Oil-bioremediation potential of Arabian Gulf mud flats rich in diazotrophic hydrocarbon-utilizing bacteria

The numbers, identities and hydrocarbon-attenuation and nitrogen-fixation potential of bacteria in coastal slurry and microbial mat samples were investigated, using microscopic, culture-based and molecular approaches. Slurry and microbial mat samples were rich in picocyanobacteria, filamentous cyanobacteria and cultivable oil-utilizing bacteria which, according to their 16S rRNA gene sequences, were affiliated to Halomonas aquamarina, Marinobacter hydrocarbonoclasticus, Marinobacter sp; Dietzia maris and Alcanivorax sp. These isolates grew on crude oil and a wide range of individual aliphatic and aromatic hydrocarbons, as sole carbon and energy sources, and were diazotrophic. Slurry and mat samples were used directly as inocula for cleaning oily seawater in batch cultures. The combined potential of the slurry bacteria for hydrocarbon-utilization and nitrogen-fixation makes the consortia self-sufficient, as far as the nitrogen nutritional is concerned. The occurrence of oxygenic phototrophic microorganisms additionally makes such consortia self-sufficient in terms of oxygen requirements. It was concluded that coastal slurry has the potential for self-cleaning of oily coasts without need for nitrogen fertilization, and may be directly used as inocula for the bioremediation of oily liquid wastes.