Effects of gasoline components on MTBE and TBA cometabolism by <Emphasis Type="Italic">Mycobacterium austroafricanum</Emphasis> JOB5 |
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Authors: | Alan J House Michael R Hyman |
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Institution: | (1) Department of Microbiology, North Carolina State University, Raleigh, NC 27695, USA; |
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Abstract: | In this study we have examined the effects of individual gasoline hydrocarbons (C5–10,12,14
n-alkanes, C5–8 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 C5–8
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 μM) 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. |
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