Enzymes Involved in Anaerobic Polyethylene Glycol Degradation by Pelobacter venetianus and Bacteroides Strain PG1

In extracts of polyethylene glycol (PEG)-grown cells of the strictly anaerobically fermenting bacterium Pelobacter venetianus , two different enzyme activities were detected, a diol dehydratase and a PEG-degrading enzyme which was characterized as a PEG acetaldehyde lyase. Both enzymes were oxygen sensitive and depended on a reductant, such as titanium citrate or sulfhydryl compounds, for optimal activity. The diol dehydratase was inhibited by various corrinoids (adenosylcobalamin, cyanocobalamin, hydroxocobalamin, and methylcobalamin) by up to 37% at a concentration of 100 μM. Changes in ionic strength and the K + ion concentration had only limited effects on this enzyme activity; glycerol inhibited the enzyme by 95%. The PEG-degrading enzyme activity was stimulated by the same corrinoids by up to 80%, exhibited optimal activity in 0.75 M potassium phosphate buffer or in the presence of 4 M KCI, and was only slightly affected by glycerol. Both enzymes were located in the cytoplasmic space. Also, another PEG-degrading bacterium, Bacteroides strain PG1, contained a PEG acetaldehyde lyase activity analogous to the corresponding enzyme of P. venetianus but no diol dehydratase. Our results confirm that corrinoid-influenced PEG degradation analogous to a diol dehydratase reaction is a common strategy among several different strictly anaerobic PEG-degrading bacteria.

Fermentative degradation of dipicolinic acid (pyridine-2,6-dicarboxylic acid) by a defined coculture of strictly anaerobic bacteria

Degradation of dipicolinic acid (pyridine-2,6-dicarboxylic acid) under strictly anaerobic conditions was studied in enrichment cultures from marine and freshwater sediments. In all cases, dipicolinic acid was completely degraded. From an enrichment culture from a marine sediment, a defined coculture of two bacteria was isolated. The dipicolinic acid-fermenting bacterium was a Gram-negative, non-sporeforming strictly anaerobic short rod which utilized dipicolinic acid as sole source of carbon, energy, and nitrogen, and fermented it to acetate, propionate, ammonia, and 2CO2. No other substrate was fermented. This bacterium could be cultivated only in coculture with another Gram-negative, non-sporeforming rod from the same enrichment culture which oxidized acetate to CO2 with fumarate, malate, or elemental sulfur as electron acceptor, similar to Desulfuromonas acetoxidans. Since this metabolic activity is not important in substrate degradation by the coculture, the basis of the dependence of the dipicolinic acid-degrading bacterium on the sulfur reducer may be sought in the assimilatory metabolism.

A strictly anaerobic nitrate-reducing bacterium growing with resorcinol and other aromatic compounds

With resorcinol as sole source of energy and organic carbon, two stains of gram-negative, nitrate-reducing bacteria were isolated under strictly anaerobic conditions. Strain LuBRes1 was facultatively anaerobic and catalase- and superoxide dismutase-positive. This strain was affiliated with Alcaligenes denitrificans on the basis of substrate utilization spectrum and peritrichous flagellation. Strain LuFRes1 could grow only under anaerobic conditions with oxidized nitrogen compounds as electron acceptor. Cells were catalase-negative but superoxide dismutase-positive. Since this strain was apparently an obligate nitrate reducer, it could not be grouped with any existing genus. Resorcinol was completely oxidized to CO2 by both strains. Neither an enzyme activity reducing or hydrolyzing the resorcinol molecule, nor an acyl-CoA-synthetase activating resorcylic acids or benzoate was detected in cell-free extracts of cells grown with resorcinol. In dense cell suspensions, both strains produced a compound which was identified as 5-oxo-2-hexenoic acid by mass spectrometric analysis. This would indicate a direct, hydrolytic cleavage of the resorcinol nucleus without initial reduction.

