Biodegradation ability and dioxgenase genes of PAH-degrading Sphingomonas and Mycobacterium strains isolated from mangrove sediments

The biodegradation ability and initial dioxygenase genes of 21 PAH-degrading bacteria isolated from mangrove sediments were investigated. Most of the isolates belonged to the genera of Sphingomonas and Mycobacterium, and the other included Rhodococcus, Paracoccus and Pseudomonas. All the isolated Mycobacterium strains could completely degrade a mixture of polycyclic aromatic hydrocarbons (PAHs) comprising phenanthrene (Phe), fluoranthene (Fla) and pyrene (Pyr) in 14 days. On the other hand, the sphingomonads differed in the extent to which mixed PAHs were degraded from 3% to 79%. The co-culture of Sphingomonas and Mycobacterium strains enhanced the degradation and all three PAHs were completely removed in 7 days. Among the three PAHs, only Pyr was completely degraded by three Mycobacterium strains (SBSW, YOWG and SKEY), whereas Fla, and then Phe were degraded by these three and other isolates. The isolated Mycobacterium strains possessed the nidA gene encoding the initial dioxygenase required for Pyr degradation, while nahAc and phnAc were not detected in the sphingomonads.