Characterization and kinetic study of PAH–degrading Sphingopyxis ummariensis bacteriaisolated from a petrochemical wastewater treatment plan

The expansion of a microbial bank for the degradation of polycyclic aromatic hydrocarbons (PAHs) is crucial for removal of these persistent pollutants. In this study, five gram–negative, aerobic, non–fermentative bacterial strains (III–R3, IV–P11, IV–P13, IV–R13, and V–P18) were isolated from the activated sludge of a petrochemical wastewater treatment plant using enrichment protocol based on phenanthrene. The isolates were capable of utilizing phenanthrene, anthracene, and pyrene as a sole carbon and energy source in an aerobic batch aqueous system. The PAHs biodegradation yields were evaluated by gas chromatography and the bacterial isolates were identified using the 16S rRNA sequencing method. A first–order kinetic model provided the best fit to the phenanthrene degradation profiles with a correlation coefficient value of 0.95–0.98. The phenanthrene biodegradation rate constants and half–lives were measured at the range 0.653–0.878 day–1and 0.79–1.06 day, respectively. Lower values of Anthracene degradation resulted with the isolates of the current study, while a relatively high percentage of the removal of Pyrene was obtained by some of the isolates. The data obtained in this study shows that bacterial isolates have degradation preference overMycobacterium sp. and Pseudomonas aeruginosa; and they are comparable withPseudomonas stutzeri, Sphingomonas sp., and microbial consortium applied by other researchers. Analysis of the 16S rDNA gene sequence, when compared with the GenBank, indicates that all the strains belong to the genus Sphingopyxiswith the nearest type strain being Sphingopyxis ummariensis UI2 (MTCC 8591T). It is the first time that Sphingopyxis ummariensis is reported for its capability in the degradation of PAHs

Keywords:

Polycyclic aromatic hydrocarBons (PAHs) , Phenanthrene , Biodegradation , Kinetics , Sphingopyxis ummariensis