[metabolism of the phase variants of the phototrophic bacterium Rhodobacter sphaeroides]

Growth, bacteriochlorophyll a content, electron transport chain (ETC), and activities of the tricarboxylic acid (TCA) cycle enzymes were studied in R and M phase variants of Rhodobactersphaeroides cells grown anaerobically in the light and aerobically in the dark. Under all cultivation conditions tested, bacteriochlorophyll a content was 2-3 times lower in the cells of the M. variant compared to the R variant, which therefore was predominant in the cultures grown in the light. In both variants, activity of all TCA cycle enzymes was higher for the cells grown in the dark under aerobic conditions. When grown aerobically in the dark, the R variant, unlike the M variant, did not contain cytochrome aa3, acting as. cytochrome c oxidase, in its ETC. An additional point of coupling the electron transfer to the generation of the proton gradient al the cytochrome aa3 level provided for more efficient oxidation of organic substrates, resulting in predominance of the M variant in the cultures grown in the dark under aerobic conditions.