Continuous chemotrophic growth and respiration of Chromatiaceae species at low oxygen concentrations

Endogenous and maximum respiration rates of nine purple sulfur bacterial strains were determined. Endogenous rates were below 10 nmol O2 · (mg protein · min)-1 for sulfur-free cells and 15–35 nmol O2 · (mg protein · min)-1 for cells containg intracellular sulfur globules. With sulfide as electron-donating substrate respiration rates were considerably higher than with thiosulfate. Maximum respiration rates of Thiocystis violacea 2711 and Thiorhodovibrio winogradskyi SSP1 (254.8 and 264.2 nmol O2 · (mg protein · min)-1, respectively) are similar to those of aerobic bacteria. Biphasic respiration curves were obtained for sulfur-free cells of Thiocystis violacea 2711 and Chromatium vinosum 2811. In Thiocystis violacea the rapid and incomplete oxidation of thiosulfate was five times faster than the oxidation of stored sulfur. A high affinity of the respiratoty system for oxygen (K m =0.3–0.9 μM O2, V max=260 nmol O2 · (mg protein · min)-1 with sulfide as substrate, K m =0.6–2.4 μM O2, V max=14–40 nmol O2 · (mg protein · min)-1 with thiosulfate as substrate), for sulfide (K m =0.47 μM, V max=650 nmol H2S · (mg protein × min)-1, and for thiosulfate (K m =5–6 μM, V max =24–72 nmol S2O 3 2- · (mg protein · min)-1 was obtained for different strains. Respiration of Thiocystis violacea was inhibited by very low concentrations of NaCN (K i =1.7 μM) while CO concentrations of up to 300 μM were not inhibitory. The capacity for chemotrophic growth of six species was studied in continuous culture at oxygen concentrations of 11 to 67 μM. Thiocystis violacea 2711, Amoebobacter roseus 6611, Thiocapsa roseopersicina 6311 and Thiorhodovibrio winogradskyi SSP1 were able to grow chemotrophically with thiosulfate/acetate or sulfide/acetate. Chromatium vinosum 2811 and Amoebobacter purpureus ML1 failed to grow under these conditions. During shift from phototrophic to chemotrophic conditions intracellular sulfur and carbohydrate accumulated transiently inside the cells. During chemotrophic growth bacteriochlorophyll a was below the detection limit.