NOVEL ASPECTS OF BENZOATE AND CROTONATE METABOLISM

In anoxic environments, many aromatic compounds (AC)are transformed to benzoylCoA, prior todearomatization and ring cleavage. Due to theresonance stability of the aromatic ring, AC aredifficult to degrade in the absence of O2. Benzoatedegradation in methanogenic ecosystems is mediated bysyntrophic association of a fermentative bacteriumwith a H2/formate-using methanogen. The metabolism ofcrotonate in the strictly anaerobic bacteriaS.aciditrophicus (SB) was studied andindicated that cyclohexane carboxylate and acetate asend products. In addition to benzoate fermentation,SB as the ability to use benzoate as an electronacceptor with crotonate as the electrondonor.Phototrophic and denitrifying bacteria couplethe hydrolysis of 2 ATP to reduce benzoylCoA tocyclohexediene carboxylCoA. The use ofsuch an energy intensive reaction by fermentativebacteria such as SB has been questioned since it isnot clear how net ATP synthesis would occur. Theutilization of fluorobenzoate by SB allowed thedetection of a fluorinated diene intermediate.Proteomic analysis of SB grown with crotonate orbenzoate allowed the identification of geneproducts involved in benzoate metabolism.