Biodegradation of phthalate isomers by newly isolated Klebsiella variico SY1 and its functional genomic analysis

Phthalate isomers (ortho-, meta-, and para-) are important industrial aromatic dicarboxylic acids and key in-termediates of pollutants degradation such as waste polyethylene terephthalate (PET) and plasticizers. Recently, microbial treatment of such pollutants has been received much attention. In this study, Klebsiella variico SY1, which could simultaneously degrade three phthalate isomers, was isolated from river sludge. The degradation priority order of the three phthalate isomers was phthalate (PA), terephthalate (TPA) and isophthalate (IPA), and the tolerant concentration could reach 5500 mg/L. The degradation results showed that SY1 degraded 3000 mg/ L of three isomers at the maximum rates of 186.38 mg/Lah for TPA and 195.90 mg/Lah for IPA, respectively. The analysis of comparative genome, key enzyme activity, gene expression and degradation intermediates, showed that SY1 initially degraded these three phthalate isomers to a common intermediate protocatechuic acid (PCA), and then accomplished a subsequent degradation through a bifurcated pathway. In addition, it was surmised that the ben gene cluster might also be involved in the degradation of phthalate isomers. In summary, Klebsiella variico SY1 was demonstrated as a chassis cell able to biodegrade phthalates and their derived contaminants due to its high degradation efficiency and tolerance against the three phthalate isomers.