BTEX- and naphthalene-degrading bacterium Microbacterium esteraromaticum strain SBS1-7 isolated from estuarine sediment

In this study, a non-pathogenic, BTEX-degrading Microbacterium esteraromaticum SBS1-7 was isolated from estuarine sediment in Thailand via an enrichment technique. M. esteraromaticum SBS1-7 was able to degrade all six BTEX components, in both liquid medium and soil slurry system, when BTEX was supplied as an individual component or a mixture. It exhibited a high level of tolerance towards a wide range of hydrocarbons and also utilized alkanes and naphthalene. Detection of metabolites produced during BTEX and naphthalene degradation revealed highly extensive biodegradation pathways used by M. esteraromaticum SBS1-7. Toluene was metabolized via activities of both monooxygenase (toluene 4-monooxygenase or T4MO) and dioxygenases (toluene dioxygenase or TDO and naphthalene 1,2-dioxygenase or NDO). Benzene was metabolized via phenol, possibly by an activity of T4MO. Ethylbenzene was converted into styrene and 1-phenethyl alcohol by a well-documented activity of NDO. Dioxidation of ethylbenzene, possibly by ethylbenzene dioxygenase or EBDO, was also found. All xylene isomers were converted into their corresponding alcohols via an activity of NDO while naphthalene was metabolized via dioxidation reaction by the same enzyme. This study is, by far, the first direct evidence of BTEX biodegradation by a non-pathogenic, rhizosphere bacterium M. esteraromaticum.