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Mycobacterium austroafricanum IFP 2012 is able to slowly grow on methyl tert-butyl ether (MTBE), a fuel oxygenate widely used as a gasoline additive. The potential of M. austroafricanum IFP 2012 for aerobic MTBE degradation was investigated in the presence of a secondary carbon source, isopropanol. The strain was then tested for MTBE biodegradation at the laboratory-scale in a fixed-bed reactor using perlite as the matrix, and isopropanol was injected once a week to maintain M. austroafricanum IFP 2012 biomass inside the perlite bed. The biofilter was operated for 85 days at an influent flow rate of 20 ml/h by varying the MTBE concentration from 10 to 20 mg/l. The hydraulic retention time was fixed at 5 days. The removal of MTBE depended on the inlet MTBE concentration and a MTBE removal efficiency higher than 99% was obtained for MTBE concentrations up to 15 mg/l. A set of 16S rRNA gene primers specific for M. austroafricanum species was used to analyze the DNA extracted from the biofilter effluent in order to detect the presence of M. austroafricanum IFP 2012 and to estimate the effect of periodic injections of isopropanol on the release of the strain from the perlite bed. The results demonstrated that the injection of isopropanol served to maintain an active MTBE degrading biomass in the biofilter and that this system could be used to effectively treat MTBE contaminated groundwater., (Copyright 2008 S. Karger AG, Basel.)

Mycobacterium austroafricanum IFP 2012, which grows on methyl tert-butyl ether (MTBE) and on tert-butyl alcohol (TBA), the main intermediate of MTBE degradation, also grows on a broad range of n-alkanes (C2 to C16). A single alkB gene copy, encoding a non-heme alkane monooxygenase, was partially amplified from the genome of this bacterium. Its expression was induced after growth on n-propane, n-hexane, n-hexadecane and on TBA but not after growth on LB. The capacity of other fast-growing mycobacteria to grow on n-alkanes (C1 to C16) and to degrade TBA after growth on n-alkanes was compared to that of M. austroafricanum IFP 2012. We studied M. austroafricanum IFP 2012 and IFP 2015 able to grow on MTBE, M. austroafricanum IFP 2173 able to grow on isooctane, Mycobacterium sp. IFP 2009 able to grow on ethyl tert-butyl ether (ETBE), M. vaccae JOB5 (M. austroaafricanum ATCC 29678) able to degrade MTBE and TBA and M. smegmatis mc2 155 with no known degradation capacity towards fuel oxygenates. The M. austroafricanum strains grew on a broad range of n-alkanes and three were able to degrade TBA after growth on propane, hexane and hexadecane. An alkB gene was partially amplified from the genome of all mycobacteria and a sequence comparison demonstrated a close relationship among the M. austroafricanum strains. This is the first report suggesting the involvement of an alkane hydroxylase in TBA oxidation, a key step during MTBE metabolism.

A new Mycobacterium austroafricanum strain, IFP 2015, growing on methyl tert-butyl ether (MTBE) as a sole carbon source was isolated from an MTBE-degrading microcosm inoculated with drain water of an MTBE-supplemented gasoline storage tank. M. austroafricanum IFP 2015 was able to grow on tert-butyl formate, tert-butyl alcohol (TBA) and alpha-hydroxyisobutyrate. 2-Methyl-1,2-propanediol was identified as the TBA oxidation product in M. austroafricanum IFP 2015 and in the previously isolated M. austroafricanum IFP 2012. M. austroafricanum IFP 2015 also degraded ethyl tert-butyl ether more rapidly than M. austroafricanum IFP 2012. Specific primers designed to monitor the presence of M. austroafricanum strains could be used as molecular tools to detect similar strains in MTBE-contaminated environment.