Sequential Transhydroxylations Converting Hydroxyhydroquinone to Phloroglucinol in the Strictly Anaerobic, Fermentative Bacterium Pelobacter massiliensis

The recently isolated fermenting bacterium Pelobacter massiliensis is the only strict anaerobe known to grow on hydroxyhydroquinone (1,2,4-trihydroxybenzene) as the sole source of carbon and energy, converting it to stoichiometric amounts of acetate. In this paper, we report on the enzymatic reactions involved in the conversion of hydroxyhydroquinone and pyrogallol (1,2,3-trihydroxybenzene) to phloroglucinol (1,3,5-trihydroxybenzene). Cell extracts of P. massiliensis transhydroxylate pyrogallol to phloroglucinol after addition of 1,2,3,5-tetrahydroxybenzene (1,2,3,5-TTHB) as cosubstrate in a reaction identical to that found earlier with Pelobacter acidigallici (A. Brune and B. Schink, J. Bacteriol. 172:1070-1076, 1990). Hydroxyhydroquinone conversion to phloroglucinol is initiated in cell extracts without an external addition of cosubstrates. It involves a minimum of three consecutive transhydroxylation reactions characterized by the transient accumulation of two different TTHB isomers. Chemical synthesis of the TTHB intermediates allowed the resolution of the distinct transhydroxylation steps in this sequence. In an initial transhydroxylation, the hydroxyl group in the 1-position of a molecule of hydroxyhydroquinone is transferred to the 5-position of another molecule of hydroxyhydroquinone to give 1,2,4,5-TTHB and resorcinol (1,3-dihydroxybenzene) as products. Following this disproportionation of hydroxyhydroquinone, the 1,2,4,5-isomer is converted to 1,2,3,5-TTHB, an enzymatic activity present only in hydroxyhydroquinone-grown cells. Finally, phloroglucinol is formed from 1,2,3,5-TTHB by transfer of the 2-hydroxyl group to either hydroxyhydroquinone or resorcinol. The resulting coproducts are again cosubstrates in earlier reactions of this sequence. From the spectrum of hydroxybenzenes transhydroxylated by the cell extracts, the minimum structural prerequisites that render a hydroxybenzene a hydroxyl donor or acceptor are deduced.

Energy conservation in malolactic fermentation by Lactobacillus plantarum and Lactobacillus sake

A comparably poor growth medium containing 0.1% yeast extract as sole non-defined constituent was developed which allowed good reproducible growth of lactic acid bacteria. Of seven different strains of lactic acid bacteria tested, only Lactobacillus plantarum and Lactobacillus sake were found to catalyze stoichiometric conversion of L-malate to L-lactate and CO2 concomitant with growth. The specific growth yield of malate fermentation to lactate at pH 5.0 was 2.0 g and 3.7 g per mol with L. plantarum and L. sake, respectively. Growth in batch cultures depended linearly on the malate concentration provided. Malate was decarboxylated nearly exclusively by the cytoplasmically localized malo-lactic enzyme. No other C4-dicarboxylic acid-decarboxylating enzyme activity could be detected at significant activity in cell-free extracts. In pH-controlled continuous cultures, L. plantarum grew well with glucose as substrate, but not with malate. Addition of lactate to continuous cultures metabolizing glucose or malate decreased cell yields significantly. These results indicate that malo-lactic fermentation by these bacteria can be coupled with energy conservation, and that membrane energetization and ATP synthesis through this metabolic activity are due to malate uptake and/or lactate excretion rather than to an ion-translocating decarboxylase enzyme.

Energy conservation by succinate decarboxylation in Veillonella parvula

Veillonella parvula cannot grow with succinate as sole energy source. However, succinate decarboxylation simultaneous with malate or lactate fermentation increased growth yields by 2.4-3.5 g (mol succinate)-1. Malate was fermented stoichiometrically to acetate and propionate whereas lactate fermentation produced more acetate and considerable amounts of H2. Aspartate was utilized only in the presence of succinate as co-substrate. Methylmalonyl-CoA decarboxylase and ATP-dependent pyruvate carboxylase, but not methylmalonyl-CoA:pyruvate transcarboxylase, were detected in cell-free extracts of malate- or lactate-grown cells. The energetic aspects of these fermentation patterns are discussed.

