Biodegradation of benzene by pure and mixed cultures of <Emphasis Type="Italic">Bacillus</Emphasis> spp.

Benzene has a wide range of industrial applications, but it is also a major source of environmental pollution. The most eco-friendly/cost-effective method of remediation is biodegradation. In the present study, we used a variety of microbial strains in different combinations on a selection of substrate concentrations to determine the most effective degradation processes. Bacterial strains of pure culture (L₄, N₃, and N₆) were isolated from oil sludge in both Luria–Bertani buffer (LB) and nutrient broth media, and identified by 16S-rRNA analysis (≥98% similarity). The degradation experiments were performed using different combinations of bacterial strains (L₄, N₃, N₆, L₄ + N₃, L₄ + N₆, N₃ + N₆, and L₄ + N₃ + N₆) in modified carbon-free media with different concentrations of benzene as a carbon source (60, 100, and 160 mg l⁻¹) at 30 °C. The isolates of L₄ (Acc no: FJ686821), N₃ (FJ686825) and N₆ (FJ868628) were identified as Bacillus spp. using 16S-rRNA gene sequence analysis. All combinations of isolates have the capacity to degrade benzene. However, the L₄ + N₃ combination was more efficient than the other mixed or single cultures. In the presence of N₆ isolate, the degradation rate of benzene decreased, possibly due to inter- and/or intra species interaction amongst the bacteria. The kinetic parameters ‘K _m’ of the Lineweaver–Burk regressions conducted as part of this experiment showed that the lower the level of K _m was, the better the biodegradation achieved. The results of this study showed that the use of Bacillus strains in benzene decomposition is feasible. In addition, different strain combinations exhibited different degradation patterns, which are attributed to the most efficient mixed cultures of Bacillus spp.