Isolation and characterization of a 2-methylphenanthrene utilizing bacterium: identification of ring cleavage metabolites

Abstract

A bacterial strain capable of utilizing 2-methylphenanthrene (2-MP) as its sole source of carbon and energy for growth was isolated from creosote contaminated soil. The isolate was identified as a strain of Sphingomonas sp. and was designated strain JS5. Utilization of 2-MP by strain JS5 was demonstrated by an increase in bacterial biomass concomitant with a decrease of 2-MP in liquid mineral medium with this compound as sole source of carbon and energy. Growth yield indicated a 23% assimilation of 2-MP carbon. Washed-cell suspensions of strain JS5 incubated with 2-MP accumulated a major metabolite identified as 1-hydroxy-6-methyl-2-naphtoic acid, according to its UV, mass and NMR spectra, and a minor compound with HPLC R t and UV spectrum indistinguishable from 5-methylsalicylate. The identification of those metabolites, and the demonstration of 2,3-catechol dioxygenase activity in 2-MP induced cells show that the biodegradation of 2-MP by strain JS5 is initiated via dioxygenation and meta-cleavage of the non-methylated aromatic ring, and then proceeds by reactions similar to those reported for phenanthrene. Incubation of the strain with a MP-containing mixture from a pyrolytic fuel oil demonstrates that strain JS5 also acts on other methylated phenanthrenes.