Biodegradation of 2-ethylhexyl nitrate (2-EHN) by Mycobacterium austroafricanum IFP 2173

TL;DR

This study demonstrates that Mycobacterium austroafricanum IFP 2173 can biodegrade the pollutant 2-ethylhexyl nitrate (2-EHN), identifying a specific metabolite and proposing a pathway that explains its limited biodegradability.

Contribution

The paper identifies a novel metabolic pathway for 2-EHN degradation in M. austroafricanum IFP 2173, including the characterization of a key metabolite.

Findings

M. austroafricanum IFP 2173 effectively degrades 2-EHN.

A specific metabolite, 4-ethyldihydrofuran-2(3H)-one, was identified.

A proposed pathway explains the low biodegradability of 2-EHN.

Abstract

2-Ethyhexyl nitrate (2-EHN) is a major additive of fuel which is used to comply with the cetane number of diesel. Because of its wide use and possible accidental release, 2-EHN is a potential pollutant of the environment. In this study, Mycobacterium austroafricanum IFP 2173 was selected among several strains as the best 2-EHN degrader. The 2-EHN biodegradation rate was increased in biphasic cultures where the hydrocarbon was dissolved in an inert non-aqueous phase liquid (NAPL), suggesting that the transfer of the hydrophobic substrate to the cells was a growth-limiting factor. Carbon balance calculation as well as organic carbon measurement indicated a release of metabolites in the culture medium. Further analysis by gas chromatography revealed that a single metabolite accumulated during growth. This metabolite had a molecular mass of 114 Da as determined by GC/MS and was provisionally identified as 4-ethyldihydrofuran-2(3H)-one by LC-MS/MS analysis. Identification was confirmed by analysis of the chemically synthesized lactone. Based on these results, a plausible catabolic pathway is proposed whereby 2-EHN is converted to 4-ethyldihydrofuran-2(3H)-one, which cannot be metabolised further by strain IFP 2173. This putative pathway provides an explanation for the low energetic efficiency of 2-EHN degradation and its poor biodegradability.