Abstract
The degradation processes of organoarsenic compounds in aquatic environments depend on microbial activities and significantly influence the arsenic cycles. In Lake Kahokugata, inorganic arsenic was detected through all seasons, while dimethylarsinic acid (DMAA) appeared at only winter seasons, and monomethylarsonic acid (MMAA) was not detected. The Most Probable Number (MPN) procedure detected the DMAA-degrading bacteria at cell densities ranging from 120 to 910 cells/ml. Moreover, when 1 μmol/l of DMAA was added to the water samples collected from Lake Kahokugata at every season, the 99% of DMAA was converted into inorganic arsenic within 35 days of incubation, suggesting that the biodegradation activities maintained same levels throughout all seasons. Total 352 isolates of DMAA-degrading bacteria seasonally obtained were classified into 10 types of which compositions seasonally varied, by the restriction-fragment-length polymorphism (RFLP) analysis of 16S rDNA. The representative 67 isolates degraded DMAA at the various degradation percentages of maximum 64% for 28 days. In particular, the dominated types at all seasons and winter seasons indicated high degradation activities, and phylogenetically belonged to the alpha-proteobacteria and the genus Pseudomonas, respectively. The seasonal similar activities of DMAA-degradation in Lake Kahokugata would depend on the several bacterial species of which compositions seasonally changes.
