Rhizodegradation of polycyclic aromatic hydrocarbons (pahs) by Bacillus cereus CPOU13

We conducted pot-culture experiments to study the rhizodegradation of three PAHs compounds namely phenanthrene, anthracene and pyrene with blackgram plants. PAHs compounds were accurately weighed then added to experimental soils viz., rhizosphere and non-rhizosphere sets and made the final concentration of PAHs 600ppm. Fresh cultures of PAHs degrading bacteria strain, B. cereus CPOU13 added to the soil and made final concentration of the strain 3.3 × 104 CFU, then the experiment was conducted for 90days. The PAHs compounds were extracted finally from soil samples after the 90days and their concentrations were determined using HPLC methods. High degradation of the PAHs was observed in the rhizosphere soil treatments over the non-rhizosphere soils. The strain from rhizosphere and non-rhizosphere soil treatments recorded high degradation when compared to natural microflora in non-autoclaved soils. Inrespect to the phenanthrene the strain recorded 83.03% of degradation in autoclaved rhizosphere soils. Anthracene was degraded up to 76.10% in the treatment of autoclaved rhizosphere soil by the strain and it was slightly decreased in non-autoclaved rhizosphere soil. The strain degraded pyrene up to 82.1% in autoclaved rhizosphere soil and its low degradation observed in non-rhizosphere soil treatments. During this 90days of experiment population of the bacteria was enumerated in the treatment soils at regular time intervals viz., 0, 15, 30, 60 and 90days using serial dilution technique. Population of the bacteria was increased more in rhizosphere treatments over the non-rhizosphere treatments and it gradually increased from the 0th day and reached at maximum by 60days. Afterwards, slight decrease was observed in bacterial population. Hence this study determined that the PAHs degradation under rhizodegradation perhaps associated with the increasing population of PAHs degrading strain and its increased biological activities.