Bioremediation of oily sea water by bacteria immobilized in biofilms coating macroalgae

Using the standard plate method and a solid mineral medium containing crude oil as a sole source of carbon and energy, 10 different macroalgae from the Arabian Gulf were found associated with large numbers of oil-utilizing bacteria. Each gram fresh alga was associated with about two to about 30 million cells of bacteria predominantly belonging to the nocardioforms and the genus Acinetobacter. Shaking macroalgal samples in sea water batches containing known amounts of individual hydrocarbons led to considerable attenuation of these compounds as measured by GLC. Thus, bacteria associated with macroalgae consumed about 64–98% of n-octadecane and about 38–56% phenanthrene from medium aliquots containing 0.03% of the test hydrocarbon after 2 weeks. Meanwhile, the oil-utilizing bacteria, especially the nocardioforms, associated with the macroalgae increased in number by about 32–490 fold, depending on the macroalgae and hydrocarbons studied. On the other hand, relatively negligible numbers of bacteria were released into the sea water compared with the numbers immobilized on the macroalgal surfaces. Individual bacterial isolates could grow on a wide range of pure alkanes and aromatic hydrocarbons as sole sources of carbon and energy. It was concluded that macroalgae submerged in the sea waters are coated with biofilms rich in oil-utilizing bacteria, that contribute to hydrocarbon attenuation in water. These natural biological consortia represent valuable tools that could be of high potential for phytoremediation of oily sea water.