Conversion of arsenobetaine to dimethylarsinic acid by arsenobetaine‐decomposing bacteria isolated from coastal sediment

Abstract Arsenobetain [(CH 3 ) 3 As + CH 2 COO ‐ ]‐containing growth media (1/5 ZoBell 2216E and solution of inorganic salts) were inoculated with two bacterial strains, which were isolated from a coastal sediment and identified as members of the Vibro‐Aeromonas group, and incubated under aerobic and anaerobic conditions. Arsenobetaine was converted to a metabolite only under aerobic conditions. This arsenic metabolite was identified as dimethylarsinic acid [(CH 3 ) 2 AsOOH] by hydride generation/cold trap/GC MS/SIM analysis and high‐performance liquid‐chromatographic behaviour. The conversion pattern shown by these arsenobetaine‐decomposing bacteria (that is, arsenobetaine → dimethylarsinic acid) was fairly different from that shown by the addition of sediment itself as the source of arsenobetaine‐decomposing micro‐organisms (that is, arsenobetaine → trimethylarsine oxide → inorganic arsenic). This result suggests to us that various micro‐organisms, including the arsenobetaine‐decomposing bacteria isolated in this study, participate in the degradation of arsenobetaine in marine environments.