title: Cyclohexane carboxylate and benzoate formation from crotonate in Syntrophus aciditrophicus.
abstract: The anaerobic, syntrophic bacterium Syntrophus aciditrophicus grown in pure culture produced 1.4 +/- 0.24 mol of acetate and 0.16 +/- 0.02 mol of cyclohexane carboxylate per mole of crotonate metabolized. [U-13C]crotonate was metabolized to [1,2-(13)C]acetate and [1,2,3,4,5,7-(13)C]cyclohexane carboxylate. Cultures grown with unlabeled crotonate and [13C]sodium bicarbonate formed [6-(13)C]cyclohexane carboxylate. Trimethylsilyl (TMS) derivatives of cyclohexane carboxylate, cyclohex-1-ene carboxylate, benzoate, pimelate, glutarate, 3-hydroxybutyrate, and acetoacetate were detected as intermediates by comparison of retention times and mass spectral profiles to authentic standards. With [U-(13)C]crotonate, the m/z-15 ion of TMS-derivatized glutarate, 3-hydroxybutyrate, and acetoacetate each increased by +4 mass units, and the m/z-15 ion of TMS-derivatized pimelate, cyclohex-1-ene carboxylate, benzoate, and cyclohexane carboxylate each increased by +6 mass units. With [13C]sodium bicarbonate and unlabeled crotonate, the m/z-15 ion of TMS derivatives of glutarate, pimelate, cyclohex-1-ene carboxylate, benzoate, and cyclohexane carboxylate each increased by +1 mass unit, suggesting that carboxylation occurred after the synthesis of a four-carbon intermediate. With [1,2-(13)C]acetate and unlabeled crotonate, the m/z-15 ion of TMS-derivatized 3-hydroxybutyrate, acetoacetate, and glutarate each increased by +0, +2, and +4 mass units, respectively, and the m/z-15 ion of TMS-derivatized pimelate, cyclohex-1-ene carboxylate, benzoate, cyclohexane carboxylate, and 2-hydroxycyclohexane carboxylate each increased by +0, +2, +4, and +6 mass units. The data are consistent with a pathway for cyclohexane carboxylate formation involving the condensation of two-carbon units derived from crotonate degradation with CO2 addition, rather than the use of the intact four-carbon skeleton of crotonate.
authors.affiliation: Department of Botany and Microbiology, University of Oklahoma, 770 Van Vleet Oval, Norman, OK 73019, USA.
authors.forename: Housna
authors.initials: H
authors.lastname: Mouttaki
authors.forename: Mark A
authors.initials: MA
authors.lastname: Nanny
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McInerney
mesh_terms: D001565:Benzoates / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism; D003437:Crotonates / Q000378:metabolism*; D003470:Culture Media; D003509:Cyclohexanecarboxylic Acids / Q000737:chemistry / Q000378:metabolism*; D020564:Deltaproteobacteria / Q000254:growth & development / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction
chemical_list: D001565:Benzoates; D002247:Carbon Isotopes; D003437:Crotonates; D003470:Culture Media; D003509:Cyclohexanecarboxylic Acids