Distribution of oil-degrading bacteria in coastal seawater, Toyama Bay, Japan.

Oil-degrading bacteria are considered to play an important role in the biodegradation of spilled or released oil in the sea. The distribution of indigenous oil-degrading bacteria in the coastal seawater of Toyama Bay, Japan, was examined. Surface seawater samples with or without oil film in fishing port were analyzed by denaturing gradient gel electrophoresis (DGGE) of the PCR-amplified V3 region of bacterial 16S rDNA. Sequence analysis revealed that several DGGE bands clearly detected only in samples with oil film corresponded to Cyanobacteria. Moreover, we cultured surface seawater samples with oil film in two different liquid culture media, a marine broth and an NSW medium; each culture contained 0.5% (w/v) C-heavy oil. Emulsification of the oil was observed at day 6 in the marine broth and day 9 in the NSW medium. Time-dependent changes of bacterial communities in those culture media were analyzed by DGGE. Interestingly, we found that Alcanivorax sp. became one of the dominant bacteria in each culture medium when emulsification of the oil began. Alcanivorax sp. is one of the well-known oil-degrading bacteria in seawater and is associated with the production of biosurfactants. These results suggest that Cyanobacteria and Alcanivorax play important roles in the bioremediation of oil-contaminated areas in Toyama Bay.