Oil-consuming microbial consortia floating in the Arabian Gulf

Picocyanobacteria floating on the surface of the water body in the Arabian Gulf were found associated with heterotrophic bacteria. Haemocytometer counting of fresh 1-cm surface water revealed 10 7 –10 8 bacterial cells ml −1 , but only 10 2 –10 3 cells ml −1 in 10-cm deep water samples. The heterotrophic bacteria comprised hydrocarbon utilizers that could grow on a mineral medium containing crude oil as sole carbon and energy source. Three-week liquid cultures of the picocyanobacteria Synechococcus , Synechocystis , Pleurocapsa and Dermocarpella were found by dilution plating to contain 10 6 –10 13 oil-utilizing bacteria ml −1 . These were members of the genera Pseudomonas , Bacillus and Acinetobacter and nocardioforms. Growth and hydrocarbon consumption potential of individual types of oil-utilizing bacteria in culture were higher in the presence of the picocyanobacteria than in their absence. Evidence was presented that picocyanobacterial cells may accumulate hydrocarbons from the medium, and subsequently make those compounds available to the associated hydrocarbon-utilizing bacteria. It was concluded that this microbial consortium, which is apparently of cosmopolitan occurrence, could be active in controlling marine oil-pollution.