Aerobic Degradation of 3-Chlorobenzoic Acid by Bacterial Strains Isolated from Petroleum Polluted Soils

Five bacterial isolates were isolated from soils polluted with petroleum waste deposition from Cairo Oil Refining Company, Al-Qalyubia, Egypt. These isolates were grown on five concentrations (20, 100, 500, 1000, 2000μM) of 3-chlorobenzoic acid (3-CBA) as a sole carbon and energy source. The abilities of these isolates to degrade this chloroaromatic compounds have been investigated. The growth (O.D), the extracellular protein secretion and release of Cl were determined after 1, 2, 3,4,5,6,7,15 and 21 days incubation for each concentration and strain. Degradation of 3-CBA was quantified by high performance liquid chromatography (HPLC). The results revealed that all isolates were able to degrade 100% of 20μM of 3-CBA. Isolate MAM-3, MAM-29 and E. cloaceae MAM-4 degrade 100% of 100 and 500μM of 3-CBA. Isolate MAM-3 and E. cloaceae MAM-4 showed remarkable decrease in 3-CBA degradation at higher concentrations. That isolate MAM-24 could removed a detectable amount of 3-CBA at high concentration than any of the other isolates did However, the qualitative determination of the degradation of 3-CBA by the parent strain MAM-24 and its mutant MAM24(9) which exposed to 4 kGy was determined after 24 and 48 hours by GC/MS. The results revealed that Bacillus mucilaginosus MAM-24 dechlorinated the chloroaromatic compound (3-chlorobenzoic acid) firstly to give benzoic acid. Benzoic acid may be reduced to give four intermediates (acetophenone, phenol, benzomethanol and/or benzeneethanol). The intermediates, phenol and benzomethanol were found after 24 and 48 hours in case of B. mucilaginosus MAM-24 and after 24 hours only in case of mutant MAM-24(9).