Optimization of p-cresol biodegradation using novel bacterial strains isolated from petroleum hydrocarbon fallout

Abstract

Two potential p-cresol degrading bacterial strains were isolated from petroleum refinery wastewater and identified as Stenotrophomonas sp. (MF004205) strain DBK3 and Bacillus sp. (MF004206) strain DBK4 based on 16S rDNA gene sequencing. While DBK4 was able to utilize p-cresol up to 500 mg L−1 in about 2 days, isolated DBK3 restricted its growth till 600 mg L−1 initial p-Cresol concentration. Further studies were carried out using strain DBK3, which utilized p-cresol as the sole source of carbon. Growth kinetic studies were conducted to determine optimal environmental conditions for growth and biodegradation of p-cresol. Degradation of p-cresol at various preliminary concentrations were also studied at their optimum physiological conditions. 100 mg L−1 p-cresol was found to be the optimal pollutant concentration for growth whereas the ideal temperature and pH for growth and degradation were found to be 37 °C and 7.0 respectively. Microbial growth was monitored spectrophotometrically while residual p-cresol was measured via High Performance Liquid Chromatography (HPLC). Various growth kinetic parameters were estimated by fitting the experimental data to several established substrate inhibition kinetic models by non-linear regression analysis via MATLAB R2017b. The best fit was achieved using Haldane’s kinetic model (maximum growth rate, μmax = 0.1160 h−1 and inhibition constant, KI = 387 mg L−1). The experimental growth kinetic data also fitted reasonably well with Aiba, Yano and Webb model.