Arsenic is a common trace element found in most natural waters, as well as a documented human carcinogen. In the environment, arsenic occurs in the valence states As(V) and As(III). The bioavailability of arsenic is in general controlled by the presence of iron, by sorption of arsenate (As(V)) to iron minerals, and sulfide, resulting in the precipitation of arsenite (As(III)) as arsenic sulfides. It is well known that arsenate may be microbiologically reduced under anaerobic conditions, and recently microbial reduction of arsenate coupled to the use of sulfide as electron donor was described [1, 2]. This process occurred in soda lakes, with pH 10 and high salt concentration, conditions under which sulfide is less toxic due to the virtual absence of H2S. Chemical reduction of arsenate with sulfide has been shown to take place at acidic to neutral pH. We investigated the possibility of biological reduction of arsenate with sulfide as electron donor at neutral pH. Batch incubations were set-up using anaerobic sediment amended with arsenate and sulfide. Arsenate was removed from solution in 5-9 days. In control experiments with autoclaved sediment, part of the arsenate in solution was removed, which may indicate relatively slow sorption of arsenate on soil particles or chemical reduction of arsenate. Incubations in which arsenate conversion occurred were transferred to fresh culture medium several times and yielded stable enrichment cultures. In these enrichment cultures two dominant bacterial species were present. Application of molecular biological techniques showed that the two species were related to the genus Sulfurospirillum and to sulfate reducing bacteria belonging to the delta-proteobacteria. We aim to isolate these two organisms in pure culture and study their physiology and ability to reduce arsenate with sulfide in more detail.
|Title of host publication||Geochimica et Cosmochimica Acta|
|Publication status||Published - 2007|