conversion to fumarate reduction. This propionate conversion was inhibited by hydrogen and by formate. Formate and hydrogen blocked the energetically unfavorable succinate oxidation to fumarate involved in propionate catabolism. Low formate and hydrogen concentrations are required for the syntrophic degradation of propionate by MPOB. In triculture with Methanospirillum hungatei and the aceticlastic Methanothrix soehngenii, propionate was degraded faster than in biculture with Methanospirillum hungatei, indicating that low acetate concentrations are favorable for propionate oxidation as well.

Enrichment of Thermophilic Propionate-Oxidizing Bacteria in Syntrophy with Methanobacterium thermoautotrophicum or Methanobacterium thermoformicicum

Thermophilic propionate-oxidizing, proton-reducing bacteria were enriched from the granular methanogenic sludge of a bench-scale upflow anaerobic sludge bed reactor operated at 55 degrees C with a mixture of volatile fatty acids as feed. Thermophilic hydrogenotrophic methanogens had a high decay rate. Therefore, stable, thermophilic propionate-oxidizing cultures could not be obtained by using the usual enrichment procedures. Stable and reproducible cultivation was possible by enrichment in hydrogen-pregrown cultures of Methanobacterium thermoautotrophicum DeltaH which were embedded in precipitates of FeS, achieved by addition of FeCl(2) to the media. The propionate-oxidizing bacteria formed spores which resisted pasteurization for 30 min at 90 degrees C or 10 min at 100 degrees C. Highly purified cultures were obtained with either M. thermoautotrophicum DeltaH or Methanobacterium thermoformicicum Z245 as the syntrophic partner organism. The optimum temperature for the two cultures was 55 degrees C. Maximum specific growth rates of cultures with M. thermoautotrophicum DeltaH were somewhat lower than those of cultures with M. thermoformicicum Z245 (0.15 and 0.19 day, respectively). Growth rates were even higher (0.32 day) when aceticlastic methanogens were present as well. M. thermoautotrophicum DeltaH is an obligately hydrogen-utilizing methanogen, showing that interspecies hydrogen transfer is the mechanism by which reducing equivalents are channelled from the acetogens to this methanogen. Boundaries of hydrogen partial pressures at which propionate oxidation occurred were between 6 and 34 Pa. Formate had a strong inhibitory effect on propionate oxidation in cultures with M. thermoautotrophicum. Inhibition by formate was neutralized by addition of the formate-utilizing methanogen or by addition of fumarate. Results indicate that formate inhibited succinate oxidation to fumarate, an intermediate step in the biochemical pathway of propionate oxidation.

Regulation of Product Formation in Bacteroides xylanolyticus X5-1 by Interspecies Electron Transfer

Bacteroides xylanolyticus X5-1 was grown in pure culture and in mixed culture with Methanospirillum hungatei JF-1 under xylose limitation in the chemostat. In the pure culture, ethanol, acetate, CO(2), and hydrogen were the products. In the mixed culture, acetate, CO(2), and presumably hydrogen were the only products formed by B. xylanolyticus X5-1. The biomass yield of B. xylanolyticus X5-1 increased because of cocultivation. In cell extracts of the pure culture, both NAD- and NADP-dependent acetaldehyde dehydrogenase and ethanol dehydrogenase activities were found. In cell extracts of the mixed culture, activities of these enzymes were not detected. Inhibition of methanogenesis in the mixed culture by the addition of bromoethanosulfonic acid (BES) resulted in an accumulation of H(2), ethanol, and formate. Immediately after the addition of BES, NAD-dependent acetaldehyde dehydrogenase and ethanol dehydrogenase activities were detected. After a short lag phase, a NADP-dependent ethanol dehydrogenase was also detectable. The induction of acetaldehyde dehydrogenase and ethanol dehydrogenase was inhibited by chloramphenicol, suggesting de novo synthesis of these enzymes. These results are consistent with a model in which the shift in product formation caused by interspecies electron transfer is regulated at the level of enzyme synthesis.

Hydrophobicities and electrophoretic mobilities of anaerobic bacterial isolates from methanogenic granular sludge

The hydrophobicities and electrophoretic mobilities of isolates from methanogenic anaerobic granular sludge were measured and compared with those of strains from culture collections. All new isolates were highly hydrophobic, indicating that the upflow anaerobic sludge blanket reactor concept selects for hydrophobic bacteria. Methanothrix soehngenii, a methanogen often observed in methanogenic granular sludge, was highly hydrophobic and showed low electrophoretic mobility at pH 7. The role of this strain in the formation of methanogenic granular sludge is discussed.

Growth of syntrophic propionate-oxidizing bacteria with fumarate in the absence of methanogenic bacteria

Oxidation of succinate to fumarate is an energetically difficult step in the biochemical pathway of propionate oxidation by syntrophic methanogenic cultures. Therefore, the effect of fumarate on propionate oxidation by two different propionate-oxidizing cultures was investigated. When the methanogens in a newly enriched propionate-oxidizing methanogenic culture were inhibited by bromoethanesulfonate, fumarate could act as an apparent terminal electron acceptor in propionate oxidation. C-nuclear magnetic resonance experiments showed that propionate was carboxylated to succinate while fumarate was partly oxidized to acetate and partly reduced to succinate. Fumarate alone was fermented to succinate and CO(2). Bacteria growing on fumarate were enriched and obtained free of methanogens. Propionate was metabolized by these bacteria when either fumarate or Methanospirillum hungatii was added. In cocultures with Syntrophobacter wolinii, such effects were not observed upon addition of fumarate. Possible slow growth of S. wolinii on fumarate could not be demonstrated because of the presence of a Desulfovibrio strain which grew rapidly on fumarate in both the absence and presence of sulfate.

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.

Detection and quantification of microorganisms in anaerobic bioreactors

The presence of sulfate in anaerobic reactors can trigger competitive and syntrophic interactions between various groups of microorganisms, such as sulfate reducers, methanogens and acetogens. In order to steer the reactor process in the direction of sulfidogenesis or methanogenesis, it is essential to get insight into the population dynamics of these groups of microorganisms upon changes in the reactor operating conditions. Several methods exist to characterize and quantify the microbial sludge composition. Combining classical microbiological and modern molecular-based sludge characterization methods has proven to be a powerful approach to study the microbial composition of the anaerobic sludge.

