In vitro metabolism of inorganic arsenic by the gastro-intestinal microflora of the rat.

The contents of the rat small intestine or caecum reduced sodium [74As] arsenate to arsenite over a period of 2-3 days. In the presence of caecal, but not small intestine, contents, small amounts of methyl arsonic acid and dimethylarsinic acid were formed. Stomach contents reduced arsenic very slowly. The metabolism of arsenate was inhibited by autoclaving the gut contents or by adding antibiotics, thus indicating that bacteria were involved. In prereduced media containing thioglycollate or cysteine in the absence of intestinal bacteria, sodium arsenate was reduced to arsenite. The rate of reduction of arsenate by the gut flora was increased by the presence of hydrogen sulphide or bile acids.