Biodegradation of Methyl tert -Butyl Ether and Other Fuel Oxygenates by a New Strain, Mycobacterium austroafricanum IFP 2012

Abstract

A strain that efficiently degraded methyl tert-butyl ether (MTBE) was obtained by initial selection on the recalcitrant compound tert-butyl alcohol (TBA). This strain, a gram-positive methylotrophic bacterium identified as Mycobacterium austroafricanum IFP 2012, was also able to degrade tert-amyl methyl ether and tert-amyl alcohol. Ethyl tert-butyl ether was weakly degraded. tert-Butyl formate and 2-hydroxy isobutyrate (HIBA), two intermediates in the MTBE catabolism pathway, were detected during growth on MTBE. A positive effect of Co 2؉ during growth of M. austroafricanum IFP 2012 on HIBA was demonstrated. The specific rate of MTBE degradation was 0.6 mmol/h/g (dry weight) of cells, and the biomass yield on MTBE was 0.44 g (dry weight) per g of MTBE. MTBE, TBA, and HIBA degradation activities were induced by MTBE and TBA, and TBA was a good inducer. Involvement of at least one monooxygenase during degradation of MTBE and TBA was shown by (i) the requirement for oxygen, (ii) the production of propylene epoxide from propylene by MTBE-or TBAgrown cells, and (iii) the inhibition of MTBE or TBA degradation and of propylene epoxide production by acetylene. No cytochrome P-450 was detected in MTBE-or TBA-grown cells. Similar protein profiles were obtained after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of crude extracts from MTBE-and TBA-grown cells. Among the polypeptides induced by these substrates, two polypeptides (66 and 27 kDa) exhibited strong similarities with known oxidoreductases.Methyl tert-butyl ether (MTBE) has been incorporated in reformulated gasoline at concentrations up to 15% (vol/vol) to replace lead tetraethyl in order to comply with the octane index and to reduce the polluting emissions in exhaust gases. Other oxygenates, such as ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME) and their corresponding alcohols, tert-butyl alcohol (TBA) and tert-amyl alcohol (TAA), can play the same role regarding the octane index. MTBE is the dominant fuel oxygenate (38), with a worldwide production capacity of around 25 million tons. Because of its widespread use and the high frequency of underground tank leakage (35), this compound is now the second most commonly detected contaminant in urban groundwater in the United States (23, 42). In Europe, detectable levels of MTBE in rivers have also been reported (1).The persistence of MTBE in the environment can be ascribed, on the one hand, to its physicochemical properties (i.e., its low adsorption on organic matter and its high solubility in water) and, on the other hand, to its molecular structure (it has both an ether bond and high steric hindrance, which makes it recalcitrant to microbial degradation).Early reports based on microcosms having different origins mentioned the recalcitrance of MTBE and TAME (22) MTBE cometabolism was demonstrated by using propanegrown bacteria (35), an n-butane-grown fungus (17), camphorgrown Pseudomonas putida CAM (36), pentane-grown Pseudomonas aeruginosa (14), ETBE-grown Rhodococcus ruber IFP 2007 (...

n-Alkane assimilation and tert-butyl alcohol (TBA) oxidation capacity in Mycobacterium austroafricanum strains

“…Johnson and Hyman (2006) recently demonstrated a new capacity of P. putida GPo1 to also grow on the gaseous n-alkanes, propane and butane, confirming the broad alkane spectrum of the alkane hydroxylase in this strain. Among the strains of M. austroafricanum examined in this study, three of them were able to use C 2 to C 16 n-alkanes as their sole carbon and energy source: M. austroafricanum IFP 2012 and IFP 2015, isolated for their capacity to grow on TBA and MTBE (François et al 2002; Lopes Ferreira et al tuberculosis H37Rv alkB (accession numbers: X58890 and Z95121, respectively) and of P. putida GPo1 (accession numbers: AJ249825 and CAB54050, respectively) were included for comparison. The topology of the alkB sequences of mycobacteria was obtained by TopPred prediction (Claros and von Heijne 1994) and compared to the topology of P. Putida GPo1 alkB gene (Van Beilen et al 1992).…”

“…Moreover, a few strains were able to grow on MTBE and therefore on TBA; Methylibium petroleiphilum PM1 (Hanson et al 1999;Nakatsu et al 2006), Hydrogenophaga flava ENV735 (Hatzinger et al 2001), M. austroafricanum IFP 2012 (François et al 2002) and, more recently, M. austroafricanum IFP 2015 (Lopes Ferreira et al 2006b) and Aquincola tertiaricarbonis L10 (Lechner et al 2007). These strains have been studied at the physiological level, but the genes and enzymes involved in the oxidation of MTBE and in the oxidation of TBA are still unknown.…”

“…M. austroafricanum IFP 2012 was isolated for its capacity to grow on TBA. Both MTBE and TBA were inducers of MTBE and TBA degradation activity (François et al 2002). More recently, M. austroafricanum IFP 2015 was isolated for its capacity to grow on MTBE (Lopes Ferreira et al 2006b).…”

Genes Involved in the Degradation of Ether Fuels by Bacteria of the Mycobacterium/Rhodococcus Group

“…In recent years, however, several studies have shown that bacterial [1][2][3][4][5][6][7] and fungal [8] isolates are capable of breaking the ether bond of ether fuels, generating tert-butyl alcool (TBA) in the process. TBA can then be further metabolized, either by the same microorganism [2,[5][6][7] or by other microorganisms living in the same natural or artificial consortium [9][10][11].…”

Éter típusú üzemanyag-adalékok mikrobiális bontása

“…A Mycobacterium austroafricanum IFP 2012 jelű törzset TBA-bontóként izolálták, de a későbbiekben igazolták, hogy MTBE, TAME és TAA bontására is képes, ETBE-n viszont gyengén nő [112]. Az MTBE lebontási köztitermékei közül a TBF-et, a TBA-t, az MPD-t, a 2-HIBA-t és az acetont azonosították.…”