ADP-dependent phosphofructokinases in mesophilic and thermophilic methanogenic archaea

Phosphofructokinase (PFK) is a key enzyme of the glycolytic pathway in all domains of life. Two related PFKs, ATP-dependent and PP(i)-dependent PFK, have been distinguished in bacteria and eucarya, as well as in some archaea. Hyperthermophilic archaea of the order Thermococcales, including Pyrococcus and Thermococcus spp., have recently been demonstrated to possess a unique ADP-dependent PFK (ADP-PFK) that appears to be phylogenetically distinct. Here, we report the presence of ADP-PFKs in glycogen-producing members of the orders Methanococcales and Methanosarcinales, including both mesophilic and thermophilic representatives. To verify the substrate specificities of the methanogenic kinases, the gene encoding the ADP-PFK from Methanococcus jannaschii was functionally expressed in Escherichia coli, and the produced enzyme was purified and characterized in detail. Compared to its counterparts from the two members of the order Thermococcales, the M. jannaschii ADP-PFK has an extremely low K(m) for fructose 6-phosphate (9.6 microM), and it accepts both ADP and acetyl-phosphate as phosphoryl donors. Phylogenetic analysis of the ADP-PFK reveals it to be a key enzyme of the modified Embden-Meyerhof pathway of heterotrophic and chemolithoautotrophic archaea. Interestingly, uncharacterized homologs of this unusual kinase are present in several eucarya.

Performance of a thermophilic sulfate and sulfite reducing high rate anaerobic reactor fed with methanol

Thermophilic sulfate and sulfite reduction was studied in lab-scale Expanded Granular Sludge Bed (EGSB) reactors operated at 65 degrees C and pH 7.5 with methanol as the sole carbon and energy source for the sulfate- and sulfite-reducing bacteria. At a hydraulic retention time (HRT) of 10 h, maximum sulfite and sulfate elimination rates of 5.5 g SO3(2-) L(-1) day(-1) (100% elimination) and 5.7 g SO4(2-) L(-1) day(-1) (55% elimination) were achieved, resulting in an effluent sulfide concentration of approximately 1800 mg S L(-1). Sulfate elimination was limited by the sulfide concentration, as stripping of H2S from the reactor with nitrogen gas was found to increase the sulfate elimination rate to 9.9 g SO4(2-) L(-1) day(-1) (100% elimination). At a HRT of 3 h, maximum achievable sulfite and sulfate elimination rates were even 18 g SO3(2-) L(-1) day(-1) (100% elimination) and 11 g SO4(2-) L(-1) day(-1) (50% elimination). At a HRT of 3 h, the elimination rate was limited by the biomass retention of the system. 5.5 +/- 1.8% of the consumed methanol was converted to acetate, which was not further degraded by sulfate reducing bacteria present in the sludge. The acetotrophic activity of the sludge could not be stimulated by cultivating the sludge for 30 days under methanol-limiting conditions. Omitting cobalt as trace element from the influent resulted in a lower acetate production rate, but it also led to a lower sulfate reduction rate. Sulfate degradation in the reactor could be described by zeroth order kinetics down to a threshold concentration of 0.05 g L(-1), while methanol degradation followed Michaelis-Menten kinetics with a Km of 0.037 g COD L(-1).

Two distinct enzyme systems are responsible for tetrachloroethene and chlorophenol reductive dehalogenation in Desulfitobacterium strain PCE1

Desulfitobacterium strain PCE1 is able to use tetrachloroethene and chloroaromatics as terminal electron acceptors for growth. Cell extracts of Desulfitobacterium strain PCE1 grown with tetrachloroethene as electron acceptor showed no dehalogenase activity with 3-chloro-4-hydroxyphenylacetate (Cl-OH-phenylacetate) and other ortho-chlorophenolic compounds in an in vitro assay. Extracts of cells that were grown with Cl-OH-phenylacetate as electron acceptor dechlorinated tetrachloroethene at 10% of the dechlorination rate of Cl-OH-phenylacetate. In both cell extracts dechlorination was inhibited by the addition of 1-iodopropane and dinitrogen oxide, inhibitors of cobalamin-containing enzymes. The enzymes responsible for tetrachloroethene and Cl-OH-phenylacetate dechlorination were partially purified. A 100-fold enriched fraction of chlorophenol reductive dehalogenase was obtained that mainly contained a protein with a subunit size of 48 kDa. The characteristics of this enzyme are similar to that of the chlorophenol reductive dehalogenase of D. dehalogenans. After partial purification of the tetrachloroethene reductive dehalogenase, a fraction was obtained that also contained a 48-kDa protein, but the N-terminal sequence showed no similarity with that of the chlorophenol reductive dehalogenase sequence or with the N-terminal amino acid sequence of tetra- and trichloroethene reductive dehalogenase of Desulfitobacterium strain TCE1. These results provide strong evidence that two different enzymes are responsible for tetrachloroethene and chlorophenol dechlorination in Desulfitobacterium strain PCE1. Furthermore, the characterization of partially purified tetrachloroethene reductive dehalogenase indicated that this enzyme is a novel type of reductive dehalogenase.

Energy yield of respiration on chloroaromatic compounds in Desulfitobacterium dehalogenans

The amount of energy that can be conserved via halorespiration by Desulfitobacterium dehalogenans JW/IU-DC1 was determined by comparison of the growth yields of cells grown with 3-chloro-4-hydroxyphenyl acetate (Cl-OHPA) and different electron donors. Cultures that were grown with lactate, pyruvate, formate, or hydrogen as an electron donor and Cl-OHPA as an electron acceptor yielded 3.1, 6.6, 1.6, and 1.6 g (dry weight) per mol of reduction equivalents, respectively. Fermentative growth on pyruvate yielded 14 g (dry weight) per mol of pyruvate oxidized. Pyruvate was not fermented stoichiometrically to acetate and lactate, but an excess of acetate was produced. Experiments with 13C-labeled bicarbonate showed that during pyruvate fermentation, approximately 9% of the acetate was formed from the reduction of CO2. Comparison of the growth yields suggests that 1 mol of ATP is produced per mol of acetate produced by substrate-level phosphorylation and that there is no contribution of electron transport phosphorylation when D. dehalogenans grows on lactate plus Cl-OHPA or pyruvate plus Cl-OHPA. Furthermore, the growth yields indicate that approximately 1/3 mol of ATP is conserved per mol of Cl-OHPA reduced in cultures grown in formate plus Cl-OHPA and hydrogen plus Cl-OHPA. Because neither formate nor hydrogen nor Cl-OHPA supports substrate-level phosphorylation, energy must be conserved through the establishment of a proton motive force. Pyruvate ferredoxin oxidoreductase, lactate dehydrogenase, formate dehydrogenase, and hydrogenase were localized by in vitro assays with membrane-impermeable electron acceptors and donors. The orientation of chlorophenol-reductive dehalogenase in the cytoplasmic membrane, however, could not be determined. A model is proposed, which may explain the topology analyses as well as the results obtained in the yield study.

