Effects of gasoline components on MTBE and TBA cometabolism by Mycobacterium austroafricanum JOB5

Abstract

In this study we have examined the effects of individual gasoline hydrocarbons (C(5-10,12,14) n-alkanes, C(5-8) isoalkanes, alicyclics [cyclopentane and methylcyclopentane] and BTEX compounds [benzene, toluene, ethylbenzene, m-, o-, and p-xylene]) on cometabolism of methyl tertiary butyl ether (MTBE) and tertiary butyl alcohol (TBA) by Mycobacterium austroafricanum JOB5. All of the alkanes tested supported growth and both MTBE and TBA oxidation. Growth on C(5-8) n-alkanes and isoalkanes was inhibited by acetylene whereas growth on longer chain n-alkanes was largely unaffected by this gas. However, oxidation of both MTBE and TBA by resting cells was consistently inhibited by acetylene, irrespective of the alkane used as growth-supporting substrate. A model involving two separate but co-expressed alkane-oxidizing enzyme systems is proposed to account for these observations. Cyclopentane, methylcyclopentane, benzene and ethylbenzene did not support growth but these compounds all inhibited MTBE and TBA oxidation by alkane-grown cells. In the case of benzene, the inhibition was shown to be due to competitive interactions with both MTBE and TBA. Several aromatic compounds (p-xylene > toluene > m-xylene) did support growth and cells previously grown on these substrates also oxidized MTBE and TBA. Low concentrations of toluene (<10 microM) stimulated MTBE and TBA oxidation by alkane-grown cells whereas higher concentrations were inhibitory. The effects of acetylene suggest strain JOB5 also has two distinct toluene-oxidizing activities. These results have been discussed in terms of their impact on our understanding of MTBE and TBA cometabolism and the enzymes involved in these processes in mycobacteria and other bacteria.

Oxidation of Cyclic Ethers by Alkane‐Grown Mycobacterium vaccae JOB5

“…These enzymes are again potentially directly associated with the alkane-oxidizing activity of this strain. We have also recently demonstrated that MTBE can be oxidized by strain JOB5 after growth on most shorter chain (< C 8 ) normal and branched alkanes (House & Hyman, 2010). These physiological studies suggest that the same monooxygenase enzyme initiates the oxidation of MTBE, TBA, and all of the growth-supporting ≤ C 8 alkanes.…”

“…Cells grown on all of the alkanes tested consumed all of these ethers and, in most instances, this activity was strongly inhibited (>90 percent) by the presence of acetylene (Exhibit 1). This effect of acetylene suggested the ethers were all oxidized by SCAM (House & Hyman, 2010). The role of SCAM activity in ether oxidation is further supported by the much lower levels of ether-oxidizing activity in cells grown on dextrose-containing medium (Exhibit 1).…”

“…Our own studies with strain JOB5 have focused on defining the pathway of oxidation of MTBE by this bacterium (Smith et al, 2003a) and determining the range of alkane growth substrates that support this activity (House & Hyman, 2010;Johnson et al, 2004). Although this strain does not grow on MTBE, the cometabolic oxidation of this compound involves extensive, if not complete, oxidation by propane-grown cells.…”

“…These physiological studies suggest that the same monooxygenase enzyme initiates the oxidation of MTBE, TBA, and all of the growth-supporting ≤ C 8 alkanes. This enzyme has been described as a short-chain alkane monooxygenase (SCAM) to differentiate it from another monooxygenase (long-chain alkane monooxygenase [LCAM]) that appears to initiate oxidation of long chain alkane growth substrates but does not oxidize MTBE (House & Hyman, 2010). As a continuation of our interest in ether biodegradation, in this study we examined the degradation of cyclic ethers by strain JOB5 grown on several short-chain alkanes that all support rapid rates of MTBE oxidation (House & Hyman, 2010).…”

Effect of benzene and ethylbenzene on the transcription of methyl-tert-butyl ether degradation genes of Methylibium petroleiphilum PM1

“…A pure culture designated PEL-B201 co-metabolized MTBE following growth on benzene; however, MTBE degradation was severely inhibited in the presence of benzene at concentrations as low as 0.15 mg l À1 presumably due to competitive inhibition (Koenigsberg et al, 1999). Benzene and ethylbenzene have also been shown to inhibit MTBE oxidation in an alkane-grown pure culture of Mycobacterium austroafricanum JOB5 (House & Hyman, 2010). In contrast, other investigations of interactions between BTEX and MTBE in continuous reactors and mixed bacterial consortia showed no impacts of BTEX compounds on MTBE degradation (Pruden et al, 2001;Sedran et al, 2002).…”