Degradation Mechanism of Phenanthrene by the Halophilic Strain Altererythrobacter sp. Y3

Polycyclic aromatic hydrocarbons (PAHs) are relatively common in saline and hypersaline environments and pose a great threat to both the environment and human health. Biological treatment is an economically effective method for treating persistent organic pollutant pollution; however, traditional microbe species have limited ability to degrade PAHs in saline environments. In this study, strain Y3 was screened from the PAH-degrading bacterial consortium 5 H enriched in mixed saline soils in Shanxi and identified as belonging to the genus Altererythrobacter using 16 S rRNA sequencing. Using phenanthrene as the only carbon source and by changing the environmental factors, it was found that strain Y3 was highly tolerant to moderate to high salinity and highly efficient under neutral to weakly alkaline conditions. PAH-degrading genes, such as genes encoding ring hydroxylating dioxygenase (RHD) and gentisate 1,2-dioxygenase (G12O), were also annotated in the genome of strain Y3 and presented high novelty compared with other reported alleles. Moreover, the gene clusters of the PAH degradation pathway of strain Y3 were identified and annotated. Combined with the detected PAH-degrading intermediates, the degradation pathway of phenanthrene by strain Y3 was proposed. Phenanthrene was first activated by RHD and then further degraded through the G12O pathway. To our knowledge, this is the first report of phenanthrene degradation by Altererythrobacter sp. Y3 under high salinity. The PAH-degrading genes and pathways associated with Altererythrobacter are also reported for the first time. Strain Y3 is identified in this study to be able to degrade phenanthrene in saline and hypersaline environments, promoting the understanding of PAH degradation and providing a useful microbial resource for the remediation of PAHs in saline environments.