Elucidation of the pathways of catabolic glutamate conversion in three thermophilic anaerobic bacteria

The glutamate catabolism of three thermophilic syntrophic anaerobes was compared based on the combined use of [(13)C] glutamate NMR measurements and enzyme activity determinations. In some cases the uptake of intermediates from different pathways was studied. The three organisms, Caloramator coolhaasii, Thermanaerovibrio acidaminovorans and strain TGO, had a different stoichiometry of glutamate conversion and were dependent on the presence of a hydrogen scavenger (Methanobacterium thermoautotrophicum Z245) to a different degree for their growth. C. coolhaasii formed acetate, CO(2), NH(4)(+) and H(2) from glutamate. Acetate was found to be formed through the beta-methylaspartate pathway in pure culture as well as in coculture. T. acidaminovorans converted glutamate to acetate, propionate, CO(2), NH(4)(+) and H(2). Most likely, this organism uses the beta-methylaspartate pathway for acetate formation. Propionate formation occurred through a direct oxidation of glutamate via succinyl-CoA and methylmalonyl-CoA. The metabolism of T. acidaminovorans shifted in favour of propionate formation when grown in coculture with the methanogen, but this did not lead to the use of a different glutamate degradation pathway. Strain TGO, an obligate syntrophic glutamate-degrading organism, formed propionate, traces of succinate, CO(2), NH(4)(+) and H(2). Glutamate was converted to propionate oxidatively via the intermediates succinyl-CoA and methylmalonyl-CoA. A minor part of the succinyl-CoA was converted to succinate and excreted.

A Desulfitobacterium strain isolated from human feces that does not dechlorinate chloroethenes or chlorophenols

An anaerobic bacterium, strain DP7, was isolated from human feces in mineral medium with formate and 0.02% yeast extract as energy and carbon source. This rod-shaped motile bacterium used pyruvate, lactate, formate, hydrogen, butyrate, and ethanol as electron donor for sulfite reduction. Other electron acceptors such as thiosulfate, nitrate and fumarate stimulated growth in the presence of 0.02% yeast extract and formate. Acetate was the only product during fermentative growth on pyruvate. Six mol of pyruvate were fermented to 7 mol of acetate. 13C-NMR labeling experiments showed homoacetogenic 13C-CO2 incorporation into acetate. The pH and temperature optimum of fermentative growth on pyruvate was 7.4 and 37 degrees C, respectively. The growth rate under these conditions was approximately 0.10 h(-1). Strain DP7 was identified as a new strain of Desulfitobacterium frappieri on the basis of 16S rRNA sequence analysis (99% similarity) and DNA-DNA hybridization (reassociation value of 83%) with Desulfitobacterium frappieri TCE1. In contrast to described Desulfitobacterium strains, the newly isolated strain has not been isolated from a polluted environment and did not use chloroethenes or chlorophenols as electron acceptor.

Constitutive dechlorination of chlorinated ethenes by a methanol degrading methanogenic consortium

The ability of granular methanogenic sludge to dechlorinate chloroethenes was investigated with unadapted sludge from an upflow anaerobic sludge blanket (UASB) reactor fed with methanol. The sludge degraded chlorinated ethenes, but the degradation rates were low. The addition of primary substrate was necessary to sustain dechlorination. The dechlorinating activity seemed to be constitutively present in the anaerobic bacteria. Usually, one chlorine atom was removed via reductive hydrogenolysis. Only trichloroethene (TCE) was converted to substantial amounts of vinylchloride (VC). 1,1-Dichloroethene (1,1DCE) was observed to be an important intermediate in the dechlorination by unadapted granular sludge, although previously this compound had not been commonly observed. Furthermore, the dechlorination of 1,1DCE was faster than the dechlorination of the other chloroethenes.

Pathway of propionate oxidation by a syntrophic culture of Smithella propionica and Methanospirillum hungatei

The pathway of propionate conversion in a syntrophic coculture of Smithella propionica and Methanospirillum hungatei JF1 was investigated by (13)C-NMR spectroscopy. Cocultures produced acetate and butyrate from propionate. [3-(13)C]propionate was converted to [2-(13)C]acetate, with no [1-(13)C]acetate formed. Butyrate from [3-(13)C]propionate was labeled at the C2 and C4 positions in a ratio of about 1:1.5. Double-labeled propionate (2,3-(13)C) yielded not only double-labeled acetate but also single-labeled acetate at the C1 or C2 position. Most butyrate formed from [2,3-(13)C]propionate was also double labeled in either the C1 and C2 atoms or the C3 and C4 atoms in a ratio of about 1:1.5. Smaller amounts of single-labeled butyrate and other combinations were also produced. 1-(13)C-labeled propionate yielded both [1-(13)C]acetate and [2-(13)C]acetate. When (13)C-labeled bicarbonate was present, label was not incorporated into acetate, propionate, or butyrate. In each of the incubations described above, (13)C was never recovered in bicarbonate or methane. These results indicate that S. propionica does not degrade propionate via the methyl-malonyl-coenzyme A (CoA) pathway or any other of the known pathways, such as the acryloyl-CoA pathway or the reductive carboxylation pathway. Our results strongly suggest that propionate is dismutated to acetate and butyrate via a six-carbon intermediate.

Arginine catabolism by Thermanaerovibrio acidaminovorans

The arginine catabolism of Thermanaerovibrio acidaminovorans was investigated. T. acidaminovorans was able to produce approximately 0.4--0.5 mol citrulline and 0.5--0.6 mol ornithine from 1 mol of arginine. However, in a methanogenic coculture with Methanobacterium thermoautotrophicum Z245 1 mol arginine was converted to approximately 1 mol of propionate, 0.5 mol acetate, 4 mol ammonia and 4 mol hydrogen; citrulline and ornithine were not formed. Enzyme measurements indicated the presence of the arginine deiminase pathway (ADI) in cells of T. acidaminovorans growing on arginine.

The effect of oxygen on methanol oxidation by an obligate methanotrophic bacterium studied by in vivo 13C nuclear magnetic resonance spectroscopy

13C NMR was used to study the effect of oxygen on methanol oxidation by a type II methanotrophic bacterium isolated from a bioreactor in which methane was used as electron donor for denitrification. Under high (35-25%) oxygen conditions the first step of methanol oxidation to formaldehyde was much faster than the following conversions to formate and carbon dioxide. Due to this the accumulation of formaldehyde led to a poisoning of the cells. A more balanced conversion of 13C-labelled methanol to carbon dioxide was observed at low (1-5%) oxygen concentrations. In this case, formaldehyde was slowly converted to formate and carbon dioxide. Formaldehyde did not accumulate to inhibitory levels. The oxygen-dependent formation of formaldehyde and formate from methanol is discussed kinetically and thermodynamically.

Methanol conversion in high-rate anaerobic reactors

An overview on methanol conversion in high-rate anaerobic reactors is presented, with the focus on technological as well as microbiological aspects. The simple C1-compound methanol can be degraded anaerobically in a complex way, in which methanogens, sulfate reducing bacteria and homoacetogens interact cooperatively or competitively at substrate level. This interaction has large technological implications as it determines the final product of methanol mineralization, methane or carbon dioxide. The degradation route of methanol may be entirely different when environmental conditions change. Direct methanogenesis from methanol seems the predominant mineralization route under mesophilic conditions both in the absence and the presence of sulfate. Under thermophilic conditions methanol oxidation to carbon dioxide and hydrogen appears to play an important role. The UASB technology for mesophilic digestion of methanolic waste has presently reached full-scale maturity. The potential of methanol as feedstock for anaerobic processes is discussed.

