Attenuation of oil pollutants in the Arabian Gulf water by bacteria naturally associated with live fish

This paper describes the potential of oil-utilizing bacteria associated with live fish from the Arabian Gulf for hydrocarbon attenuation in seawater polluted with oil. Maintaining local live fish (grey mullet and tilapia) in seawater artificially polluted with crude oil or individual hydrocarbons for 3 w led to dramatic attenuation of those compounds. The same result was obtained when instead of live fish, the bacterial consortia scraped off from the fish surfaces were used. Almost similar hydrocarbon attenuation results were obtained irrespective of whether the system was fertilized with NH4NO3 or not. Parallel counting of oil-utilizing bacteria associated with fish on a nitrogen-containing and a nitrogen free-medium gave almost similar numbers, indicating that most of the hydrocarbon-utilizing bacteria could fix atmospheric nitrogen. The predominant hydrocarbon-utilizing bacteria isolated from fish grew well in nitrogen-free medium and gave positive nitrogenase test as revealed by their potential for acetylene reduction to ethylene. Molecular fingerprinting showed that crude oil-polluted seawater samples incubated for 3 w contained two new 16S rDNA bands probably corresponding to hydrocarbon-utilizing bacteria. It was concluded that fish individuals accommodate rich bacterial consortia with the combined potential for hydrocarbon-utilization and nitrogen-fixation, which makes them efficient in cleaning hydrocarbon pollutants in water without need for nitrogen fertilization.