Arsenite toxicity and arsenite tolerance in the cyanobacterium Synechococcus leopoliensis

Sodium arsenite at concentrations above 50 μM inhibited the growth of Synechococcus leopoliensis UTEX 625 in a defined culture medium. Inhibition was transitory, with growth resuming after a lag period the duration of which depended on the arsenite concentration. Cells grown for several hours in the presence of 10 μM arsenite became tolerant to concentrations of arsenite that inhibited the growth of untreated cells. Neither sensitive nor tolerant cells chemically modified the external arsenite detectably within the experimental period. At a concentration of 200 μM, arsenite temporarily halted growth of sensitive cells but did not affect that of tolerant cells. This concentration of arsenite inhibited net photosynthesis in both sensitive and tolerant cells. At the same time it selectively decreased the incorporation of carbon in the light into α-amino acids, especially glutamate, in sensitive but not in tolerant cells. Simultaneously, incorporation of carbon into pyruvic acid markedly increased. The activity of the partially purified pyruvate dehydrogenase complex of S. leopoliensis was abolished by 45 μM arsenite. It is concluded that inhibition of pyruvate dehydrogenase by arsenite is sufficient to explain its inhibition of growth in this organism.