Intensification of pyrene degradation by native Candida tropicalis MTCC 184 with sonication: Kinetic and mechanistic investigation

Abstract

Candida tropicalis is a well–known yeast strain for degradation of polycyclic aromatic hydrocarbons. In this paper, we have reported intensification of biodegradation of pyrene with sonication. This study has also attempted to deduce the mechanistic features of intensification induced by sonication. The initial statistical optimization of biodegradation parameters revealed following results: pH = 6, temperature = 33ºC, agitation speed = 164 rpm and % inoculum = 8.07% v/v and pyrene degradation of ~53%. Investigations of the yeast growth pattern on a wide range of salt concentrations revealed that the strain could withstand upto 20% NaCl concentration. The kinetics of pyrene removal followed the 1st order kinetics with rate constant of 0.0667 day−1 and half–life of 10.39 days. Optimum sonication duty cycle using flow cytometry was 10% with negligible cell death. Exposure of reaction mixture to 33 kHz sonication in log phase resulted in 30% augmentation in pyrene elimination. The expression of overall proteins present in the samples were examined by SDS–PAGE. This analysis revealed overexpression of catechol 2,3–dioxygenase (–meta route metabolism) in the ultrasound–treated samples. FE–SEM micrographs did not show any cell rupture or damage during sonication.