PECULIARITIES OF CARBON METABOLISM IN THE FILAMENTOUS SULFUR BACTERIATHIOTHRIX-ARCTOPHILA AND LEUCOTHRIX-THIOPHILA DURING CHEMOLITHOHETEROTROPHIC AND CHEMOORGANOHETEROTROPHIC GROWTH

The tricarboxylic acid (TCA) and glyoxylate cycles were found to funct ion concurrently in the filamentous sulfur bacteria Thiothrix arctophi la and Leucothrix thiophila. During heterotrophic growth, the activity of the dehydrogenases of the TCA cycle in these bacteria was an order of magnitude lower than in other heterotrophic bacteria. During litho heterotrophic growth with thiosulfate, the activity of the TCA cycle h ydratases (aconitate hydratase, fumarate hydratase, and isocitrate lya se) and dehydrogenases (isocitrate dehydrogenase, succinate dehydrogen ase, and malate dehydrogenase) decreased 10- to 30-fold and two- to th ree-fold, respectively; the activity of the glyoxylate cycle enzymes, which supply the ''building material'' for constructive metabolism, di d not change. Thus, thiosulfate oxidation was accompanied by a shift i n the flow of reducing agents (NADH and NADPH) from the TCA cycle to t he glyoxylate cycle, providing a 20-30% increase in the biomass yield.