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.     

Isomerization between n-butyrate and isobutyrate in enrichment cultures

Abstract An isobutyrate-degrading methanogenic enrichment was obtained from a mesophilic anaerobic digester. Studies with growing cells and cell suspensions showed a reversible isomerization between butyrate and isobutyrate, suggesting that butyrate is an intermediate in the anaerobic degradation of isobutyrate. NMR experiments with ¹³C-labelled butyrate demonstrated that this isomerization resulted from the migration of the carboxyl group.     

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.     

Reciprocal Isomerization of Butyrate and Isobutyrate by the Strictly Anaerobic Bacterium Strain WoG13 and Methanogenic Isobutyrate Degradation by a Defined Triculture

Isomerization of butyrate and isobutyrate was investigated with the recently isolated strictly anaerobic bacterium strain WoG13 which ferments glutarate to butyrate, isobutyrate, CO₂, and small amounts of acetate. Dense cell suspensions converted butyrate to isobutyrate and isobutyrate to butyrate. ¹³C-nuclear magnetic resonance experiments proved that this isomerization was accomplished by migration of the carboxyl group to the adjacent carbon atom. In cell extracts, both butyrate and isobutyrate were activated to their coenzyme A (CoA) esters by acyl-CoA:acetate CoA-transferases. The reciprocal rearrangement of butyryl-CoA and isobutyryl-CoA was catalyzed by a butyryl-CoA:isobutyryl-CoA mutase which depended strictly on the presence of coenzyme B₁₂. Isobutyrate was completely degraded via butyrate to acetate and methane by a defined triculture of strain WoG13, Syntrophomonas wolfei, and Methanospirillum hungatei.     

Resistance of Streptomyces cinnamonensis to butyrate and isobutyrate: production and properties of a new anti-isobutyrate (AIB) factor.

Butyrate and isobutyrate (after isomerization to n-butyrate) are specific precursors for the biosynthesis of monensin A in Streptomyces cinnamonensis. High concentrations of both butyrate and isobutyrate (greater than 20 and 10 mM, respectively) were toxic to S. cinnamonensis plated on solid medium. Spontaneous mutants resistant to these substances were isolated. These new strains produced monensins at even higher concentrations of butyrate or isobutyrate, with an increased yield of monensin A. S. cinnamonensis produced an anti-isobutyrate (AIB) factor, which was originally found to be excreted by some isobutyrate-resistant stains growing on solid medium containing isobutyrate. On plates, the AIB factor efficiently counteracted toxic concentrations not only of isobutyrate, but also of acetate, propionate, butyrate, 2-methylbutyrate, valerate and isovalerate against S. cinnamonensis as well as other Streptomyces species. Although the AIB factor enabled normal growth, sporulation and monensin production on plates, it did not have positive effects on submerged cultures of S. cinnamonensis with isobutyrate. The partial purification of the AIB factor was achieved. The role of the AIB factor during spore germination on solid medium containing isobutyrate or its homologues is discussed.     

Insertional Inactivation of Methylmalonyl Coenzyme A (CoA) Mutase and Isobutyryl-CoA Mutase Genes in Streptomyces cinnamonensis: Influence on Polyketide Antibiotic Biosynthesis

The coenzyme B(12)-dependent isobutyryl coenzyme A (CoA) mutase (ICM) and methylmalonyl-CoA mutase (MCM) catalyze the isomerization of n-butyryl-CoA to isobutyryl-CoA and of methylmalonyl-CoA to succinyl-CoA, respectively. The influence that both mutases have on the conversion of n- and isobutyryl-CoA to methylmalonyl-CoA and the use of the latter in polyketide biosynthesis have been investigated with the polyether antibiotic (monensin) producer Streptomyces cinnamonensis. Mutants prepared by inserting a hygromycin resistance gene (hygB) into either icmA or mutB, encoding the large subunits of ICM and MCM, respectively, have been characterized. The icmA::hygB mutant was unable to grow on valine or isobutyrate as the sole carbon source but grew normally on butyrate, indicating a key role for ICM in valine and isobutyrate metabolism in minimal medium. The mutB::hygB mutant was unable to grow on propionate and grew only weakly on butyrate and isobutyrate as sole carbon sources. (13)C-labeling experiments show that in both mutants butyrate and acetoacetate may be incorporated into the propionate units in monensin A without cleavage to acetate units. Hence, n-butyryl-CoA may be converted into methylmalonyl-CoA through a carbon skeleton rearrangement for which neither ICM nor MCM alone is essential.     

