DISTRIBUTION AND REGULATION OF CYTOCHROMES P450 INVOLVED IN FUEL OXYGENATES DEGRADATION
Résumé
We compared the degradation capacity towards fuel oxygenates (methyl tert-butyl ether or MTBE, ethyl tert-butyl ether or ETBE and tert-amyl methyl ether or TAME) of R. ruber IFP 2001, R. zopfii IFP 2005, Mycobacterium sp. IFP 2009 and R. erythropolis NI86/21. Strains IFP 2001, IFP 2005 and IFP 2009 are able to grow on ETBE due to the activity of a cytochrome P450, CYP249 and strain NI86/21 was able to grow on an herbicide, S-ethyl dipropylthiocarbamate or EPTC due to the activity of another cytochrome P450, CYP116. We demonstrated that the cytochrome involved in EPTC biodegradation was also able to degrade ETBE to tert-butyl alcohol (TBA). All the strains harbouring CYP249 were also able to degrade MTBE and TAME but the preferred substrate was ETBE in all cases with specific activity measured after growth on ETBE of 2.1, 3.5 and 1.6 mmoles ether g-1dry weight h-1 for strain IFP 2001, IFP 2005 and IFP 2009, respectively. We also investigated the induction of the eth genes in the R. ruber IFP2001 and determined that only ETBE was able to induce the system and that this induction was inhibited in presence of easier substrate, implying a catabolite repression system. Using alignments, we spotted several mutations in the regulators EthR and the cytochromes EthB itself which might explain the differences observed in the degradation rates. Our results show that the specificity of the eth cytochrome system is rather due to the regulator itself than to the specificity of the cytochrome.