Anaerobic Activation of p-Cymene in Denitrifying Betaproteobacteria: Methyl Group Hydroxylation versus Addition to Fumarate

作者：Strijkstra Annemieke; Trautwein Kathleen; Jarling Rene; Woehlbrand Lars; Doerries Marvin; Reinhardt Richard; Drozdowska Marta; Golding Bernard T; Wilkes Heinz; Rabus Ralf^*

来源：Applied and Environmental Microbiology, 2014, 80(24): 7592-7603.

DOI：10.1128/AEM.02385-14

The betaproteobacteria %26quot;Aromatoleum aromaticum%26quot; pCyN1 and %26quot; Thauera%26quot; sp. strain pCyN2 anaerobically degrade the plant-derived aromatic hydrocarbon p-cymene (4-isopropyltoluene) under nitrate-reducing conditions. Metabolite analysis of p-cymene-adapted %26quot; A. aromaticum%26quot; pCyN1 cells demonstrated the specific formation of 4-isopropylbenzyl alcohol and 4-isopropylbenzaldehyde, whereas with %26quot;Thauera%26quot; 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 p-cymene-versus succinate-adapted cells of the two strains revealed distinct protein profiles agreeing with the different metabolites formed from p-cymene. %26quot; A. aromaticum%26quot; pCyN1 specifically produced (i) a putative p-cymene dehydrogenase (CmdABC) expected to hydroxylate the benzylic methyl group of p-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 p-cymene-specific protein profile of %26quot;Thauera%26quot; 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 beta-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, p-cymene, with the two pathways apparently converging at the level of 4-isopropylbenzoyl-CoA.

• 出版日期2014-12