New developments in reactor and process technology for sulfate reduction

Sulfate reduction has been regarded in the past as an unwanted process in anaerobic treatment of sulfate-rich wastewaters. Research efforts were primarily focused on H2S toxicity, competition between sulfidogenic and methanogenic microorganisms and suppression of sulfidogenesis. More recently, the potential sulfidogenesis for treating a wide range of wastestreams contaminated with oxidized sulfurous compounds and/or heavy metals was also appreciated. Heavy metals can be removed by the formation and subsequent precipitation of poorly soluble metal sulfides. Basically two approaches can be distinguished in wastewater treatment: passive treatment using low-cost technologies and active treatment in newly developed bioreactors. Both strategies are discussed.

Intracellular PHB conversion in a Type II methanotroph studied by 13C NMR

Poly-p-hydroxybutyrate (PHB) formation under aerobic conditions via incorporation of [13C-2]acetate as a cosubstrate and its intracellular degradation under anaerobic conditions in a Type II methanotroph was studied by 13C NMR. During PHB synthesis in the presence of labelled acetate, low levels of beta-hydroxybutyrate, butyrate, acetone, isopropanol, 2,3-butanediol and succinate were observed. Subsequent anaerobic PHB breakdown showed enhanced levels of these products at the expense of PHB. Fermentative metabolism occurring during anaerobic PHB degradation was confirmed in experiments with fully 13C-enriched cells, which were grown on 13C-labelled methane. beta-hydroxybutyrate, butyrate, acetate, acetone, isopropanol, 2,3-butanediol and succinate were detected as multiple 13C-labelled compounds in the culture medium. Our results suggest that intracellular PHB degradation can be used as a reserve energy source by methanotrophs under anoxic conditions.

Denitrification with methane as electron donor in oxygen-limited bioreactors

The microbial population from a reactor using methane as electron donor for denitrification under microaerophilic conditions was analyzed. High numbers of aerobic methanotrophic bacteria (3 10(7) cells/ml) and high numbers of acetate-utilizing denitrifying bacteria (2 10(7) cells/ml) were detected, but only very low numbers of methanol-degrading denitrifying bacteria (4 10(4) cells/ml) were counted. Two abundant acetate-degrading denitrifiers were isolated which, based on 16S rRNA analysis, were closely related to Mesorhizobium plurifarium (98.4% sequence similarity) and a Stenotrophomonas sp. (99.1% sequence similarity). A methanol-degrading denitrifying bacterium isolated from the bioreactor morphologically resembled Hyphomicrobium sp. and was moderately related to H. vulgare (93.5% sequence similarity). The initial characterization of the most abundant methanotrophic bacterium indicated that it belongs to class II of the methanotrophs. "In vivo" 13C-NMR with concentrated cell suspensions showed that this methanotroph produced acetate under oxygen limitation. The microbial composition of reactor material together with the NMR experiments suggest that in the reactor methanotrophs excrete acetate, which serves as the direct electron donor for denitrification.

Caloramator coolhaasii sp. nov., a glutamate-degrading, moderately thermophilic anaerobe

An obligately anaerobic, moderately thermophilic, glutamate-degrading bacterium (strain ZT) was isolated from an enrichment culture obtained from anaerobic thermophilic granular sludge. The cells were rod-shaped to filamentous and showed no motility or spore formation. The cell wall had a Gram-positive structure, which was revealed by electron microscopy. Optimum growth of the strain was observed under neutrophilic conditions at 50-55 degrees C. The doubling time of strain ZT grown in rich medium was approximately 1 h at optimal pH and temperature. Strain ZT was able to grow on a variety of organic compounds. Most carbon sources were converted to acetate, CO2, H2, and traces of propionate and lactate. Strain ZT oxidized glutamate to acetate, CO2, NH4+, traces of propionate and H2. The doubling time on this substrate was 1-6 d. The strain fermented glutamate syntrophically in co-culture with Methanobacterium thermoautotrophicum Z-245T to the same products, but the co-culture had a fourfold higher growth rate. 16S rDNA sequence analysis revealed a relationship with Thermobrachium celere, Caloramator indicus and Caloramator proteoclasticus. The G+C content was 31.7 mol%. Based on its morphological, phylogenetic and physiological characteristics, it is proposed that strain ZT should be classified in the genus Caloramator as a new species, Caloramator coolhaasii.

Effect of 2-bromo-ethane sulfonate, molybdate and chloroform on acetate consumption by methanogenic and sulfate-reducing populations in freshwater sediment

The relative importance of methanogenesis and sulfate reduction in freshwater sediment supplemented with acetate was investigated. Addition of acetate stimulated both methane formation and sulfate reduction, indicating that an active aceticlastic population of methanogens and sulfate reducers was present in the sediment. Sulfate reducers were most important in the consumption of acetate. However, when sulfate reducers were inhibited, acetate was metabolised at a similar rate by methanogens. Acetate, propionate and valerate accumulated only when both processes were inhibited by the combined addition of 2-bromo-ethane sulfonate and molybdate. The relative amounts of acetate, propionate and valerate were 93, 6 and 1 mol%, respectively. These results demonstrate the role of acetate as a key intermediate in the terminal step of organic matter mineralisation in the sediment. Addition of chloroform inhibited both methanogenesis and sulfate reduction. We studied the inhibitory effect of CHCl(3) on homoacetogenic bacteria, sulfate-reducing bacteria and methanogens. The results showed that inhibition by CHCl(3) correlates with microorganisms, which operate the acetyl-CoA cleavage pathway. We propose that chloroform can be used to elucidate the role of different metabolic types of sulfate reducers to sulfate reduction in natural environments.

Kinetics of syntrophic cultures: a theoretical treatise on butyrate fermentation

Numerous microbial conversions in methanogenic environments proceed at (Gibbs) free energy changes close to thermodynamic equilibrium. In this paper we attempt to describe the consequences of this thermodynamic boundary condition on the kinetics of anaerobic conversions in methanogenic environments. The anaerobic fermentation of butyrate is used as an example. Based on a simple metabolic network stoichiometry, the free energy change based balances in the cell, and the flux of substrates and products in the catabolic and anabolic reactions are coupled. In butyrate oxidation, a mechanism of ATP-dependent reversed electron transfer has been proposed to drive the unfavorable oxidation of butyryl-CoA to crotonyl-CoA. A major assumption in our model is that ATP-consumption and electron translocation across the cytoplasmic membrane do not proceed according to a fixed stoichiometry, but depend on the cellular concentration ratio of ATP and ADP. The energetic and kinetic impact of product inhibition by acetate and hydrogen are described. A major consequence of the derived model is that Monod-based kinetic description of this type of conversions is not feasible, because substrate conversion and biomass growth are proposed to be uncoupled. It furthermore suggests that the specific substrate conversion rate cannot be described as a single function of the driving force of the catabolic reaction but depends on the actual substrate and product concentrations. By using nonfixed stoichiometries for the membrane associated processes, the required flexibility of anaerobic bacteria to adapt to varying environmental conditions can be described.

