MINI-REVIEW Enzymes and genes involved in the aerobic biodegradation of methyl tert-butyl ether (MTBE) Nicolas Lopes Ferreira & Cédric Malandain & Françoise Fayolle-Guichard Received: 3 April 2006 / Revised: 4 May 2006 / Accepted: 4 May 2006 / Published online: 28 June 2006 # Springer-Verlag 2006 Abstract Fuel oxygenates, mainly methyl tert-butyl ether (MTBE) but also ethyl tert-butyl ether (ETBE), are added to gasoline in replacement of lead tetraethyl to enhance its octane index. Their addition also improves the combustion efficiency and therefore decreases the emission of pollu- tants (CO and hydrocarbons). On the other hand, MTBE, being highly soluble in water and recalcitrant to biodegra- dation, is a major pollutant of water in aquifers contami- nated by MTBE-supplemented gasoline during accidental release. MTBE was shown to be degraded through cometabolic oxidation or to be used as a carbon and energy source by a few microorganisms. We have summarized the present state of knowledge about the microorganisms involved in MTBE degradation and the MTBE catabolic pathways. The role of the different enzymes is discussed as well as the rare and recent data concerning the genes encoding the enzymes involved in the MTBE pathway. The phylogeny of the microorganisms isolated for their capacity to grow on MTBE is also described. Introduction Petroleum compounds are the most widely used chemicals worldwide and their use requires numerous transportation and storage facilities. Such an intensive and disseminated use leads to numerous cases of spillage resulting in groundwater contamination (Johnson et al. 2000). Petro- leum compounds are actually the most frequently found contaminants of groundwater and among them is gasoline (world consumption in 2003–2004 was 11,675 Mt). Gaso- line is a complex mixture of numerous individual native chemicals. Other chemicals are also added to gasoline to meet specific requirements. For instance, lead tetraethyl has been added to gasoline for 50 years to reach the specifications regarding the octane index. In the 1970s, lead was banned from gasoline formulation because of its detrimental effect on catalytic converters fitted on exhaust pipes. Oxygenates were then chosen by refiners in replacement of lead because of their high octane index. Moreover, the use of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), or tert-amyl methyl ether (TAME) was also of interest because they reduced the emission of pollutants (CO and hydrocarbons) in exhaust gases. MTBE, added to gasoline at a maximal concentration of 15% (on a volume basis), was mostly used, with ETBE being also used in Europe (for details, see Fayolle and Monot 2005). The high solubility of these compounds (ca. 40 and 10 g l -1 for MTBE and ETBE, respectively) makes them the most water-soluble compounds of reformulated gasoline. The environmental impact of ether fuels on groundwater was not estimated before their utilization. Studies carried out years after the beginning of their current use showed that MTBE was detected at various concentrations in numerous aquifers in the USA (Johnson et al. 2000). When an MTBE-supplemented gasoline is spilled, the plumes generated by MTBE are indeed much larger than those generated by benzene (water solubility=1.755 g l -1 ). According to Wilson (2003), the retardation factor (ratio of water speed to pollutant speed) was 1.8 for benzene and 1.1 for MTBE, which means that MTBE migrates practically as rapidly as the aquifer. This is the consequence of (1) its low adsorption onto organic matter, (2) its high solubility, and (3) its recalcitrance to biodegradation. Thus, the half-life of Appl Microbiol Biotechnol (2006) 72:252–262 DOI 10.1007/s00253-006-0494-3 N. Lopes Ferreira : C. Malandain : F. Fayolle-Guichard (*) Biotechnology and Biomass Chemistry Department, Institut Français du Pétrole, 1-4 avenue de Bois-Préau, 92852 Rueil-Malmaison, France e-mail: francoise.fayolle@ifp.fr