PHYSIOLOGY OF SELENITE REDUCTION BY ENTEROCOCCI: I. INFLUENCE OF ENVIRONMENTAL VARIABLES

Environmental factors affecting the reduction of selenite by growing and resting cells of Streptococcus faecalis N83 and Streptococcus faecium K6A, respectively, were studied. Both organisms displayed an intrinsic capacity to reduce selenite to the metallic selenium in a complex medium. However, concentrations of selenite above 50 μg/ml proved toxic to S. faecium, while S. faecalis tolerated and reduced selenite at concentrations as high as 1000 μg/ml. The pH optimum for selenite reduction lay between 7.2 and 7.7 for both organisms. Though maximum selenite reduction was shown by both under anaerobic conditions, S. faecalis, but not S. faecium, reduced selenite substantially even under aeration. The reduction of selenite by S. faecalis did not appear to be directly conditioned by the oxidation-reduction potential of the medium; a low potential was, however, necessary for the reduction of selenite by S. faecium. The presence of a flavin compound was associated with maximum reduction of selenite by S. faecalis, but effected no change in selenite reduction by S. faecium. The growth of these organisms could not be coupled to the reduction of selenite.