Thermophilic sulfate reduction and methanogenesis with methanol in a high rate anaerobic reactor

Sulfate reduction outcompeted methanogenesis at 65 degrees C and pH 7.5 in methanol and sulfate-fed expanded granular sludge bed reactors operated at hydraulic retention times (HRT) of 14 and 3.5 h, both under methanol-limiting and methanol-overloading conditions. After 100 and 50 days for the reactors operated at 14 and 3.5 h, respectively, sulfide production accounted for 80% of the methanol-COD consumed by the sludge. The specific methanogenic activity on methanol of the sludge from a reactor operated at HRTs of down to 3.5 h for a period of 4 months gradually decreased from 0. 83 gCOD. gVSS(-1). day(-1) at the start to a value of less than 0.05 gCOD. gVSS(-1). day(-1), showing that the relative number of methanogens decreased and eventually became very low. By contrast, the increase of the specific sulfidogenic activity of sludge from 0. 22 gCOD. gVSS(-1). day(-1) to a final value of 1.05 gCOD. gVSS(-1). day(-1) showed that sulfate reducing bacteria were enriched. Methanol degradation by a methanogenic culture obtained from a reactor by serial dilution of the sludge was inhibited in the presence of vancomycin, indicating that methanogenesis directly from methanol was not important. H(2)/CO(2) and formate, but not acetate, were degraded to methane in the presence of vancomycin. These results indicated that methanol degradation to methane occurs via the intermediates H(2)/CO(2) and formate. The high and low specific methanogenic activity of sludge on H(2)/CO(2) and formate, respectively, indicated that the former substrate probably acts as the main electron donor for the methanogens during methanol degradation. As sulfate reduction in the sludge was also strongly supported by hydrogen, competition between sulfate reducing bacteria and methanogens in the sludge seemed to be mainly for this substrate. Sulfate elimination rates of up to 15 gSO(4)(2-)/L per day were achieved in the reactors. Biomass retention limited the sulfate elimination rate.

Purification and characterization of (per)chlorate reductase from the chlorate-respiring strain GR-1

Strain GR-1 is one of several recently isolated bacterial species that are able to respire by using chlorate or perchlorate as the terminal electron acceptor. The organism performs a complete reduction of chlorate or perchlorate to chloride and oxygen, with the intermediate formation of chlorite. This study describes the purification and characterization of the key enzyme of the reductive pathway, the chlorate and perchlorate reductase. A single enzyme was found to catalyze both the chlorate- and perchlorate-reducing activity. The oxygen-sensitive enzyme was located in the periplasm and had an apparent molecular mass of 420 kDa, with subunits of 95 and 40 kDa in an alpha(3)beta(3) composition. Metal analysis showed the presence of 11 mol of iron, 1 mol of molybdenum, and 1 mol of selenium per mol of heterodimer. In accordance, quantitative electron paramagnetic resonance spectroscopy showed the presence of one [3Fe-4S] cluster and two [4Fe-4S] clusters. Furthermore, two different signals were ascribed to Mo(V). The K(m) values for perchlorate and chlorate were 27 and <5 microM, respectively. Besides perchlorate and chlorate, nitrate, iodate, and bromate were also reduced at considerable rates. The resemblance of the enzyme to nitrate reductases, formate dehydrogenases, and selenate reductase is discussed.

Molecular and biochemical characterization of the ADP-dependent phosphofructokinase from the hyperthermophilic archaeon Pyrococcus furiosus

Pyrococcus furiosus uses a modified Embden-Meyerhof pathway involving two ADP-dependent kinases. Using the N-terminal amino acid sequence of the previously purified ADP-dependent glucokinase, the corresponding gene as well as a related open reading frame were detected in the genome of P. furiosus. Both genes were successfully cloned and expressed in Escherichia coli, yielding highly thermoactive ADP-dependent glucokinase and phosphofructokinase. The deduced amino acid sequences of both kinases were 21.1% identical but did not reveal significant homology with those of other known sugar kinases. The ADP-dependent phosphofructokinase was purified and characterized. The oxygen-stable protein had a native molecular mass of approximately 180 kDa and was composed of four identical 52-kDa subunits. It had a specific activity of 88 units/mg at 50 degrees C and a pH optimum of 6.5. As phosphoryl group donor, ADP could be replaced by GDP, ATP, and GTP to a limited extent. The K(m) values for fructose 6-phosphate and ADP were 2.3 and 0.11 mM, respectively. The phosphofructokinase did not catalyze the reverse reaction, nor was it regulated by any of the known allosteric modulators of ATP-dependent phosphofructokinases. ATP and AMP were identified as competitive inhibitors of the phosphofructokinase, raising the K(m) for ADP to 0.34 and 0.41 mM, respectively.

Purification and molecular characterization of ortho-chlorophenol reductive dehalogenase, a key enzyme of halorespiration in Desulfitobacterium dehalogenans

ortho-Chlorophenol reductive dehalogenase of the halorespiring Gram-positive Desulfitobacterium dehalogenans was purified 90-fold to apparent homogeneity. The purified dehalogenase catalyzed the reductive removal of a halogen atom from the ortho position of 3-chloro-4-hydroxyphenylacetate, 2-chlorophenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, pentachlorophenol, and 2-bromo-4-chlorophenol with reduced methyl viologen as electron donor. The dechlorination of 3-chloro-4-hydroxyphenylacetate was catalyzed by the enzyme at a Vmax of 28 units/mg protein and a Km of 20 microM. The pH and temperature optimum were 8.2 and 52 degrees C, respectively. EPR analysis indicated one [4Fe-4S] cluster (midpoint redox potential (Em) = -440 mV), one [3Fe-4S] cluster (Em = +70 mV), and one cobalamin per 48-kDa monomer. The Co(I)/Co(II) transition had an Em of -370 mV. Via a reversed genetic approach based on the N-terminal sequence, the corresponding gene was isolated from a D. dehalogenans genomic library, cloned, and sequenced. This revealed the presence of two closely linked genes: (i) cprA, encoding the o-chlorophenol reductive dehalogenase, which contains a twin-arginine type signal sequence that is processed in the purified enzyme; (ii) cprB, coding for an integral membrane protein that could act as a membrane anchor of the dehalogenase. This first biochemical and molecular characterization of a chlorophenol reductive dehalogenase has revealed structural resemblance with haloalkene reductive dehalogenases.