Fermentative degradation of glutarate via decarboxylation by newly isolated strictly anaerobic bacteria

Two strains of new strictly anaerobic, gram-negative bacteria were enriched and isolated from a freshwater (strain WoG13) and a saltwater (strain CuG11) anoxic sediment with glutarate as sole energy source. Strain WoG13 formed spores whereas strain CuG11 did not. Both strains were rod-shaped, motile bacteria growing in carbonate-buffered, sulfide-reduced mineral medium supplemented with 2% of rumen fluid. Both strains fermented glutarate to butyrate, isobutyrate, CO2, and small amounts of acetate. With methylsuccinate, the same products were formed, and succinate was fermented to propionate and CO2. No sugars, amino acids or other organic acids were used as substrates. Molar growth yields (Ys) were very small (0.5-0.9 g cell dry mass/mol dicarboxylate). Cells of strain WoG13 contained no cytochromes, and the DNA base ratio was 49.0 +/- 1.4 mol% guanine-plus-cytosine. Enzyme activities involved in glutarate degradation could be demonstrated in cell-free extracts of strain WoG13. A pathway of glutarate fermentation via decarboxylation of glutaconyl-CoA to crotonyl-CoA is suggested which forms butyrate and partly isobutyrate by subsequent isomerization.

Anaerobic degradation of 3-hydroxybenzoate by a newly isolated nitrate-reducing bacterium

A Gram-negative nitrate-reducing bacterium, strain Asl-3, was isolated from activated sludge with nitrate and 3-hydroxybenzoate as sole source of carbon and energy. The new isolate was facultatively anaerobic, catalase- and oxidase-positive and polarly monotrichously flagellated. In addition to nitrate, nitrite, N2O, and O2 served as electron acceptors. Growth with 3-hydroxybenzoate and nitrate was biphasic: nitrate was completely reduced to nitrite before nitrite reduction to N2 started. Benzoate, 3-hydroxybenzoate, 4-hydroxybenzoate, protocatechuate or phenyl-acetate served as electron and carbon source under aerobic and anaerobic conditions. During growth with excess carbon source, poly-beta-hydroxybutyrate was formed. These characteristics allow the affiliation of strain Asl-3 with the family Pseudomonadaceae. Analogous to the pathway of 4-hydroxybenzoate degradation in other bacteria, the initial step in anaerobic 3-hydroxybenzoate degradation by this organism was activation to 3-hydroxy-benzoyl-CoA in an ATP-consuming reaction. Cell extracts of 3-hydroxybenzoate-grown cells exhibited 3-hydroxybenzoyl-CoA synthetase activity of 190 nmol min-1 mg protein-1 as well as benzoyl-CoA synthetase activity of 86 nmol min-1 mg protein-1. A reductive dehydroxylation of 3-hydroxybenzoyl-CoA could not be demonstrated due to rapid hydrolysis of chemically synthesized 3-hydroxybenzoyl-CoA by cell extracts.

Lithotrophic growth and hydrogen metabolism by Clostridium magnum

Clostridium magnum, originally described as a non-autotrophic homoacetogenic bacterium, was found to be able to grow with H2/CO2, formate, or methanol with stoichiometric acetate formation, provided that the growth medium contained at least 0.025% (w/v) yeast extract. Hydrogen was also formed as a byproduct of glucose fermentation, and was consumed again after glucose consumption. Hydrogen formation from glucose was independent of growth conditions and reached similar maximal concentrations in mineral media with or without ammonia added as well as in non-growing cultures or in the presence of carbon monoxide.

Identification of two porins in Pelobacter venetianus fermenting high-molecular-mass polyethylene glycols

Porins were purified from cells of the anaerobic gram-negative bacterium Pelobacter venetianus grown with 20-kDa polyethylene glycol. After treatment of the cell envelope fraction with sodium dodecyl sulfate-containing solutions, the murein contained only two major peptidoglycan-associated proteins of 14 and 23 kDa. Both proteins were released from the peptidoglycan by the detergent Triton X-100. Genapol X-80 released only the 23-kDa protein. This protein was purified by chromatography on a hydroxyapatite column. It did not form sodium dodecyl sulfate-resistant oligomers. Reconstituted in lipid bilayer membranes, the 23-kDa protein formed cation-selective channels with a single-channel conductance of 230 pS in 1 M KCl. The channel is not a general-diffusion pore, since its conductance depends only moderately on the salt concentration. The channel conducted ammonium much better than potassium or rubidium ions, suggesting that it is probably involved in ammonium uptake. The outer membrane of P. venetianus contains a further, non-murein-associated pore with an unknown molecular mass. It is also cationically selective and has a single-channel conductance of 1.6 nS in 1 M KCl, which suggests that its effective diameter is similar to that of porins from enteric bacteria.

