Study of the dynamic of Bacillus species during of oil contaminated soil by PCR-DGGE

Bioremediation is an effective, inexpensive and environmental friendly manner for removing oil pollutions. Studding the biodiversity of indigenous microorganisms and their function is very important for bioremediation strategy selection and performance. This study was aimed to investigate the rule of Bacillus species in bioremediation of diesel contaminated soil.
Soil microcosms were prepared by adding 2 and 4% (W/W) of diesel to the soil. A control microcosm without diesel contamination was also set up. Microcosms were amended with nitrogen and phosphate sources and water (20%) and in a six month study period and parameters includingdiesel degradation, heterotrophic bacterial count and Bacillus spp. diversity by 16S rRNA PCR-DGGE were studied.
The results showed that in 2% microcosm up to 50% and in 4% microcosm up to 44.44% of diesel were degraded after six months. The increase of bacterial count was completely coincided with the highest diesel removal rate. The count of heterotrophic bacteria in 2 and 4% microcosms was elevated from 2Í108 to 2Í1011 and 2Í1012 at the highest point, respectively. Accordingly, introduction of the diesel stimulated the native soil bacteria and the amount of pollution was determinative in bioremediation efficiency.
Discussion and Comparison of the pattern of DGGE bands variation between the microcosms showed that by entry of the contaminant into the soil, the diversity of Bacillus species was increased, indicating that Bacillus species has a particular role in diesel degradation. Simultaneous with decline of the pollution and microbial count of the soil, diversity of DGGE bands was decreased. Out of these findings we may conclude that addition of diesel as a carbon source to the soil increases the Bacillus spp. diversity at the beginning of bioremediation and afterwards by elimination of the pollutant, the diversity decreases gradually and shifts back to its original structure