Degradation of arsenobetaine to inorganic arsenic by bacteria in seawater

The substances suspended in seawater were fractionated by membrane filtration into three fractions. Fraction 1 was collected on a membrane filter of 0.22 µm pore-size, fraction 2 on a 5 µm pore-size and fraction 3 on 0.22 µm pore-size from the filtrate passed through the 5 µm membrane filter. Arsenobetaine was incubated with each of these fractions in two media (ZoBell 2216E and a solution of inorganic salts) at 25 °C in the dark under aerobic conditions. The mixture added with fraction 3 was considered to contain only bacteria. In every case, in the inorganic salt medium, inorganic arsenic(V) was derived from arsenobetaine via trimethylarsine oxide. In the ZoBell medium, arsenobetaine was not degraded to inorganic arsenic, although trimethylarsine oxide was derived in every case. We conclude that the degradation of arsenobetaine to trimethylarsine oxide or inorganic arsenic can be accomplished in seawater by bacteria alone.