Absence of the nahG-like gene caused the syntrophic interaction between Marinobacter and other microbes in PAH-degrading process

In this study, Marinobacter sp. N4 isolated from the halophilic consortium CY-1 was found to degrade phenanthrene as a sole carbon source with the accumulation of 1-Hydroxy-2-naphthoic acid (1H2N). With the assistance of Halomonas sp. G29, phenanthrene could be completely mineralized. The hpah1 and hpah2 gene cluster was amplified from the genome of strain N4, that were responsible for upstream and downstream of PAH degradation. Strain N4 was predicted for the transformation from phenanthrene to 1H2N, and strain G29 could transform the produced 1H2N into 1,2-dihydroxynaphthalene (1,2-DHN). The produced 1,2-DHN could be further transformed into salicylic acid (SALA) by strain N4. SALA could be catalyzed into catechol by strain G29 and further utilized by strains N4 and G29 via the catechol 2,3-dioxygenase pathway and catechol 1,2-dioxygenase pathway, respectively. NahG, encoding salicylate hydroxylase, was absent from the hpah2 gene duster and predicted to be the reason for 1H2N accumulation in the PAH-degrading process by pure culture of strain N4. The syntrophic interaction mode among Marinobacter and other microbes was also predicted. According to our knowledge, this is the first report of the PAH-degrading gene cluster in Marinobacter and the syntrophic interaction between Marinobacter and other microbes in the PAH-degrading process.