Inorganic Electron Acceptors Research Articles

Sporomusa malonica sp. nov., a homoacetogenic bacterium growing by decarboxylation of malonate or succinate

A new strictly anaerobic bacterium was isolated from an enrichment culture with glutarate as sole substrate and freshwater sediment as inoculum, however, glutarate was not metabolized by the pure culture. The isolate was a mesophilic, spore-forming, Gram-negative, motile curved rod. It fermented various organic acids, alcohols, fructose, acetoin, and H2/CO2 to acetate, usually as the only product. Other acids were fermented to acetate and propionate or acetate and butyrate. Succinate and malonate were decarboxylated to propionate or acetate, respectively, and served as sole sources of carbon and energy for growth. No inorganic electron acceptors except CO2 were reduced. Yeast extract (0.05% w/v) was required for growth. Small amounts of cytochrome b were detected in membrane fractions. The guanine-plus-cytosine content of the DNA was 44.1±2 mol%. The isolate is described as a new species of the genus Sporomusa, S. malonica.

Oxidation of glucose oxidase from Penicillium vitale by one- and two-electron acceptors

The steady-state oxidation of glucose oxidase Penicillium vitale by p-quinoids depends on the potential of electron acceptors; log k ox (M −1,s −1) = 3.2 + 8.4 E 7 0 (V) (pH 7.0, 25°C). Inorganic electron acceptors and organic compounds containing charged groups show a lower reactivity. The rate constant increase in the case of negatively charged acceptors proceeds parallel with the increase in the dissociation rate constant of FAD in the pH range 4–5. A lower reactivity of inorganic complexes and charged organic acceptors is related to the difficulties enountered by the ions penetrating to the enzyme active centre. The results obtained are interpreted in the framework of the outer spherical electron transfer theory. The distance of electron transfer calculated for the oxidation of glucose oxidase by inorganic complexes is equal to 11–13 Å at pH 7.0 and approx. 8 Å at pH 4.0.

Anaerobic metabolism of particulate organic matter in the sediments of a hypereutrophic lake*

SUMMARY. The anaerobic decomposition of particulate organic matter (POM) was examined in the anoxic pelagic sediments of hypereutrophic Wintergreen Lake. Degradation of sedimented POM occurred rapidly as shown by increased production and release of ammonia, hydrogen sulphide, volatile fatty acids and methane from the sediments 2–3 weeks after large inputs of organic matter. Maximum concentrations of most metabolites were found at the sediment‐water interface, indicating that the initial anaerobic degradation of freshly deposited POM occurred at this site. The absence of the inorganic electron acceptors, nitrate and sulphate, suggested that fermentation and methanogenesis were the major anaerobic processes involved in the dissimilation of organic matter in these sediments during stratified periods. The amount of carbon input converted to methane in the sediments was determined from May to early November 1976 and 1977. Carbon output as methane was measured by quantifying methane lost from the sediments by ebullition and by estimating soluble methane lost to the water column by diffusion. Total methane release during summer stratification accounted for 34% of the particulate organic carbon input to the sediments in 1976 and 44% in 1977. Methane release was directly related to the rate of sedimentation of POM. However, methane production was temporarily inhibited following high rates of sedimentation in 1976, suggesting that the rate of organic loading may be an important factor controlling anaerobic decomposition in these sediments.

Thiosulfate Oxidation and Tetrathionate Reduction by Intact Cells of Marine Pseudomonad Strain 16B

Levels of thiosulfate-oxidizing enzyme (TSO) and tetrathionate reductase (TTR) were measured in washed cell suspensions of a heterotrophic marine thiosulfate-oxidizing bacterium, strain 16B. TSO activity remained virtually constant in aerobically and anaerobically grown cells and was unaffected by the presence or absence of thiosulfate and tetrathionate in the growth medium. TTR was also present in cells grown aerobically and anaerobically, but its activity was threefold greater in cells cultured in media containing tetrathionate or thiosulfate. Tetrathionate appears to be the inducer of increased TTR activity in both aerobically and anaerobically grown cells. TTR (constitutive or induced) and TSO have different pH and temperature optima. Both TTR activities were unaffected by 10 mM KCN, which reversed oxygen inhibition of tetrathionate reduction. TSO was partially inhibited by 5 muM KCN and completely inhibited by 90 muM KCN. These findings and results of experiments to determine the influence of several inorganic electron donors and acceptors on TSO and TTR activities suggest that constitutive TSO and TTR represent reverse activities of the same enzyme, whereas inducible TTR is a separate enzyme used by strain 16B only for anaerobic respiration of tetrathionate. The bacterium appears well adapted to growth in environments characterized by low oxygen tension, dilute organic carbon concentrations, and the presence of a variety of reduced, inorganic sulfur compounds.

Influence of Nitrate on Fermentation Pattern, Molar Growth Yields and Synthesis of Cytochrome b in Propionibacterium pentosaceum

Under anaerobic conditions, Propionibacterium pentosaceum reduces nitrate to nitrite until nitrate is exhausted from the medium when nitrite is converted into N2 or N2O. In the presence of nitrate, fermentation patterns for lactate, glycerol and pyruvate were different from those obtained during anaerobic growth without an inorganic electron acceptor. In the presence of these substrates, a drastic decrease in propionate formation was observed, some pyruvate accumulated during growth with lactate, and acetate was produced from glycerol. Acetate production from lactate and pyruvate was not influenced by the presence of nitrate. Furthermore, CO2 was produced by citric acid cycle activity. The fermentation pattern during nitrite reduction resembled that of P. pentosaceum grown anaerobically without an inorganic electron acceptor. Nitrits has a toxic effect, since bacteria inoculated into a medium with 9 mM-nitrite failed to grow. The cytochrome spectrum of anaerobically grown P. pentosaceum was similar with and without nitrate. In membrane fractions of bacteria grown anaerobically with nitrate, cytochrome b functioned in the transfer of electrons from lactate, glycerol I-phosphate and NADH to nitrate. Molar growth yeilds were increased in the presence of nitrate, indicating an increased production of ATP. This could be explained by citric acid cycle activity, and by ocidative phosphorylation coupled to nitrate reduction. Assuming that I mol ATP is formed in the electron transfer from lactate or glycerol I-phosphate to nitrate, and that 2 mol ATP are formed in the electron transfer from NADH to nitrate, YATP values (g dry wt bacteria/mol ATP) were obtained of between 5-0 and 12-6. The higher YATP values were similar to those obtained during anaerobic growth without an inorganic electron acceptor. This supports the assumptions about the efficiency of oxidative phosphorylation for electron transport to nitrate. Low YAPT values were found when high concentrations of nitrite (15 to 50 mM) accumulated, and were probably due to the toxic effect of nitrite.

Electrical conductivity and spectral properties of polymer complexes based on 10-vinylphenothiazine and a halogen-containing inorganic electron acceptor

Electrical conductivity and spectral properties of polymer complexes based on 10-vinylphenothiazine and a halogen-containing inorganic electron acceptor