Comparison of oil degrading microbial communities in sediments from the Persian Gulf and Caspian Sea

The responses of the natural microbial community in contaminated and uncontaminated sediments of the Persian Gulf and the Caspian Sea were evaluated by microcosm experiments. Analysis of bacterial densities (total heterotrophic, hydrocarbon-degrading and hydrocarbonoclastic bacteria count), microbial metabolic activities (enzymatic activities), and detection of catabolic genes of alkane hydroxylase systems by PCR were performed on subsurface sediment during 120 days of the experiment. The results showed that contaminated sediments from both areas had high dehydrogenase and lipase activities and low alpha-glucosidase activity. Lipase and dehydrogenase activities in Persian Gulf sediments were more than from Caspian Sea sediments. On the other hand, Caspian Sea sediments have lower dehydrogenase and lipase activity than the Persian Gulf. PCR analysis revealed the presence of alkane hydroxylase genes in both sediments with prevalence in contaminated sediments. Moreover, by PCR analysis with specific primers, the alkB(1) gene of Alcanivorax sp. was detected only in contaminated seawater from the Persian Gulf as well as in artificially oil-contaminated seawater from the Persian Gulf and Caspian Sea. Apparently, the exposure to petroleum hydrocarbons contamination altered the microbial and enzymatic activities of sediments. The detection of alkB1 gene has been suggested as an indicator of oil contamination.