title: Bacterial degradation of tert-amyl alcohol proceeds via hemiterpene 2-methyl-3-buten-2-ol by employing the tertiary alcohol desaturase function of the Rieske nonheme mononuclear iron oxygenase MdpJ.
abstract: Tertiary alcohols, such as tert-butyl alcohol (TBA) and tert-amyl alcohol (TAA) and higher homologues, are only slowly degraded microbially. The conversion of TBA seems to proceed via hydroxylation to 2-methylpropan-1,2-diol, which is further oxidized to 2-hydroxyisobutyric acid. By analogy, a branched pathway is expected for the degradation of TAA, as this molecule possesses several potential hydroxylation sites. In Aquincola tertiaricarbonis L108 and Methylibium petroleiphilum PM1, a likely candidate catalyst for hydroxylations is the putative tertiary alcohol monooxygenase MdpJ. However, by comparing metabolite accumulations in wild-type strains of L108 and PM1 and in two mdpJ knockout mutants of strain L108, we could clearly show that MdpJ is not hydroxylating TAA to diols but functions as a desaturase, resulting in the formation of the hemiterpene 2-methyl-3-buten-2-ol. The latter is further processed via the hemiterpenes prenol, prenal, and 3-methylcrotonic acid. Likewise, 3-methyl-3-pentanol is degraded via 3-methyl-1-penten-3-ol. Wild-type strain L108 and mdpJ knockout mutants formed isoamylene and isoprene from TAA and 2-methyl-3-buten-2-ol, respectively. It is likely that this dehydratase activity is catalyzed by a not-yet-characterized enzyme postulated for the isomerization of 2-methyl-3-buten-2-ol and prenol. The vitamin requirements of strain L108 growing on TAA and the occurrence of 3-methylcrotonic acid as a metabolite indicate that TAA and hemiterpene degradation are linked with the catabolic route of the amino acid leucine, including an involvement of the biotin-dependent 3-methylcrotonyl coenzyme A (3-methylcrotonyl-CoA) carboxylase LiuBD. Evolutionary aspects of favored desaturase versus hydroxylation pathways for TAA conversion and the possible role of MdpJ in the degradation of higher tertiary alcohols are discussed.
authors.affiliation: Department of Environmental Microbiology, Helmholtz Centre for Environmental Research-UFZ, Leipzig, Germany.
authors.forename: Judith
authors.initials: J
authors.lastname: Schuster
authors.forename: Franziska
authors.initials: F
authors.lastname: Schäfer
authors.forename: Nora
authors.initials: N
authors.lastname: Hübler
authors.forename: Anne
authors.initials: A
authors.lastname: Brandt
authors.forename: Mònica
authors.initials: M
authors.lastname: Rosell
authors.forename: Claus
authors.initials: C
authors.lastname: Härtig
authors.forename: Hauke
authors.initials: H
authors.lastname: Harms
authors.forename: Roland H
authors.initials: RH
authors.lastname: Müller
authors.forename: Thore
authors.initials: T
authors.lastname: Rohwerder
mesh_terms: D020562:Betaproteobacteria / Q000201:enzymology*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D014450:Electron Transport Complex III / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D023061:Gene Order; D008969:Molecular Sequence Data; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism*; D000439:Pentanols / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D013230:Stearoyl-CoA Desaturase / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D000439:Pentanols; C037989:Rieske iron-sulfur protein; C032765:tert-amyl alcohol; D010105:Oxygenases; D013230:Stearoyl-CoA Desaturase; D014450:Electron Transport Complex III; C027250:3-hydroxy-3-methylbutene