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

J Bacteriol. 2012 Mar;194(5):972-81. doi: 10.1128/JB.06384-11. Epub 2011 Dec 22.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Betaproteobacteria / enzymology*
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / genetics
  • Electron Transport Complex III / genetics
  • Electron Transport Complex III / metabolism*
  • Gene Deletion
  • Gene Order
  • Molecular Sequence Data
  • Oxygenases / genetics
  • Oxygenases / metabolism*
  • Pentanols / metabolism*
  • Sequence Analysis, DNA
  • Stearoyl-CoA Desaturase / metabolism

Substances

  • DNA, Bacterial
  • Pentanols
  • Rieske iron-sulfur protein
  • tert-amyl alcohol
  • Oxygenases
  • Stearoyl-CoA Desaturase
  • Electron Transport Complex III
  • 3-hydroxy-3-methylbutene

Associated data

  • GENBANK/JQ001939
  • GENBANK/JQ062962