Lithoautotrophic growth of the freshwater strain Beggiatoa D-402 and energy conservation in a homogeneous culture under microoxic conditions

Abstract

The freshwater filamentous bacterium Beggiatoa D-402 was shown to grow lithoautotrophically in a homogeneous culture under microoxic conditions only, the growth yield being the highest at 0.1 mg O2 l−1. High activities of the Calvin cycle key enzymes and of the dissimilatory path thiosulfate oxidation enzymes were found in the bacterial cells. The rate of CO2 fixation above 112 nmol min−1 (mg protein)−1, an about 90% increase in the protein carbon at the expense of CO2 carbon and an increase in the molar yield up to 12 mg dry weight (mmol oxidized thiosulfate)−1 indicate the bacterial growth was autotrophic. Thiosulfate was oxidized by the strain almost completely into sulfate. The metabolically useful energy was conserved by oxidative phosphorylation that was coupled to oxidation of sulfur compounds. The bacterial membranes were found to contain CO-binding cytochromes b and two cytochromes c with Mr 23 and 26 kDa, the terminal part of the respiratory chain containing presumably a cbb3-type oxidase. A cytochrome c with Mr 12 kDa was detected in the soluble fraction.