Catabolic enzyme activity and kinetics of pyrene degradation by novel bacterial strains isolated from contaminated soil

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Polycyclic aromatic hydrocarbons (PAHs) with high molecular weight are difficult to degrade owing to their chemical structure and stability. This study reports degradation of pyrene by two potent Gram-positive bacterial strains isolated from petroleum-contaminated soil from Bijwasan supply location of Bharat Petroleum Corporation Limited (BPCL), India. The bacteria were identified as Kocuria flava and Rhodococcus pyridinivorans based on 16S rRNA gene sequencing. The degradation of pyrene, enzyme activity of Catechol 2,3-dioxygenase (C23O), dehydrogenase, and peroxidase, and the rate kinetics of degradation were investigated using the isolated bacteria. K. flava and R. pyridinivorans could degrade pyrene with an efficiency of 53.8% and 56.2%, within 15 days of incubation period under laboratory conditions. The consortium revealed 56.4% degradation of pyrene indicating that there is no significant synergistic/inhibitive effect. The activity (maximum on 9th day of incubation) of peroxidase enzyme (9.4 × 10 −4 and 16.9 × 10 −4 μ M/ml/min) was followed by dehydrogenase (2.6 × 10 −4 and 2.3 × 10 −4 μ M/ml/min) and C23O (2.2 × 10 −4 and 2.8 × 10 −4 μ M/ml/min) for K. flava and R. pyridinivorans , respectively, suggesting their involvement in ring-cleavage, diol-formation, and subsequent oxidation of the intermediates. Analysis of rate kinetics exhibited degradation of pyrene to be the first order reaction indicating that an increase in initial concentration of pyrene will not compromise with the ability of studied bacteria towards degradation. Analysis of initial and final concentration of treated media over HPLC confirmed significant pyrene degradation within 15 days. The study concludes that K. flava and R. pyridinivorans can play an active role in remediation of hydrocarbon-contaminated sites. • Degradation of pyrene by K. flava and R. pyridinivorans reported for first time. • C23O enzyme regulates ring cleavage and peroxidase oxidises pyrene-intermediates. • No inhibitory effect of K. flava and R. pyridinivorans over each other.