Reductive dechlorination of tetrachloroethene to cis-1, 2-dichloroethene by a thermophilic anaerobic enrichment culture

Thermophilic anaerobic biodegradation of tetrachloroethene (PCE) was investigated with various inocula from geothermal and nongeothermal areas. Only polluted harbor sediment resulted in a stable enrichment culture that converted PCE via trichloroethene to cis-1, 2-dichloroethene at the optimum temperature of 60 to 65 degrees C. After several transfers, methanogens were eliminated from the culture. Dechlorination was supported by lactate, pyruvate, fructose, fumarate, and malate as electron donor but not by H2, formate, or acetate. Fumarate and L-malate led to the highest dechlorination rate. In the absence of PCE, fumarate was fermented to acetate, H2, CO2, and succinate. With PCE, less H2 was formed, suggesting that PCE competed for the reducing equivalents leading to H2. PCE dechlorination, apparently, was not outcompeted by fumarate as electron acceptor. At the optimum dissolved PCE concentration of approximately 60 microM, a high dechlorination rate of 1.1 micromol h-1 mg-1 (dry weight) was found, which indicates that the dechlorination is not a cometabolic activity. Microscopic analysis of the fumarate-grown culture showed the dominance of a long thin rod. Molecular analysis, however, indicated the presence of two dominant species, both belonging to the low-G+C gram positives. The highest similarity was found with the genus Dehalobacter (90%), represented by the halorespiring organism Dehalobacter restrictus, and with the genus Desulfotomaculum (86%).

High-rate anaerobic treatment of wastewater at low temperatures

Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8 degrees C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids-1 day-1, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40 degrees C.

Desulfobacca acetoxidans gen. nov., sp. nov., a novel acetate-degrading sulfate reducer isolated from sulfidogenic granular sludge

A mesophilic sulfate reducer, strain ASRB2T, was isolated with acetate as sole carbon and energy source from granular sludge of a laboratory-scale upflow anaerobic sludge bed reactor fed with acetate and sulfate. The bacterium was oval-shaped, 1.3 x 1.9-2.2 microns, non-motile and Gram-negative. Optimum growth with acetate occurred around 37 degrees C in freshwater medium (doubling time: 1.7-2.2 d). Enzyme studies indicated that acetate was oxidized via the carbon monoxide dehydrogenase pathway. Growth was not supported by other organic acids, such as propionate, butyrate or lactate, alcohols such as ethanol or propanol, and hydrogen or formate. Sulfite and thiosulfate were also used as electron acceptors, but sulfur and nitrate were not reduced. Phylogenetically, strain ASRB2T clustered with the delta subclass of the Proteobacteria. Its closest relatives were Desulfosarcina variabilis, Desulfacinum infernum and Syntrophus buswellii. Strain ASRB2T is described as the type strain of Desulfobacca acetoxidans gen. nov., sp. nov.

13C-NMR study of propionate metabolism by sludges from bioreactors treating sulfate and sulfide rich wastewater

Applications of nuclear magnetic resonance (NMR) to study a variety of physiological and biochemical aspects of bacteria with a role in the sulfur cycle are reviewed. Then, a case-study of high resolution 13C-NMR spectroscopy on sludges from bioreactors used for treating sulfate and sulfide rich wastewaters is presented. 13C-NMR was used to study the effect of sulfate and butyrate on propionate conversion by mesophilic anaerobic (methanogenic and sulfate reducing) granular sludge and microaerobic (sulfide oxidizing) flocculant sludge. In the presence of sulfate, propionate was degraded via the randomising pathway in all sludge types investigated. This was evidenced by scrambling of [3-13C]propionate into [2-13C]propionate and the formation of acetate equally labeled in the C1 and C2 position. In the absence of sulfate, [3-13C]propionate scrambled to a lesser extend without being degraded further. Anaerobic sludges converted [2,3-13C]propionate partly into the higher fatty acid 2-methyl[2,3-13C]butyrate during the simultaneous degradation of [2,3-13C]propionate and butyrate. [4,5-13C]valerate was also formed in the methanogenic sludges. Up to 10% of the propionate present was converted via these alternative degradation routes. Labeled butyrate was not detected in the incubations, suggesting that reductive carboxylation of propionate does not occur in the sludges.

Anaerobic treatment of sulphate-rich wastewaters

Until recently, biological treatment of sulphate-rich wastewater was rather unpopular because of the production of H2S under anaerobic conditions. Gaseous and dissolved sulphides cause physical-chemical (corrosion, odour, increased effluent chemical oxygen demand) or biological (toxicity) constraints, which may lead to process failure. Anaerobic treatment of sulphate-rich wastewater can nevertheless be applied successfully provided a proper treatment strategy is selected. The strategies currently available are discussed in relation to the aim of the treatment: i) removal of organic matter, ii) removal of sulphate or iii) removal of both. Also a whole spectrum of new biotechnological applications (removal of organic chemical oxygen demand, sulphur, nitrogen and heavy metals), recently developed based on a better insight in sulphur transformations, are discussed.

Syntrophobacter fumaroxidans sp. nov., a syntrophic propionate-degrading sulfate-reducing bacterium

A syntrophic propionate-oxidizing bacterium, strain MPOBT, was isolated from a culture enriched from anaerobic granular sludge. It oxidized propionate syntrophically in co-culture with the hydrogen- and formate-utilizing Methanospirillum hungateii, and was able to oxidize propionate and other organic compounds in pure culture with sulfate or fumarate as the electron acceptor. Additionally, it fermented fumarate. 16S rRNA sequence analysis revealed a relationship with Syntrophobacter wolinii and Syntrophobacter pfennigii. The G + C content of its DNA was 60.6 mol%, which is in the same range as that of other Syntrophobacter species. DNA-DNA hybridization studies showed less than 26% hybridization among the different genomes of Syntrophobacter species and strain MPOBT. This justifies the assignment of strain MPOBT to the genus Syntrophobacter as a new species. The name Syntrophobacter fumaroxidans is proposed; strain MPOBT (= DSM 10017T) is the type strain.

Investigation of the fumarate metabolism of the syntrophic propionate-oxidizing bacterium strain MPOB

The growth of the syntrophic propionate-oxidizing bacterium strain MPOB in pure culture by fumarate disproportionation into carbon dioxide and succinate and by fumarate reduction with propionate, formate or hydrogen as electron donor was studied. The highest growth yield, 12.2 g dry cells/mol fumarate, was observed for growth by fumarate disproportionation. In the presence of hydrogen, formate or propionate, the growth yield was more than twice as low: 4.8, 4.6, and 5.2 g dry cells/mol fumarate, respectively. The location of enzymes that are involved in the electron transport chain during fumarate reduction in strain MPOB was analyzed. Fumarate reductase, succinate dehydrogenase, and ATPase were membrane-bound, while formate dehydrogenase and hydrogenase were loosely attached to the periplasmic side of the membrane. The cells contained cytochrome c, cytochrome b, menaquinone-6 and menaquinone-7 as possible electron carriers. Fumarate reduction with hydrogen in membranes of strain MPOB was inhibited by 2-(heptyl)-4-hydroxyquinoline-N-oxide (HOQNO). This inhibition, together with the activity of fumarate reductase with reduced 2,3-dimethyl-1,4-naphtoquinone (DMNH2) and the observation that cytochrome b of strain MPOB was oxidized by fumarate, suggested that menequinone and cytochrome b are involved in the electron transport during fumarate reduction in strain MPOB. The growth yields of fumarate reduction with hydrogen or formate as electron donor were similar to the growth yield of Wolinella succinogenes. Therefore, it can be assumed that strain MPOB gains the same amount of ATP from fumarate reduction as W. succinogenes, i. e. 0.7 mol ATP/mol fumarate. This value supports the hypothesis that syntrophic propionate-oxidizing bacteria have to invest two-thirds of an ATP via reversed electron transport in the succinate oxidation step during the oxidation of propionate. The same electron transport chain that is involved in fumarate reduction may operate in the reversed direction to drive the energetically unfavourable oxidation of succinate during syntrophic propionate oxidation since (1) cytochrome b was reduced by succinate and (2) succinate oxidation was similarly inhibited by HOQNO as fumarate reduction.

