Cultures of Disulfovibrio desulfuricans strain CSN (incubated in a sulfide‐ and sulfate‐free medium) reduced up to 5 mM O2 with H2 as electron donor. Aerobic respiration was not coupled with growth, but resulted in ATP formation. Washed cells incubated in H2‐saturated phosphate buffer revealed respiration rates of up to 250 nmol O2 min−1 mg protein−1. The uncoupler carbonyl‐cyanide m‐chlorophenylhydrazone (CCCP) stimulated the respiration rate and abolished ATP formation. The terminal oxidase has not yet been identified. Respiration was microaerophilic, insensitive to cyanide and azide, but inhibited after heat treatment of the cells (80°C for 10 min). The ph optimum was at pH 6 with less than 50% activity at pH 4.5 and pH 9. Besides H2, organic eletron donors (formate, ethanol, lactate or pyruvate) and inorganic sulfur compounds (H2S, thiosulfate, sulfite) were used as electron donors for aerobic respiration. Sulfite and thiosulfate were oxidized completely to sulfate. The capability of aerobic respiration was also detected in Desulfovibrio vulgaris, D. sulfidismutans, Desulfobacterium autotrophim, Desulfobulbus propionicus, and Desulfococcus multivorans.
Methylammonium was taken up rapidly by illuminated cells of Anacystis nidulans R-2, leading to internal concentrations of 1.3 0.1 mM within 1 min, and a gradient of up to 200 between the cells and medium. Accumulation of 14CH3NH3' required at least 5 mM NaCl, but the uptake rate was independent of medium pH between 6.5 and 9. The kinetics of uptake could be resolved into an initial fast phase lasting less than 1 min (approximate Ki,, 7.2 ,uM; Vmax, 12.5 nmol minmg of protein-l at 15°C). A second, slower phase associated with product formation was eliminated by preincubation with methionine sulfoximine, a specific inhibitor of glutamine synthetase; the rapid phase was unaffected by this treatment. Ammonium ions competed with 4CH3NH3' for entry, and addition of 5 ,iM NH4' or 100 ,uM CH3NH3+ released 14CH3NH3+ accumulated during the rapid phase of entry. Small additions of NH4+ made at the same time as additions of 14CH3NH3+ delayed the start of radioactivity uptake by a time which corresponded accurately with the period needed for the complete removal of the added NH4+. The effects of inhibitors on accumulation and carbocyanine dye fluorescence suggest that ATP-dependent membrane potential was needed to drive 14CH3NH3+ transport. Spheroplasts were as active as whole cells in accumulating NH4' and 14CH3NH3', indicating that soluble
A rod-shaped, motile, phototrophic bacterium, strain SiCys, was enriched and isolated from a marine microbial mat, with cysteine as sole substrate. During phototrophic anaerobic growth with cysteine, sulfide was produced as an intermediate, which was subsequently oxidized to sulfate. The molar growth yield with cysteine was 103 g mol-1, in accordance with complete assimilation of electrons from the carbon and the sulfur moiety into cell material. Growth yields with alanine and serine were proportionally lower. Thiosulfate, sulfide, hydrogen, and several organic compounds were used as electron donors in the light, whereas cystine, sulfite, or elemental sulfur did not support phototrophic anaerobic growth. Aerobic growth in the dark was possible with fructose as substrate. Cultures of strain SiCys were yellowish-brown in color and contained bacteriochlorophyll a, spheroidene, spheroidenone, and OH-spheroidene as major photosynthetic pigments. Taking the morphology, photosynthetic pigments, aerobic growth in the dark, and utilization of sulfide for phototrophic growth into account, strain SiCys was assigned to the genus Rhodovulum (formerly Rhodobacter) and tentatively classified as a strain of R. sulfidophilum. In cell-free extracts in the presence of pyridoxal phosphate, cysteine was converted to pyruvate and sulfide, which is characteristic for cysteine desulfhydrase activity (l-cystathionine gamma-lyase, EC 4.4. 1.1).
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