Biotransformation of pentachlorophenol by an indigenous Bacillus cereus AOA-CPS1 isolated from wastewater effluent in Durban, South Africa.

Pentachlorophenol (PCP) is a recalcitrant biocide that bioaccumulates in the environment due to its persistent nature and has been listed as a priority pollutant due to its toxicological and health effects. In this study, a novel PCP-degrading Bacillus cereus strain AOA-CPS1 (BcAOA) was isolated from wastewater and characterized for PCP biotransformation in a batch reactor. The degradation kinetics were elucidated via substrate inhibition models, while PCP biotransformation was established by spectrophotometric and GC-MS analysis. BcAOA shared 95% sequence homology with Bacillus cereus strain XS2 and is closely related to some B. cereus strains which are previously reported to degrade PCP and other related pollutants. BcAOA degraded 74% of 350 mg l of PCP within 9 days in a batch culture. The biotransformation of PCP by BcAOA followed the first and zero-order kinetics at low and high PCP concentration, respectively, with biokinetic constants: maximum biotransformation rate (0.0996 mg l h); substrate inhibition constant (723.75 mg l); half-saturation constant (171.198 mg l) and R (0.98). The genes (pcpABCDE, cytochrome P450) encoding the enzymes involved in the biodegradation of PCP were amplified from the genomic DNA of BcAOA. Further, depending upon the genes amplified and identified metabolites using GC-MS, two different PCP biotransformation pathways were proposed in this study. Cloning and expression of the catabolic genes are underway to map out the concise pathway for PCP biotransformation by BcAOA.