On the mechanism of autotrophic fixation of CO2 by Chloroflexus aurantiacus

The activity of two carboxylating enzymes was studied in the green filament ous bacterium Chloroflexus aurantiacus. The carboxylation reaction involvin g pyruvate synthase was optimized using (CO2)-C-14 and cell extracts. Pyruv ate synthase was shown to be absent from cells of Cfl. aurantiacus OK-70 an d present (in a quantity sufficient to account for autotrophic growth) in c ells of Cfl aurantiacus B-3. Differences in the levels of acetyl CoA carbox ylase activity were revealed between cells of the strains studied grown und er different conditions. The data obtained confirm the operation of differe nt mechanisms of autotrophic CO2 assimilation in Cfl aurantiacus B-3 and Cf l. aurantiacus OK-70: in the former organism, it is the reductive cycle of dicarboxylic acids, and in the latter one, it is the 3-hydroxypropionate cy cle.