CARBON METABOLISM OF BEGGIATOA LEPTOMITIFORMIS UNDER CONDITIONS OF CHEMOORGANOHETEROTROPHIC GROWTH

The activity of the enzymes of the tricarboxylic acid cycle (TCA cycle ) and of the glyoxylate cycle was determined in the filamentous colorl ess sulfur bacterium Beggiatoa leptomitiformis, strain D-405. The comp lete TCA cycle was demonstrated to function in the bacterium growing o n succinate, whereas the glyoxylate cycle functioned during growth on acetate or lactate. Aconitate hydratase activity in B. lepomitiformis was found to increase in the presence of Fe(II), which is tolerant to chemical oxidation in the reduced environment. The fumarate hydratase activity is inhibited by H2O2; therefore the presence of reducing agen ts is necessary to remove hydrogen peroxide produced and accumulated b y catalase-negative B. leptomitiformis. It is suggested that the lack of catalase in B. leptomitiformis and its dependence on reducing agent s is one of the causes which limit the habitats of the bacteria to hyd rogen sulfide ones.