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Abstract

This study aimed to isolate marine bacteria that can degrade phenanthrene and to investigate the effects of physical factors on the degradation of phenanthrene by the isolate. Two phenanthrene-degrading bacteria were isolated from seawater using an enrichment method. The isolated strains, designated PHPY and SK, degraded 99% of 500 mg/l phenanthrene in sterilized seawater within 15 and 10 days, respectively. In addition to phenanthrene, strain PHPY degraded anthracene, while strain SK could degrade fluorene. 16S rDNA-based phylogenetic analysis suggested that strains PHPY and SK might represent new genera of Sphingomonadaceae and Rhodobacteraceae, respectively. Studies on the effect of physical factors indicated that at temperatures of 30°C and 37°C, and pH 7.4-9.0, the strain PHPY could effectively grow and degrade phenanthrene. However, this strain could not grow at higher temperature or lower pH. Moreover, in the presence of NaCl at 22.79 g/l and even without added NaCl, strain PHPY was able to grow and degrade phenanthrene. PCR experiments with primers specific for large subunit of aromatic-ring-hydroxylating dioxygenase (bphA1f ) from Novosphingobium aromaticivorans F199 suggested that strain PHPY might possess genes for phenanthrene degradation that are not highly homologous to the genes in strain F199. Isolation of two new marine bacteria capable of degrading PAHs in this study confirmed that bacteria in genera Sphingomonadaceae and Rhodobacteraceae play an important role in the degradation of PAHs in marine environments.