Biodegradation of di-n-butyl phthalate by a newly isolated Diaphorobacter sp. strain QH-6

Di-n-butyl phthalate (DBP), one of the most popular phthalic acid esters (PAEs), is commonly found in wastewater treatment plant. In this study, a bacterial strain capable of using DBP as sole carbon and energy source was isolated from activated sludge. This strain was identified as Diaphorobacter sp., designated as QH-6, based on the 16S rRNA and gyrB gene sequence analysis. For the first time, we studied the biodegradation ability of PAEs by genus Diaphorobacter. The high performance liquid chromatography (HPLC) analysis revealed that the optimum conditions for DBP degradation were pH 7.0 to 8.0, temperature 30 to 35°C, and agitation rate 150 to 225 r/min. Under these conditions, 500 mg/L of DBP could be completely degraded with a half-life of 5.20 h. We investigated the effects of heavy metals (Cr6+ and Cu2+) on the DBP degradation. The results demonstrated that the heavy metals at a wide concentration range of 5 to 30 mg/L can restrain the DBP degradation. Furthermore, substrate utilization tests showed QH-6 can also utilize other PAEs and the degradation intermediates.   Key words: Diaphorobacter sp., dibutyl phthalate, biodegradation, heavy metal.