Molecular detection of marine bacterial populations on beaches contaminated by the Nakhodka tanker oil-spill accident

In January 1997, the tanker Nakhodka sank in the Japan Sea, and more than 5 000 tons of heavy oil leaked. The released oil contaminated more than 500 k m of the coastline, and some still remained even by June 1999, To investiga te the long-term influence of the Nakhodka oil spill on marine bacterial po pulations, sea water and residual oil were sampled from the oil-contaminate d zones 10, 18, 22 and 29 months after the accident, and the bacterial popu lations in these samples were analysed by denaturing gradient gel electroph oresis (DGGE) of PCR-amplified 16S rDNA fragments. The dominant DGGE bands were sequenced, and the sequences were compared with those in DNA sequence libraries. Most of the bacteria in the sea water samples were classified as the Cytophaga-Flavobacterium-Bacteroides phylum, a-Proteobacteria or cyano bacteria, The bacteria detected in the oil paste samples were different fro m those detected in the sea water samples; they were types related to hydro carbon degraders, exemplified by strains closely related to Sphingomonas su barctica and Alcanivorax borkumensis, The sizes of the major bacterial popu lations in the oil paste samples ranged from 3.4 x 10(5) to 1.6 x 10(6) bac teria per gram of oil paste, these low numbers explaining the slow rate of natural attenuation.