Isolation and genetic characterization of phenol-utilizing marine bacteria and their phenol degradation pathway

Phenolic compounds are widely distributed toxic pollutants in seawater, and their effective degradation is very important for bioremediation programs. In this study, nine phenol-degrading bacteria were isolated from seawater samples, which were collected from the coastal areas of Japan. Besides the enrichment substrate phenol, all isolates could utilize at least one isomer of cresol as the sole source of carbon. A 16S rRNA gene sequence analysis indicated that all strains were affiliated with the class Gammaproteobacteria, four strains were closely related to Spongiibacter, four were closely related to Marinobacter, and one was closely related to Photobacterium. During growth on phenol, all isolates produced a yellow product, and a whole-cell study indicated that it was an extradiol meta-ring cleavage product of catechol, 2-hydroxymuconate semialdehyde. Phylogenetic analysis revealed that the partial gene encoding the largest subunit of the multicomponent phenol hydroxylase of the isolates was similar to that of terrestrial bacteria, thereby suggesting that phenol is converted into catechol by marine bacteria. We also suggest that horizontal transfer of the gene may occur not only among marine bacteria but also between the genera Marinobacter and Pseudomonas.