Biodegradation of Polycyclic Aromatic Hydr ocarbons (PAHs) by Bacterial S pecies Isolated from Oily Polluted S oils

Twenty five bacterial isolates were isolated from three types of oily polluted soils which were Al - Najaf Oil Refinery/Najaf and two fuel stations in Hilla which were Ishtar and Al - Hilla Al - Jadida. These isolates were purified and identif ied according to phenotypic and microscopic properties in addition to biochemical tests. The results showed that these isolate belonging to five different bacterial species, three of them are gram negative bacteria which were: Pseudomonas aeruginosa , Pseud omonas putida and Acinetobacter baumannii , while two of them were gram positive bacteria which were Staphylococcus epidermidis and Bacillus sp. Preliminary experiment was done to show the ability of these isolates to grow on hydrocarbons mixture (1%) as a s ole source of carbon and energy, by denotation of viable bacterial count (CFU/ml) for seven days of incubation period. T he results explained that the gram - negative bacterial isolates have such ability, while the gram - positive bacterial isolates didn't have this ability. Three parameters were used to evaluate the biodegradation efficiency of the isolates hydrocarbons consumption percentage, reduction of surface tension and production of biosurfactant. The most efficient isolate was P. putida which consumed 7 8, 76.6 and 55.5% of phenanthrene, anthracene and pyrene, respectively, at 37 ˚c, pH=7 with agitation. Also it reduced the surface tension of the medium to 44.1 dyns/cm when it consumed phenanthrene and 53.2 dyns/cm for anthracene and 55.2 dyns/cm for pyren e compared with 72.2 dyns/cm of control sample. In the same conditions it produced biosurfactant at concentration of 40, 37.1 and 31.1 mg/L for phenanthrene, anthracene and pyrene, respectively, while P. aeruginosa consumed 70, 66.5 and 50.1% at the same c ondition from phenanthrene, anthracene and pyrene, respectively, also it reduced the surface tension of the medium to 46.9, 54.5 and 57.2 dyns/cm and it produced biosurfactant at concentration of 34.5, 32.5 and 28.2 mg/L when it consumed phenanthrene, anth racene and pyrene, respectively. On the other hand A. baumannii consumed 56% from phenanthrene, 54.1% from anthracene and 43.2% from pyrene and it reduced the surface tension of the medium to 49.3, 55.3 and 61.3 dyns/cm for phenanthrene, anthracene and pyr ene, respectively, while it produced biosurfactant at concentration of 30.1, 29.2 and 22.3 mg/L when it consumed phenanthrene, anthracene and pyrene, respectively. Consortium of three efficient isolates ( P. putida, P. aeruginosa and A. baumannii ) was made. The results explained that the consortium efficiency increased more than the individual isolates when consumed 100, 95 and 88% of phenanthrene, anthracene and pyrene, respectively, at the seventh day of incubation. Keywords : Biodegradation/PAHs/Consortium / Pseudomonas / Acinetobacter .