Anaerobic degradation of sorbic acid by sulfate-reducing and fermenting bacteria: pentanone-2 and isopentanone-2 as byproducts

Strictly anaerobic bacteria were enriched and isolated from freshwater sediment sources in the presence and absence of sulfate with sorbic acid as sole source of carbon and energy. Strain WoSo1, a Gram-negative vibrioid sulfate-reducing bacterium which was assigned to the species Desulfoarculus (formerly Desulfovibrio) baarsii oxidized sorbic acid completely to CO2 with concomitant stoichiometric reduction of sulfate to sulfide. This strain also oxidized a wide variety of fatty acids and other organic compounds. A Gram-negative rod-shaped fermenting bacterium, strain AmSo1, fermented sorbic acid stoichiometrically to about equal amounts of acetate and butyrate. At concentrations higher than 10 mM, sorbic acid fermentation led to the production of pentanone-2 and isopentanone-2 (3-methyl-2-butanone) as byproducts. Strain AmSo1 fermented also crotonate and 3-hydroxybutyrate to acetate and butyrate, and hexoses to acetate, ethanol, hydrogen, and formate. The guanine-plus-cytosine content of the DNA was 41.8 +/- 1.0 mol%. Sorbic acid at concentrations higher than 5 mM inhibited growth of this strain while strain WoSo1 tolerated sorbic acid up to 10 mM concentration.

Ether-cleaving enzyme and diol dehydratase involved in anaerobic polyethylene glycol degradation by a new Acetobacterium sp

A strictly anaerobic, homoacetogenic bacterium was enriched and isolated from anoxic sewage sludge with polyethylene glycol (PEG) 1000 as sole source of carbon and energy, and was assigned to the genus Acetobacterium on the basis of morphological and physiological properties. The new isolate fermented ethylene glycol and PEG's with molecular masses of 106 to 1000 to acetate and small amounts of ethanol. The PEG-degrading activity was not destroyed by proteinase K treatment of whole cells. In cell-free extracts, a diol dehydratase and a PEG-degrading (ether-cleaving) enzyme activity were detected which both formed acetaldehyde as reaction product. The diol dehydratase enzyme was oxygen-sensitive and was stimulated 10-14 fold by added adenosylcobalamine. This enzyme was found mainly in the cytoplasmic fraction (65%) and to some extent (35%) in the membrane fraction. The ether-cleaving enzyme activity reacted with PEG's of molecular masses of 106 to more than 20000. The enzyme was measurable optimally in buffers of high ionic strength (4.0), was extremely oxygen-sensitive, and was inhibited by various corrinoids (adenosylcobalamine, cyanocobalamine, hydroxocobalamine, methylcobalamine). This enzyme was found exclusively in the cytoplasmic fraction. It is concluded that PEG is degraded by this bacterium inside the cytoplasm by a hydroxyl shift reaction, analogous to a diol dehydratase reaction, to form an unstable hemiacetal intermediate. The name polyethylene glycol acetaldehyde lyase is suggested for the responsible enzyme.

