Desu Dibe ulfuri enzot B izatio thiop Bacte on an hene erial I nd Ut e by S Isola tiliza Some ates ation e Loc of cal

The main aim of this study was obtaining efficient bacteria capable of desulfurizing and/or utilizing organosulfur compounds that found in petroleum and its derivatives. For this purpose oil contaminated soil samples with a history of oil pollution were collected from forty different sites in Iraq.Sixty three bacterial isolates were obtained and these isolates capable to utilize dibenzothiophene (DBT). Results showed that most of these isolates were capable to grow on DBT in the presence or without glycerol (carbon source). The growth density of bacterial isolates in presence of glycerol was more than growth density without glycerol. Results also showed that the growth density of bacterial isolates was a little more in medium containing ethanol plus magnesium sulfate compared to the growth in DBT plus ethanol medium. This means that these isolates were capable to utilize ethanol as C- source.  From all isolates, only three isolates (M9, M19 and S25) had the ability to desulfurize DBT (cleave C-S bond) and converted it to 2-hydroxybiphenel (2HBP) or other phenolic end products and gave blue color in the presence of Gibb's reagent. Depending on this result it can be suggested the involvement of the 4S pathway in the utilization of DBT via a specific cleavage of only the C-S bond by these isolates.In addition to the three isolates which gave positive results with Gibb’s assay, twelve efficient isolates (M3, M7, M16, M20, P4, P13, P14, S21-1, S22, S26, S34 and S37) could be utilized C ands. However, P13 isolate was the best one that cleaved both C-C and C-S bonds of DBT were candidate for identification. These fifteen isolates were identified as: Staphylococcus spp. [6 isolates, (including P13 isolate)], three of them were Staphylococcus aureus.Pseudomonas spp. (4 isolates), three of them were Pseudomonas aeruginosa. Micrococcus spp. (2 isolates), and one isolate for each genus of Neisseria sp., Corynebacterium sp. and Bacillus sp.  The DBT desulfurizing (P. aeruginosa M9, M19 and S25) and utilizing (P13) bacteria were grown in medium containing different carbon and sulfur sources. Highest growth of all isolates was obtained in medium containing glycerol and magnesium sulfate as carbon and sulfur sources respectively, because these compounds are simple sources forcarbon and sulfur.  To select one isolate from the three P. aeruginosa isolates (M9, M19 and S25), the concentration of the end product, resulted from culture grown with DBT was quantified by measuring the intensity of the corresponding blue color formed after addition of Gibb's reagent. The result showed that P. aeruginosaS25 was the efficient one for removing sulfur from DBT. The optimum conditions for utilization of DBT by P. aeruginosa S25 and P13 isolate were investigated. It was found that these conditions are growing these bacteria in basal salt medium (pH 8) containing 0.6 mM DBT and incubated with shaking (150 rpm) at 35 °C for three days. In order to determine the plasmid profile for P. aeruginosa (S25) and P13 isolate, a number of DNA extraction methods were used. Results showed that P. aeruginosa (S25) harbor small plasmid DNA bands, while there was no plasmid in P13 isolate.The GC/MS analysis of bacterial cultures (P. aeruginosa–S25 and P13 isolate) on DBT-Basal salt medium, indicated that 12.89 % of DBT was consumed (consumption of sulfur)  by the P. aeruginosa-S25, and the GC/MS analysis for the P13 isolate  showed that this isolate utilize the DBT as sulfur and carbon source. The GC/MS analysis of bacterial cultures on diesel-BSM indicated that all compounds that have sulfur atoms were degraded to less complex compounds by P. aeruginosa–S25 and P13 isolate.The sulfur content X-ray analysis of bacterial cultures indicated that these isolates utilize about 89 % and 34 % of total sulfur from DBT-BSM by P13
isolate and P. aeruginosa-S25 respectively. The percentage of sulfur consumption from diesel-BSM was about 5.9 % by P13 isolate and 5.4 % by P. aeruginosa-S25. Consequently both isolates showed a very good ability desulfurize and utilize DBT, they also showed good ability to consume sulfur from diesel.