BACTERIAL DISSIMILATORY REDUCTION OF ARSENIC(V) TO ARSENIC(III) IN ANOXIC SEDIMENTS

Incubation of anoxic salt marsh sediment slurries with 10 mM As(V) res ulted in the disappearance over time of the As(V) in conjunction with its recovery as As(III). No As(V) reduction to As(III) occurred in hea t-sterilized or formalin-killed controls or in live sediments incubate d in air, The rate of As(V) reduction in slurries was enhanced by addi tion of the electron donor lactate, H-2, or glucose, whereas the respi ratory inhibitor/uncoupler dinitrophenol, rotenone, or 2-heptyl-4-hydr oxyquinoline N-oxide blocked As(V) reduction, As(V) reduction was also inhibited by tungstate but not by molybdate, sulfate, or phosphate, N itrate inhibited As(V) reduction by its action as a preferred respirat ory electron acceptor rather than as a structural analog of As(V), Nit rate-respiring sediments could reduce As(V) to As(III) once all the ni trate was removed, Chloramphenicol blocked the reduction of As(V) to A s(III) in nitrate-respiring sediments, suggesting that nitrate and ars enate were reduced by separate enzyme systems, Oxidation of [2-C-14]ac etate to (CO2)-C-14 by salt marsh and freshwater sediments was coupled to As(V). Collectively, these results show that reduction of As(V) in sediments proceeds by a dissimilatory process, Bacterial sulfate redu ction was completely inhibited by As(V) as well as by As(III).