Rhizodegradation of Phenanthrene, Anthracene and Pyrene by Augmenting Bacillus Cereus and Bacillus Subtilis Strains

Abstract

Rhizodegradation is one of the best methods for the effective removal of dangerous polycyclic aromatic hydrocarbons pollutants from soil. This is operative due to the high persistent, non-bioavailability nature of PAHs and combined, sequential reactions of bacteria present in rhizosphere of plants. We have conducted pot-culture method to study the degradation of three PAHs compounds namely phenanthrene, anthracene and pyrene in artificially contaminated soils of rhizosphere and non-rhizosphere soil treatments of blackgram(Vignamungo L.) that augmented by two potential PAHs degraders namely Bacillus cereus CPOU13 and Bacillus subtilis SPC14 isolated from naturally contaminated soils for 90days. HPLC studies revealed that degradation percentages of the three PAHs in treatments were more where selected strains augmented to the soil treatments over the non-augmented soils. The rhizosphere treatments that have augmented strains recorded more degradation percentages of phenanthrene, anthracene and pyrene over the rhizosphere treatments that were non-augmented. Pyrene, a high molecular weight PAHs degraded maximum to 96.24% in rhizosphere soil treatment that is augmented with the strains while moderate degradation of pyrene recorded in non-autoclaved soil treatments that contain natural microbial communities. The study of counting of bacterial populations during the experimental period revealed that the populations of the selected and other natural bacteria were gradually increased from the first day, reached maximum by 60days and became almost consistent in 90days in all the treatments. It was also observed that the populations of bacteria were high in rhizosphere treatments compared to the non-rhizosphere soil treatments. With these results it has been predicted that degradation of PAHs in rhizosphere soil treatments is closely associated with the increasing PAHs degrading bacterial populations of selected bacterial strains that may consume more quantity of PAHs for their metabolic activities in rhizosphere soils. Key words: Rhizodegradation, PAHs, HPLC, pot culture.