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     

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

Two strains of new strictly anaerobic, gramnegative 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 bedemonstrated 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.     

Effect of precursors on biosynthesis of monensins A and B

Precursors of monensins (acetate, propionate, butyrate, isobutyrate) affect the total production and the relative proportion of monensins A and B. Addition of propionate into the fermentation medium causes a prevalence of monensin B whereas butyrate and isobutyrate stimulate the production of monensin A and suppress the production of monensin B.     

Coenzyme A transferase from Clostridium acetobutylicum ATCC 824 and its role in the uptake of acids.

Coenzyme A (CoA) transferase from Clostridium acetobutylicum ATCC 824 was purified 81-fold to homogeneity. This enzyme was stable in the presence of 0.5 M ammonium sulfate and 20% (vol/vol) glycerol, whereas activity was rapidly lost in the absence of these stabilizers. The kinetic binding mechanism was Ping Pong Bi Bi, and the Km values at pH 7.5 and 30 degrees C for acetate, propionate, and butyrate were, respectively, 1,200, 1,000, and 660 mM, while the Km value for acetoacetyl-CoA ranged from about 7 to 56 microM, depending on the acid substrate. The Km values for butyrate and acetate were high relative to the intracellular concentrations of these species; consequently, in vivo enzyme activity is expected to be sensitive to changes in those concentrations. In addition to the carboxylic acids listed above, this CoA transferase was able to convert valerate, isobutyrate, and crotonate; however, the conversion of formate, n-caproate, and isovalerate was not detected. The acetate and butyrate conversion reactions in vitro were inhibited by physiological levels of acetone and butanol, and this may be another factor in the in vivo regulation of enzyme activity. The optimum pH of acetate conversion was broad, with at least 80% of maximal activity from pH 5.9 to greater than 7.8. The purified enzyme was a heterotetramer with subunit molecular weights of about 23,000 and 25,000.     

Coenzyme A transferase from Clostridium acetobutylicum ATCC 824 and its role in the uptake of acids

Coenzyme A (CoA) transferase from Clostridium acetobutylicum ATCC 824 was purified 81-fold to homogeneity. This enzyme was stable in the presence of 0.5 M ammonium sulfate and 20% (vol/vol) glycerol, whereas activity was rapidly lost in the absence of these stabilizers. The kinetic binding mechanism was Ping Pong Bi Bi, and the Km values at pH 7.5 and 30 degrees C for acetate, propionate, and butyrate were, respectively, 1,200, 1,000, and 660 mM, while the Km value for acetoacetyl-CoA ranged from about 7 to 56 microM, depending on the acid substrate. The Km values for butyrate and acetate were high relative to the intracellular concentrations of these species; consequently, in vivo enzyme activity is expected to be sensitive to changes in those concentrations. In addition to the carboxylic acids listed above, this CoA transferase was able to convert valerate, isobutyrate, and crotonate; however, the conversion of formate, n-caproate, and isovalerate was not detected. The acetate and butyrate conversion reactions in vitro were inhibited by physiological levels of acetone and butanol, and this may be another factor in the in vivo regulation of enzyme activity. The optimum pH of acetate conversion was broad, with at least 80% of maximal activity from pH 5.9 to greater than 7.8. The purified enzyme was a heterotetramer with subunit molecular weights of about 23,000 and 25,000.     

Isobutyrate as a precursor of n-butyrate in the biosynthesis of tylosine and fatty acids

Labelled sodium isobutyrate [(CD3)2-CHCOONa] was added to the culture medium of Streptomyces fradiae and up to 14 atoms of deuterium were found to be incorporated into a molecule of tylosin aglycone (tylactone). This observation is in accordance with the data in the literature. When fatty acids were analyzed, as much as 34% of the isobutyrate incorporated into the cell was formed to be transformed into butyrate that was used for the synthesis of even, straight-chain fatty acids; 57% of the labelled isobutyrate was incorporated into the even isoacids, whereas 9% was degraded to propionate and further used for the synthesis of the odd acids.     

