Tolerance of selected plant species to petrogenic hydrocarbons and effect of plant rhizosphere on the microbial removal of hydrocarbons in contaminated soil

In this study, 11 plants (legumes, grasses, and crops) were screened for their ability to grow and survive in soil contaminated with 1 % diesel/oil mix (aliphatic hydrocarbons) or 1 % crude oil. Based on emergence, shoot length, root length, and root/shoot biomass ratio in contaminated soil, maize and wheat which showed the highest growth were selected for further investigation: a long-term phytoremediation study to evaluate the effect of maize and wheat on the microbial removal of hydrocarbons (1 % diesel/oil mix). The results showed that the presence of both maize and wheat in hydrocarboncontaminated soil led to a significant increase in the utilization of total petroleum hydrocarbon (TPH), from 57 % in the control soil to 72 and 66 % in soil planted with maize and wheat, respectively. Microbial community analysis using denaturing gradient gel electrophoresis (DGGE) showed that the presence of a plant rhizosphere resulted in changes in the structure of the soil microbial community. Sequencing of prominent bands revealed the presence of a few hydrocarbonoclastic fungi only in the contaminated soil planted with maize and wheat. In terms of specific hydrocarbonoclastic activity, DGGE analysis based on alkB genes showed that soils with maize and wheat had similar rates of hydrocarbonoclastic activity but distinct microbial communities in some instances. Most probable number quantitative polymerase chain reaction (MPN-qPCR) confirmed that the number of alkB gene copies in soil planted with maize and wheat increased about 20- and 16-fold, respectively, relative to the control soil. This study showed that fungal and alkB bacterial communities contribute to the rhizoremediation of petrogenic hydrocarbons.