SODIUM-DEPENDENT SUCCINATE DECARBOXYLATION BY A NEW ANAEROBIC BACTERIUM BELONGING TO THE GENUS PEPTOSTREPTOCOCCUS

An anaerobic bacterium was isolated from a polluted sediment, with suc cinate and yeast extract as carbon and energy sources. The new strain was Gram-positive, the cells were coccal shaped, the mol% G+C content of the genomic DNA was 29, and the peptidoglycan was of the L-ornithin e-D-glutamic acid type. Comparative sequence analysis of the 16S rRNA gene showed the new strain to belong to the genus Peptostreptococcus. Succinate, fumarate, pyruvate, 3-hydroxybutyrate and lysine supported growth. Succinate was degraded to propionate and presumably CO2, with a stoichiometric cell yield. Key enzymes of the methylmalonyl-CoA deca rboxylase pathway were present. The methylmalonyl-CoA decarboxylase ac tivity was avidin-sensitive and sodium dependent, and about 5 mM Na+ w as required for maximal activity. Whole cells, however, required at le ast 50 mM sodium for maximal succinate decarboxylation activity and to support the maximum growth rate. Sodium-dependent energy conservation coupled to succinate decarboxylation is shown for the first time to o ccur in a bacterium belonging to the group of Gram-positive bacteria c ontaining the peptostreptococci and their relatives.