Beschreibung:
<jats:title>ABSTRACT</jats:title>
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The betaproteobacteria “
<jats:named-content content-type="genus-species">Aromatoleum aromaticum</jats:named-content>
” pCyN1 and “
<jats:named-content content-type="genus-species">Thauera</jats:named-content>
” sp. strain pCyN2 anaerobically degrade the plant-derived aromatic hydrocarbon
<jats:italic>p</jats:italic>
-cymene (4-isopropyltoluene) under nitrate-reducing conditions. Metabolite analysis of
<jats:italic>p</jats:italic>
-cymene-adapted “
<jats:named-content content-type="genus-species">A. aromaticum</jats:named-content>
” pCyN1 cells demonstrated the specific formation of 4-isopropylbenzyl alcohol and 4-isopropylbenzaldehyde, whereas with “
<jats:named-content content-type="genus-species">Thauera</jats:named-content>
” sp. pCyN2, exclusively 4-isopropylbenzylsuccinate and tentatively identified (4-isopropylphenyl)itaconate were observed. 4-Isopropylbenzoate in contrast was detected with both strains. Proteogenomic investigation of
<jats:italic>p</jats:italic>
-cymene- versus succinate-adapted cells of the two strains revealed distinct protein profiles agreeing with the different metabolites formed from
<jats:italic>p</jats:italic>
-cymene. “
<jats:named-content content-type="genus-species">A. aromaticum</jats:named-content>
” pCyN1 specifically produced (i) a putative
<jats:italic>p</jats:italic>
-cymene dehydrogenase (CmdABC) expected to hydroxylate the benzylic methyl group of
<jats:italic>p</jats:italic>
-cymene, (ii) two dehydrogenases putatively oxidizing 4-isopropylbenzyl alcohol (Iod) and 4-isopropylbenzaldehyde (Iad), and (iii) the putative 4-isopropylbenzoate-coenzyme A (CoA) ligase (Ibl). The
<jats:italic>p</jats:italic>
-cymene-specific protein profile of “
<jats:named-content content-type="genus-species">Thauera</jats:named-content>
” sp. pCyN2, on the other hand, encompassed proteins homologous to subunits of toluene-activating benzylsuccinate synthase (termed [4-isopropylbenzyl]succinate synthase IbsABCDEF; identified subunits, IbsAE) and protein homologs of the benzylsuccinate β-oxidation (Bbs) pathway (termed BisABCDEFGH; all identified except for BisEF). This study reveals that two related denitrifying bacteria employ fundamentally different peripheral degradation routes for one and the same substrate,
<jats:italic>p</jats:italic>
-cymene, with the two pathways apparently converging at the level of 4-isopropylbenzoyl-CoA.
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