Caloramator proteoclasticus sp. nov., a new moderately thermophilic anaerobic proteolytic bacterium

A new moderately thermophilic proteolytic anaerobe, strain UT, was isolated from mesophilic granular methanogenic sludge. The cells were spore-forming, motile rods that were 0.4 micron wide and 2.4 to 4 microns long and stained gram negative. Electron micrographs of thin sections revealed the presence of an atypical gram-positive cell wall. Optimum growth occurred at 55 degrees C and at pH values between 7.0 and 7.5, with a doubling time of 30 min. The DNA base ratio of guanine plus cytosine was 31 mol%. The bacterium fermented proteins mainly to acetate, hydrogen, formate, and branched-chain fatty acids. Several amino acids, including glutamate, aspartate, arginine, histidine, threonine, methionine, and branched-chain amino acids, were also utilized. Glutamate was degraded to acetate, formate, hydrogen, and alanine. In addition, the strain degraded carbohydrates, including glucose, fructose, mannose, cellobiose, and starch, to acetate, ethanol, formate, lactate, and hydrogen. The results of a 16S rRNA sequence analysis phylogenetically placed strain UT in the low-guanine-plus-cytosine-content subgroup of the gram-positive phylum. We propose to classify the described strain in the genus Caloramator as a new species, Caloramator proteoclasticus. The type strain of C. proteoclasticus, strain U, has been deposited in the Deutsche Sammlung von Mikroorganismen as strain DSM 10124.

Understanding and advancing wastewater treatment

In bioreactors used for the purification of wastewater, microorganisms are active in biofilms or aggregates. Insight into the factors that determine the structure and function of aggregated biomass is increasing steadily. Besides conventional techniques, modem molecular techniques are used increasingly to get a better understanding of the complex microbial communities in wastewater treatment systems. In recent years, the combined use of these techniques has led to a good insight into the population dynamics of different types of microbes in bioreactors.

Taxonomic description of Methanococcoides euhalobius and its transfer to the Methanohalophilus genus

A sequence analysis of the 16S-rRNA of Methanococcoides euhalobius revealed that this organism was highly related to members of the genus Methanohalophilus. On the basis of sequence data, an oligonucleotide probe specific to Methanohalophilus species was designed. Hybridization studies with this probe confirmed close relationship of Methanococcoides euhalobius to Methanohalophilus species. Therefore, we propose that Methanococcoides euhalobius should be transferred to the genus Methanohalophilus as Methanohalophilus euhalobius.

Purification and characterization of malate dehydrogenase from the syntrophic propionate-oxidizing bacterium strain MPOB

Malate dehydrogenase from the syntrophic propionate-oxidizing bacterium strain MPOB was purified 42-fold. The native enzyme had an apparent molecular mass of 68 kDa and consisted of two subunits of 35 kDa. The enzyme exhibited maximum activity with oxaloacetate at pH 8.5 and 60 degrees C. The Ka for oxaloacetate was 50 microM and for NADH 30 microM. The Km values for L-malate and NAD were 4 and 1.1 mM, respectively. Substrate inhibition was found at oxaloacetate concentrations higher than 250 microM. The N-terminal amino acid sequence of the enzyme was similar to the sequences of a variety of other malate dehydrogenases from plants, animals and micro-organisms.

Population dynamics of propionate-oxidizing bacteria under methanogenic and sulfidogenic conditions in anaerobic granular sludge

Laboratory-scale upflow anaerobic sludge-bed reactors were inoculated with industrial granular sludge and fed with either propionate or propionate and sulfate. The population dynamics of the propionate-oxidizing bacteria Desulfobulbus sp. and the syntrophically growing strain SYN7 were studied in reactors by dot blot and in situ hybridization with 16S rRNA-based oligonucleotide probes.

Detection and localization of syntrophic propionate-oxidizing bacteria in granular sludge by in situ hybridization using 16S rRNA-based oligonucleotide probes

In situ hybridization with fluorescent oligonucleotides was used to detect and localize microorganisms in the granules of two lab-scale upflow anaerobic sludge blanket reactors that had been fed for several months with either sucrose or a mixture of volatile fatty acids. Sections of the granules were hybridized with 16S rRNA-targeted oligonucleotide probes for Bacteria, Archaea, specific phylogenetic groups of methanogens, and two syntrophic propionate-oxidizing strains, MPOB and KOPROP1. Cells of the syntrophic strain KOPROP1 were not detected in either type of sludge granules. Hybridizations of the sucrose-fed granules showed an outer layer of mainly bacterial microcolonies with different morphologies. More inwards of these granules, a layer of different methanogenic microcolonies mixed with large colonies of the syntrophic strain MPOB could be detected. The MPOB colonies were intertwined with hydrogen- or formate-consuming methanogens, indicating their syntrophic growth. The granules fed with volatile fatty acids showed an outer layer of mainly bacteria and then a thick layer of Methanosaeta-like methanogens mixed with a few bacteria and a layer of methanogens mixed with syntrophic MPOB microcolonies. The centers of both sludge types consisted of large cavities and methanogenic microcolonies. These results indicate a juxtapositioning of syntrophic bacteria and methanogens and provide additional evidence for a layered microbial architecture of anaerobic granular sludge.

Purification and characterization of fumarase from the syntrophic propionate-oxidizing bacterium strain MPOB

Fumarase from the syntrophic propionate-oxidizing bacterium strain MPOB was purified 130-fold under anoxic conditions. The native enzyme had an apparent molecular mass of 114 kDa and was composed of two subunits of 60 kDa. The enzyme exhibited maximum activity at pH 8.5 and approximately 54 degrees C. The Km values for fumarate and L-malate were 0.25 mM and 2.38 mM, respectively. Fumarase was inactivated by oxygen, but the activity could be restored by addition of Fe2+ and &beta;-mercaptoethanol under anoxic conditions. EPR spectroscopy of the purified enzyme revealed the presence of a [3Fe-4S] cluster. Under reducing conditions, only a trace amount of a [4Fe-4S] cluster was detected. Addition of fumarate resulted in a significant increase of this [4Fe-4S] signal. The N-terminal amino acid sequence showed similarity to the sequences of fumarase A and B of Escherichia coli (56%) and fumarase A of Salmonella typhimurium (63%).