Role of short-chain fatty acids in colonic HCO(3) secretion

Luminal isobutyrate, a relatively poor metabolized short-chain fatty acid (SCFA), induces HCO(3) secretion via a Cl-independent, DIDS-insensitive, carrier-mediated process as well as inhibiting both Cl-dependent and cAMP-induced HCO(3) secretion. The mechanism(s) responsible for these processes have not been well characterized. HCO(3) secretion was measured in isolated colonic mucosa mounted in Lucite chambers using pH stat technique and during microperfusion of isolated colonic crypts. (14)C-labeled butyrate, (14)C-labeled isobutyrate, and (36)Cl uptake were also determined by apical membrane vesicles (AMV) isolated from surface and/or crypt cells. Butyrate stimulation of Cl-independent, DIDS-insensitive 5-nitro-3-(3-phenylpropyl-amino)benzoic acid-insensitive HCO(3) secretion is greater than that by isobutyrate, suggesting that both SCFA transport and metabolism are critical for HCO(3) secretion. Both lumen and serosal 25 mM butyrate inhibit cAMP-induced HCO(3) secretion to a comparable degree (98 vs. 90%). In contrast, Cl-dependent HCO(3) secretion is downregulated by lumen 25 mM butyrate considerably more than by serosal butyrate (98 vs. 37%). Butyrate did not induce HCO(3) secretion in isolated microperfused crypts, whereas an outward-directed HCO(3) gradient-driven induced (14)C-butyrate uptake by surface but not crypt cell AMV. Both (36)Cl/HCO(3) exchange and potential-dependent (36)Cl movement in AMV were inhibited by 96-98% by 20 mM butyrate. We conclude that 1) SCFA-dependent HCO(3) secretion is the result of SCFA transport across the apical membrane via a SCFA/HCO(3) exchange more than intracellular SCFA metabolism; 2) SCFA-dependent HCO(3) secretion is most likely a result of an apical membrane SCFA/HCO(3) exchange in surface epithelial cells; 3) SCFA downregulates Cl-dependent and cAMP-induced HCO(3) secretion secondary to SCFA inhibition of apical membrane Cl/HCO(3) exchange and anion channel activity, respectively.     

Development of a method for heterologous gene expression in Enterobacter amnigenus, a potential host for the biological control of mosquito larvi

An integrative plasmid containing a 1.3 kb fragment of chromosomal DNA from Enterobacter amnigenus was constructed. The Omega fragment encoding spectinomycin/streptomycin resistance was cloned into the unique BglII site of the resulting plasmid, and the interrupted fragment was transferred via plasmid pMAK705 by electroporation into E. amnigenus with a selection for spectinomycin resistance. Cointegrants were resolved to generate an E. amnigenus strain that expressed spectinomycin resistance, but grew as rapidly as the parental strain. The cloned fragment encodes a putative homologue of the proW gene of Escherichia coli that is not essential for E. amnigenus growth. The integrative plasmid is now available to introduce any heterologous DNA into the E. amnigenus chromosome, for the construction of promoter-probe vectors for the studies of gene regulation, or to construct plasmids suitable for the isolation of secretion signals. Immediate applications of this system will include the expression and secretion of crystal toxins from bacilli for the biological control of mosquito larvae infected with the bacterial host.     

Kinetic mechanism and identification of the active site tyrosine residue in Enterobacter amnigenus arylsulfate sulfotransferase.

Bacterial arylsulfate sulfotransferase (ASST) catalyzes the transfer of a sulfate group from a phenyl sulfate ester to a phenolic acceptor. The kinetic mechanism of Enterobacter amnigenus ASST was determined. Plots of 1/v versus 1/[substrate (A)] at different fixed substrate (B) concentrations gave a series of parallel lines. One of the reaction products, p-nitrophenol, inhibited the enzyme noncompetitively with respect to p-nitrophenyl sulfate, but competitively to alpha-naphthol. These results correspond to a ping pong bi bi mechanism. By site-directed mutagenesis, we substituted each conserved tyrosine residue with phenylalanine. Among the mutants, Y123F showed severely reduced catalytic activity. We conclude that Tyr 123 is an essential active site residue. A mechanistic hypothesis is presented to account for these observations.     

Activity of the AIB factor observed in prokaryotic and eukaryotic microorganisms

Streptomyces cinnamonensis produces a new substance named AIB (for anti-isobutyrate) factor which, on a solid medium, efficiently counteracts toxic concentrations not only of isobutyrate but also of other salts of short-chain monocarboxylic acids. In the present study we demonstrate that the AIB factor activity is widely spread because this effect was positively detected in 25 of 31 randomly chosen microorganisms (streptomycetes, ascomycetes, zygomycetes and basidiomycetes). The AIB factor produced by the tested microorganisms on an agar media allows for germination, growth, and sporulation of the testingStreptomyces coelicolor on an agar medium containing 20 mmol/L acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, and 2-methylbutyrate. The activity of the AIB factor from different sources towards these substances differs.     

