Complete assimilation of cysteine by a newly isolated non-sulfur purple bacterium resembling Rhodovulum sulfidophilum (Rhodobacter sulfidophilus).

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).

Methylammonium transport in Anacystis nidulans R-2.

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 Km, 7.2 microM; Vmax, 12.5 nmol min-1 mg of protein-1 at 15 degrees 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 14CH3NH3+ for entry, and addition of 5 microM NH4+ or 100 microM 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 periplasmic components are not involved in the translocation. Some significant differences between the translocation of 14CH3NH3 and that of NH4+ were observed: growth with NH4+ in place of NO3- repressed 14CH3NH3+ accumulation ability without affecting the NH4+ uptake rate Na+ was not required for NH4+ uptake, and concentration of KCl inhibitory with 14C3NH3+ did not reduce NH4+ uptake.