Biodegradation of di-n-butyl phthalate by an isolated Gordonia sp. strain QH-11: Genetic identification and degradation kinetics

Di-n-butyl phthalate (DBP) is one of the most widely used phthalic acid esters (PAEs), which have shown increasing environmental concerns worldwide. A bacterial strain designated as QH-11, was isolated from activated sludge and found to be capable of utilizing DBP as carbon and energy sources for growth. 16S rRNA and gyrb gene sequence analysis revealed that strain QH-11 was most closely related to Gordonia sp. Kinetics studies of DBP degradation by the strain QH-11 revealed that DBP depletion curves fit with the modified Gompertz model (R(2)>0.98). Meanwhile, substrate utilization tests showed that strain QH-11 could utilize other common PAEs and also the main intermediate product phthalic acid (PA). A gene encoding the large subunit of the phthalate dioxygenase, which is responsible for PA degradation, was successfully detected in strain QH-11. Furthermore, the results of reverse transcription quantitative PCR demonstrate that mRNA expression level of phthalate dioxygenase increased significantly after strain QH-11 was induced by DBP and PA.