Transmembrane hyperpolarization and increase of K+ uptake in maize roots treated with permeant weak acids

Abstract. Treatment with weak acids (butyrate, isobutyrate, trimethylacetate, DMO) at a concentration of I mol m⁻³ in apical maize root segments induced a rapid, marked hyperpolarization ( ca. 30 mV) of the transmembrane electrical potential, stable for at least 30 min. With butyrate, this effect increased with the increase of butyrate concentration in the medium, reaching a value of ca. 75 mV at a concentration of 5 mol m⁻³.
Both the butyrate uptake and the hyperpolarization were roughly proportional to the pH-regulated, undissociated/dissociated acid ratio in the medium. The butyrate-induced hyperpolarization was reduced progressively, but was still present when K⁺ concentration in the medium was raised from 1 to 10 mol m⁻³.
The hyperpolarization was accompanied by a significant increase of K⁺ uptake, and was almost completely suppressed by the presence of the protonophore carbonylcyanid- p -trichlorometoxy-phenylhydrazone (CCCP) and strongly reduced by erytrosin B, an inhibitor of some animal ATPases and of a K⁺-activated, DCCD- and vanadate-sensitive Mg²⁺-ATPase from plant microsomes. The hyperpolarization effect of butyrate was additive to that of fusicoccin at low, but not at high (5 mol m⁻³), concentrations of the weak acid. These results suggest that the intracellular pH regulates the activity of the electrogenic proton pump at the plasmalemma.     

Induction of cholera toxin receptors in cultured cells by butyric acid.

Exposure of HeLa cells to sodium butyrate caused an increase in choleragen (cholera toxin) receptors as measured by increased binding of 125I-choleragen to the intact cells. The process was dependent on time and butyrate concentration; maximal increases (over 40-fold) were observed at 48 h and 5 mM sodium butyrate. Other short chain fatty acids were less effective in elevating choleragen receptors in the order: butyrate greater than pentanoate greater than hexanoate greater than propionate. Acetate and isobutyrate had no effect. The increase in toxin receptors caused by butyrate was reversible and occurred in serum-free medium. The affinity of choleragen for control and butyrate-treated HeLa cells appeared to be similar. Butyrate also induced an elevation in choleragen receptors in rat C6 glial and Friend erythroleukemic cells but not in a butyrate-resistant HeLa mutant. The increase observed in Friend cells paralleled the increase in ganglioside GM1 (galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide), the reported choleragen receptor. Although no GM1 could be detected in untreated Hela cells, small amounts were found in cells exposed to butyrate.     

Detection and quantification of Desulforhabdus amnigenus in anaerobic granular sludge by dot blot hybridization and PCR amplification

A species-specific 16S rRNA oligonucleotide probe (ASRB1) was developed for the detection of Desulforhabdus amnigenus in anaerobic granular sludge. The presence of nucleic acids from cells of D. amnigenus in granular sludge was determined using ASRB1 as a specific primer for polymerase chain reaction (PCR) amplification or as a probe for dot blot hybridizations. The detection threshold and the reproducibility of these two methods were determined with sludge amended with 10⁴–10¹⁰ D. amnigenus cells per gram of volatile suspended solids (VSS). For D. amnigenus cells with a ribosomal RNA content of 15 fg cell⁻¹, the lowest number of target cells detected by hybridization was 1 × 10⁸ cells g⁻¹ VSS. With the PCR amplification method the lowest number of target cells which could be detected was 1 × 10⁷ g⁻¹ VSS. This corresponds to a threshold level for hybridization of 0·1–0·001‰ of the total bacterial sludge population, while the threshold level obtained with the PCR approach amounted to 0·01–0·0001‰. The rRNA content of D. amnigenus was found to be affected by the growth rate and the growth phase, and it ranged from 19 fg cell⁻¹ in slow-growing cultures to 90 fg cell⁻¹ in fast-growing cultures. Therefore, the detection threshold of the dot blot hybridization method for fast-growing cells is lower than for slow-growing cells.