Anaerobic degradation of n-hexane in a denitrifying bacterium: further degradation of the initial intermediate (1-methylpentyl)succinate via C-skeleton rearrangement.
The anaerobic degradation pathway of the saturated hydrocarbon n-hexane in a denitrifying strain (HxN1) was examined by gas chromatography-mass spectrometry of derivatized extracts from cultures grown with unlabeled and deuterated substrate; several authentic standard compounds were included for comparison. The study was focused on possible reaction steps that follow the initial formation of (1-methylpentyl)succinate from n-hexane and fumarate. 4-Methyloctanoic, 4-methyloct-2-enoic, 2-methylhexanoic, 2-methylhex-2-enoic and 3-hydroxy-2-methylhexanoic acids (in addition to a few other methyl-branched acids) were detected in n-hexane-grown but not in n-hexanoate-grown cultures. Labeling indicated preservation of the original carbon chain of n-hexane in these acids. Tracing of the deuterium label of 3- d1-(1-methylpentyl)succinate in tentative subsequent products indicated a deuterium/carboxyl carbon exchange in the succinate moiety. This suggests that the metabolism of (1-methylpentyl)succinate employs reactions analogous to those in the established conversion of succinyl-CoA via methylmalonyl-CoA to propionyl-CoA. Accordingly, a pathway is proposed in which (1-methylpentyl)succinate is converted to the CoA-thioester, rearranged to (2-methylhexyl)malonyl-CoA and decarboxylated (perhaps by a transcarboxylase) to 4-methyloctanoyl-CoA. The other identified fatty acids match with a further degradation of 4-methyloctanoyl-CoA via rounds of conventional beta-oxidation. Such a pathway would also allow regeneration of fumarate (for n-hexane activation) from propionyl-CoA formed as intermediate and hence present a cyclic process.
Wilkes
Heinz
H
Institut für Erdöl und Organische Geochemie, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany. wilkes@gfz-potsdam.de
Rabus
Ralf
R
Fischer
Thomas
T
Armstroff
Antje
A
Behrends
Astrid
A
Widdel
Friedrich
F
D000473:Alkanes / Q000032:analysis / Q000378:metabolism*; D000693:Anaerobiosis; D001419:Bacteria / Q000254:growth & development / Q000378:metabolism*; D002208:Caproates / Q000378:metabolism; D003470:Culture Media; D003903:Deuterium; D005650:Fumarates / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D006586:Hexanes / Q000737:chemistry / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D010084:Oxidation-Reduction; D013386:Succinates / Q000032:analysis / Q000378:metabolism*
C422203:(1-methylpentyl)succinate; D000473:Alkanes; D002208:Caproates; D003470:Culture Media; D005650:Fumarates; D006586:Hexanes; D009566:Nitrates; D013386:Succinates; C037652:hexanoic acid; C026385:n-hexane; C032005:fumaric acid; D003903:Deuterium