The methyl tert-butyl ether (MTBE) metabolic pathway was partially elucidated in Mycobacterium austroafricanum IFP 2012 by identifying the degradation intermediates. Several enzymatic activities were specifically induced during growth on MTBE. Among those required for the first steps of MTBE degradation to tent-butyl alcohol (TBA), the same monooxygenase was responsible for the oxidation of both MTBE and TBA, with a low affinity for TBA (Km = 1.1 mM). An esterase was involved in the hydrolysis of tert-butyl formate (TBF). The slowness of the degradation of MTBE by M. austroafricanum IFP 2012 was the result of complex interactions, especially the negative effect of W formed during MTBE oxidation on the MTBE/TBA moonoxygenase and the absence of TBA oxidation in the presence of residual MTBE. Moreover, concerning the downstream steps of MTBE metabolism, Cc(++) ions were required for the degradation of 2-hydroxyisobutyric acid (HIBA) formed by oxidation of TBA as shown by the low growth yield on HIBA in the absence of cobalt.