Anaerobic degradation of acetone by Desulfococcus biacutus spec. nov

From anaerobic digestor sludge of a waste water treatment plant, a gram-negative, strictly anaerobic sulfate-reducing bacterium was isolated with acetone as sole organic substrate. The bacterium was characterized as a new species, Desulfococcus biacutus. The strain grew with acetone with doubling times of 72 h to 120 h; the growth yield was 12.0 (+/- 2.1) g x [mol acetone]-1. Acetone was oxidized completely, and no isopropanol was formed. In labelling studies with 14CO2, cell lipids (including approx. 50% PHB) of acetone-grown cells became labelled 7 times as high as those of 3-hydroxy-butyrate-grown cells. Enzyme studies indicated that acetone was degraded via acetoacetyl-CoA, and that acetone was channeled into the intermediary metabolism after condensation with carbon dioxide to a C4-compound, possibly free acetoacetate. Acetoacetyl-CoA is cleaved by a thiolase reaction to acetyl-CoA which is completely oxidized through the carbon monoxide dehydrogenase pathway. Strain KMRActS was deposited with the Deutsche Sammlung von Mikroorganismen, Braunschweig, under the number DSM 5651.

Clostridium homopropionicum sp. nov., a new strict anaerobe growing with 2-, 3-, or 4-hydroxybutyrate

From anoxic sewage sludge a new strictly anaerobic, spore-forming bacterium was isolated with 2-hydroxybutyrate as sole substrate. 2-, 3-, and 4-hydroxybutyrate, 4-chlorobutyrate, crotonate, vinylacetate, and pyruvate were fermented to acetate and butyrate. Fructose was converted to acetate, butyrate, butanol, and H2. Lactate and acrylate were fermented to acetate and propionate. Cells pregrown with lactate fermented 2-hydroxybutyrate to butyrate, propionate and acetate. No inorganic electron acceptors were reduced. The DNA base ratio was 32.0 +/- 1.0 mol% and was similar to that of Clostridium propionicum, which was determined to be 35.3 +/- 0.5 mol%. Strain LuHBu1 is described as type strain of a new species, Clostridium homopropionicum sp. nov. Another isolate obtained from marine sediment degraded 2- and 3-hydroxybutyrate to acetate and butyrate and was in some respects similar to the known species Ilyobacter polytropus.

Anaerobic degradation of 1,3-propanediol by sulfate-reducing and by fermenting bacteria

Three strains of strictly anaerobic Gram-negative, non-sporeforming, motile bacteria were enriched and isolated from freshwater sediments with 1,3-propanediol as sole energy and carbon source. Strain OttPdl was a sulfate-reducing bacterium which grew also with lactate, ethanol, propanol, butanol, 1,4-butanediol, formate or hydrogen plus CO2, the latter only in the presence of acetate. In the absence of sulfate, most of these substrates were fermented to the respective fatty acids in syntrophic cooperation with Methanospirillum hungatei. Sulfur, thiosulfate, or sulfite were reduced, nitrate not. The other two isolates degraded propanediol only in coculture with Methanospirillum hungatei. Strain OttGlycl grew in pure culture with acetoin and with glycerol in the presence of acetate. Strain WoAcl grew in pure culture only with acetoin. Both strains did not grow with other substrates, and did not reduce nitrate, sulfate, sulfur, thiosulfate or sulfite. The isolates were affiliated with the genera Desulfovibrio and Pelobacter. The pathways of propanediol degradation and the ecological importance of this process are discussed.

Pyrogallol-to-phloroglucinol conversion and other hydroxyl-transfer reactions catalyzed by cell extracts of Pelobacter acidigallici

Permeabilized cells and cell extracts of Pelobacter acidigallici catalyzed the conversion of pyrogallol (1,2,3-trihydroxybenzene) to phloroglucinol (1,3,5-trihydroxybenzene) in the presence of 1,2,3,5-tetrahydroxybenzene. Pyrogallol consumption by resting cells stopped after lysis by French press or mild detergent (cetyltrimethylammonium bromide [CTAB]) treatment. Addition of 1,2,3,5-tetrahydroxybenzene to the assay mixture restored pyrogallol consumption and led to stoichiometric phloroglucinol accumulation. The stoichiometry of pyrogallol conversion to phloroglucinol was independent of the amount of tetrahydroxybenzene added. The tetrahydroxybenzene concentration limited the velocity of the transhydroxylation reaction, which reached a maximum at 1.5 mM tetrahydroxybenzene (1 U/mg of protein). Transhydroxylation was shown to be reversible. The equilibrium constant of the reaction was determined, and the free-energy change (delta G degree') of phloroglucinol formation from pyrogallol was calculated to be -15.5 kJ/mol. Permeabilized cells and cell extracts also catalyzed the transfer of hydroxyl moieties between other hydroxylated benzenes. Tetrahydroxybenzene and hydroxyhydroquinone participated as hydroxyl donors and as hydroxyl acceptors in the reaction, whereas pyrogallol, resorcinol, and phloroglucinol were hydroxylated by both donors. A novel mechanism deduced from these data involves intermolecular transfer of the hydroxyl moiety from the cosubstrate (1,2,3,5-tetrahydroxybenzene) to the substrate (pyrogallol), thus forming the product (phloroglucinol) and regenerating the cosubstrate.

