Selenium-dependent growth of Treponema denticola:: evidence for a clostridial-type glycine reductase

Assessment of the nutritional requirements of Treponema denticola disclosed a strict growth dependence on selenium. In vivo labeling of cells of this organism with Se-75 and electrophoretic analysis revealed three labeled bands, two of which were selenoproteins correlating in size with subunits A and B of glycine reductase. Antibodies directed against glycine- or betaine-reductase subunits of Eubacterium acidaminophilum specifically also reacted with proteins from cell lysates of T denticola. Moreover, ORFs within the T denticola genome sequence were found whose products display high sequence similarity to glycine-reductase subunits. These findings strongly support the notion that T denticola ferments amino acids via the activity of glycine reductase, an enzyme previously thought to be restricted to gram-positive bacteria.