Effect of introduced phthalate-degrading bacteria on the diversity of indigenous bacterial communities during di-(2-ethylhexyl) phthalate (DEHP) degradation in a soil microcosm

Four previously isolated di-butyl-phthalate (DBP) degraders were tested for their abilities to degrade di-(2-ethylhexyl) phthalate (DEHP). In aqueous medium supplemented with 100 mg/l of DEHP, both isolate G1 and Rhodococcus rhodochrous G2 showed excellent degradative activity; in three days they were able to degrade more than 97% of the added DEHP. Rhodococcus rhodochrous G7 degraded 32.5% of the added DEHP and Corynebacterium nitrilophilus G11 showed the least amount of DEHP degradation. The addition of surfactant Brij 30 at 0.1× critical micelle concentration (2 mg/l) significantly improved DEHP degradation by Rhodococcus rhodochrous G2 (more than 90% of the added DEHP was degraded within 24 hours), but slightly inhibited the degradation of DEHP by the isolate G1 and Rhodococcus rhodochrous G7. Based on the 16S rDNA sequence data, isolate G1 was identified as Gordonia polyisoprenivorans. Soil inhibited DEHP degradation by G. polyisoprenivorans G1; fourteen days after a second addition of DEHP, 11.5% of the total added DEHP (i.e., 243.4 μg/g soil) remained detectable. Changes in the bacterial community were monitored using denaturing gradient gel electrophoresis (DGGE) and respective dendrogram analysis. It is clear that DEHP and DEHP plus G. polyisoprenivorans G1 substantially affected the bacterial community structure in the soils. However, as the population of indigenous DEHP degraders increased in the DEPH-treated soil, its bacterial communities resembled those in the DEHP plus G. polyisoprenivorans G1-inoculated soil by Day 17.