Anaerobic degradation of acetone and higher ketones via carboxylation by newly isolated denitrifying bacteria

Five strains of Gram-negative denitrifying bacteria that used various ketones as sole carbon and energy sources were isolated from activated sludge from a municipal sewage plant. Three strains are related to the genus Pseudomonas; two non-motile species have not yet been affiliated. All strains grew well with ketones and fatty acids (C2 to C7), but sugars were seldom utilized. The physiology of anaerobic acetone degradation was studied with strain BunN, which was originally enriched with butanone. Bicarbonate was essential for growth with acetone under anaerobic and aerobic conditions, but not if acetate or 3-hydroxybutyrate were used as substrates. An apparent Ks value of 5.6 mM-bicarbonate was determined for growth with acetone in batch culture. The molar growth yield was 24.8-29.8 g dry cell matter (mol acetone consumed)-1, with nitrate as the electron acceptor in batch culture; it varied slightly with the extent of poly-beta-hydroxybutyric acid (PHB) formation. During growth with acetone, 14CO2 was incorporated mainly into the C-1 atom of the monomers of the storage polymer PHB. With 3-hydroxybutyrate as substrate, 14CO2 incorporation into PHB was negligible. The results provide evidence that acetone is channelled into the intermediary metabolism of this strain via carboxylation to acetoacetate.

Fermentative degradation of nonionic surfactants and polyethylene glycol by enrichment cultures and by pure cultures of homoacetogenic and propionate-forming bacteria

Linear alkyl ethoxylates (polyethylene glycol alkyl ethers) were fermented completely to methane and CO2 in enrichment cultures inoculated with anoxic sewage sludge. Long-chain fatty acids were released as intermediates. No degradation was found with polypropylene glycol and polypropylene glycol-containing surfactants. Two types of primary ethoxylate-degrading bacteria were isolated and characterized. Both degraded polyethylene glycols with molecular weights of 1,000 completely. Strain KoB35 fermented polyethylene glycol, ethoxyethanol, and lactate to acetate and propionate and was assigned to the described species Pelobacter propionicus. Strain KoB58 converted polyethylene glycol and many other substrates to acetate only and was assigned to the genus Acetobacterium. The pathways of anaerobic degradation of nonionic surfactants are discussed with respect to their limitations and the various groups of bacteria involved.

Methanogenic degradation of acetone by an enrichment culture

An anaerobic enrichment culture degraded 1 mol of acetone to 2 mol of methane and 1 mol of carbon dioxide. Two microorganisms were involved in this process, a filament-forming rod similar to Methanothrix sp. and an unknown rod with round to slightly pointed ends. Both organisms formed aggregates up to 300 micron in diameter. No fluorescing bacteria were observed indicating that hydrogen or formate-utilizing methanogens are not involved in this process. Acetate was utilized in this culture by the Methanothrix sp. Inhibition of methanogenesis by bromoethanesulfonic acid or acetylene decreased the acetone degradation rate drastically and led to the formation of 2 mol acetate per mol of acetone. Streptomycin completely inhibited acetone degradation, and neither acetate nor methane was formed. 14CO2 was incorporated exclusively into the C-1 atom of acetate indicating that acetone is degraded via carboxylation to an acetoacetate residue. It is concluded that acetone is degraded by a coculture of an eubacterium and an acetate-utilizing methanogen and that acetate is the only intermediate transferred between both. The energetical problems of the eubacterium converting acetone to acetate are discussed.