A Novel Pathway of Aerobic Benzoate Catabolism in the Bacteria Azoarcus evansii and Bacillus stearothermophilus

Abstract

The aerobic catabolism of benzoate was studied in the Gram-negative proteobacterium Azoarcus evansii and in the Gram-positive bacterium Bacillus stearothermophilus. In contrast to earlier proposals, benzoate was not converted into hydroxybenzoate or gentisate. Rather, benzoyl-CoA was a product of benzoate catabolism in both microbial species under aerobic conditions in vivo. Benzoyl-CoA was converted into various CoA thioesters by cell extracts of both species in oxygen- and NADPH-dependent reactions. Using [ring- 13C6]benzoyl-CoA as substrate, cis-3,4-[2,3,4,5,6- 13C5]dehydroadipyl-CoA, trans-2,3-[2,3,4,5,6- 13C5] dehydroadipyl-CoA, the 3,6-lactone of 3-[2,3,4,5,6-13C5]hydroxyadipyl-CoA and 3-[2,3, 4,5,6-13C5]hydroxyadipyl-CoA were identified as products by NMR spectroscopy. A protein mixture of A. evansii transformed [ring- 13C6]benzoyl-CoA in an NADPH- and oxygen-dependent reaction into 6-[2,3,4,5,6-13C5]hydroxy-3-hexenoyl-CoA. The data suggest a novel aerobic pathway of benzoate catabolism via CoA intermediates leading to β-ketoadipyl-CoA, an intermediate of the known β-ketoadipate pathway.