title: Anaerobic Degradation of p-Alkylated Benzoates and Toluenes.
abstract: The anaerobic degradation of 4-alkylbenzoates and 4-alkyltoluenes is to date a rarely reported microbial capacity. The newly isolated Alphaproteobacterium Magnetospirillum sp. strain pMbN1 represents the first pure culture demonstrated to degrade 4-methylbenzoate completely to CO2 in a process coupled to denitrification. Differential proteogenomic studies in conjunction with targeted metabolite analyses and enzyme activity measurements elucidated a specific 4-methylbenzoyl-coenzyme A (CoA) pathway in this bacterium alongside the classical central benzoyl-CoA pathway. Whilst these two pathways are analogous, in the former the p-methyl group is retained and its 4-methylbenzoyl-CoA reductase (MbrCBAD) is phylogenetically distinct from the archetypical class I benzoyl-CoA reductase (BcrCBAD). Subsequent global regulatory studies on strain pMbN1 grown with binary or ternary substrate mixtures revealed benzoate to repress the anaerobic utilization of 4-methylbenzoate and succinate. The shared nutritional property of betaproteobacterial 'Aromatoleum aromaticum' pCyN1 and Thauera sp. strain pCyN2 is the anaerobic degradation of the plant-derived hydrocarbon p-cymene (4-isopropyltoluene) coupled to denitrification. Notably, the two strains employ two different peripheral pathways for the conversion of p-cymene to 4-isopropylbenzoyl-CoA as the possible first common intermediate. In 'A. aromaticum' pCyN1 a putative p-cymene dehydrogenase (CmdABC) is proposed to hydroxylate the benzylic methyl group, which is subsequently further oxidized to the CoA-thioester. In contrast, Thauera sp. strain pCyN2 employs a reaction sequence analogous to the known anaerobic toluene pathway, involving a distinct branching (4-isopropylbenzyl)succinate synthase (IbsABCDEF).
authors.affiliation: Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University Oldenburg, Oldenburg, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Rabus
authors.forename: Matthias
authors.initials: M
authors.lastname: Boll
authors.forename: Bernard
authors.initials: B
authors.lastname: Golding
authors.forename: Heinz
authors.initials: H
authors.lastname: Wilkes
mesh_terms: D000693:Anaerobiosis; D001421:Bacteria, Anaerobic / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D001565:Benzoates / Q000737:chemistry / Q000378:metabolism*; D001673:Biodegradation, Environmental; D042201:Magnetospirillum / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D014050:Toluene / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001565:Benzoates; D014050:Toluene