Purification and characterization of a novel ADP-dependent glucokinase from the hyperthermophilic archaeon Pyrococcus furiosus

Pyrococcus furiosus uses a modified Embden-Meyerhof pathway during growth on poly- or disaccharides. Instead of the usual ATP-dependent glucokinase, this pathway involves a novel ADP-dependent (AMP-forming) glucokinase. The level of this enzyme and some other glycolytic enzymes appeared to be closely regulated by the substrate. Growth on cellobiose resulted in a high specific activity of 0.96 units mg-1, whereas on pyruvate a 10-fold lower activity was found. The ADP-dependent glucokinase was purified 1350-fold to homogeneity. The oxygen-stable enzyme had a molecular mass of 93 kDa and was composed of two identical subunits (47 kDa). The glucokinase was highly specific for ADP, which could not be replaced by ATP, phosphoenolpyruvate, GDP, PPi, or polyphosphate. D-Glucose could be replaced only by 2-deoxy-D-glucose, albeit with a low efficiency. The Km values for D-glucose and ADP were 0.73 and 0.033 mM, respectively. An optimum temperature of 105 degrees C and a half-life of 220 min at 100 degrees C are in agreement with the requirements of this hyperthermophilic organism. The properties of the glucokinase are compared to those of less thermoactive gluco/hexokinases.

Sulfate reduction by a syntrophic propionate-oxidizing bacterium

The syntrophic propionate-oxidizing bacterium MPOB was able to grow in the absence of methanogens by coupling the oxidation of propionate to the reduction of sulfate. Growth on propionate plus sulfate was very slow (mu = 0.024 day-1). An average growth yield was found of 1.5 g (dry weight) per mol of propionate. MPOB grew even slower than other sulfate-reducing syntrophic propionate-oxidizing bacteria. The growth rates and yields of strict sulfate-reducing bacteria (Desulfobulbus sp.) grown on propionate plus sulfate are considerably higher.

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 outcompetition 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.

Role of formate and hydrogen in the degradation of propionate and butyrate by defined suspended cocultures of acetogenic and methanogenic bacteria

The butyrate-degrading Syntrophospora bryantii degrades butyrate and a propionate-degrading strain (MPOB) degrades propionate in coculture with the hydrogen- and formate-utilizing Methanospirillum hungatii or Methanobacterium formicicum. However, the substrates are not degraded in constructed cocultures with two Methanobrevibacter arboriphilus strains which are only able to consume hydrogen. Pure cultures of the acetogenic bacteria form both hydrogen and formate during butyrate oxidation with pentenoate as electron acceptor and during propionate oxidation with fumarate as electron acceptor. Using the highest hydrogen and formate levels which can be reached by the acetogens and the lowest hydrogen and formate levels which can be maintained by the methanogens it appeared that the calculated formate diffusion rates are about 100 times higher than the calculated hydrogen diffusion rates.

Desulforhabdus amnigenus gen. nov. sp. nov., a sulfate reducer isolated from anaerobic granular sludge

From granular sludge of an upflow anaerobic sludge bed (UASB) reactor treating paper-mill wastewater, a sulfate-reducing bacterium (strain ASRB1) was isolated with acetate as sole carbon and energy source. The bacterium was rod-shaped, (1.4-1.9 x 2.5-3.4 microns), nonmotile, and gram-negative. Optimum growth with acetate occurred around 37 degrees C in freshwater medium (doubling time: 3.5-5.0 days). The bacterium grew on a range of organic acids, such as acetate, propionate, and butyrate, and on alcohols, and grew autotrophically with H2, CO2, and sulfate. Fastest growth occurred with formate, propionate, and ethanol (doubling time: approx. 1.5 days). Strain ASRB1 clusters with the delta subdivision of Proteobacteria and is closely related to Syntrophobacter wolinii, a syntrophic propionate oxidizer. Strain ASRB1 was characterized as a new genus and species: Desulforhabdus amnigenus.

Localization of the enzymes involved in H2 and formate metabolism in Syntrophospora bryantii

Cell-free extracts of crotonate-grown cells of the syntrophic butyrate-oxidizing bacterium Syntrophospora bryantii contained high hydrogenase activities (8.5-75.8 mumol.min-1mg-1 protein) and relatively low formate dehydrogenase activities (0.04-0.07 mumol.min-1 mg-1 protein). The KM value and threshold value of the hydrogenase for H2 were 0.21 mM and 18 microM, respectively, whereas the KM value and threshold value of the formate dehydrogenase for formate were 0.22 mM and 10 microM, respectively. Hydrogenase, butyryl-CoA dehydrogenase and 3-OH-butyryl-CoA dehydrogenase were detected in the cytoplasmic fraction. Formate dehydrogenase and CO2 reductase were membrane-bound, likely located at the outer aspect of the cytoplasmic membrane. Results suggest that during syntrophic butyrate oxidation H2 is formed intracellularly while formate is formed at the outside of the cell.

Enhanced biodegradation of aromatic pollutants in cocultures of anaerobic and aerobic bacterial consortia

Toxic aromatic pollutants, concentrated in industrial wastes and contaminated sites, can potentially be eliminated by low cost bioremediation systems. Most commonly, the goal of these treatment systems is directed at providing optimum environmental conditions for the mineralization of the pollutants by naturally occurring microflora. Electrophilic aromatic pollutants with multiple chloro, nitro and azo groups have proven to be persistent to biodegradation by aerobic bacteria. These compounds are readily reduced by anaerobic consortia to lower chlorinated aromatics or aromatic amines but are not mineralized further. The reduction increases the susceptibility of the aromatic molecule for oxygenolytic attack. Sequencing anaerobic and and aerobic biotreatment steps provide enhanced mineralization of many electrophilic aromatic pollutants. The combined activity of anaerobic and aerobic bacteria can also be obtained in a single treatment step if the bacteria are immobilized in particulate matrices (e.g. biofilm, soil aggregate, etc.). Due to the rapid uptake of oxygen by aerobes and facultative bacteria compared to the slow diffusion of oxygen, oxygen penetration into active biofilms seldom exceeds several hundred micrometers. The anaerobic microniches established inside the biofilms can be applied to the reduction of electron withdrawing functional groups in order to prepare recalcitrant aromatic compounds for further mineralization in the aerobic outer layer of the biofilm. Aside from mineralization, polyhydroxylated and chlorinated phenols as well as nitroaromatics and aromatic amines are susceptible to polymerization in aerobic environments. Consequently an alternative approach for bioremediation systems can be directed towards incorporating these aromatic pollutants into detoxified humic-like substances. The activation of aromatic pollutants for polymerization can potentially be encouraged by an anaerobic pretreatment step prior to oxidation. Anaerobic bacteria can modify aromatic pollutants by demethylating methoxy groups and reducing nitro groups. The resulting phenols and aromatic amines are readily polymerized in a subsequent aerobic step.