Identification of beta-oxidation and thioesterase activities in Staphylococcus carnosus 833 strain

Staphylococcus carnosus 833, inoculated into sausage meat, increased the level of methyl ketones, which contributed to the cured aroma. These ketones can arise from incomplete beta-oxidation followed by two enzymatic activities: a thioesterase and a decarboxylase. In this study we identified the beta-oxidative pathway (through the measure of 3-hydroxyacyl-CoA dehydrogenase activity) and the thioesterase activity in extracts of S. carnosus cells grown in the presence of different methyl esters. The beta-oxidative system was induced by methyl esters and highest induction was found with a 12-carbon substrate. It was specific for medium chain length fatty acyl CoA substrates. Its maximal activity was observed at the end of stationary growth phase. HPLC analyses of acyl-CoA after incubation of cell extracts with palmitoyl-CoA showed that the beta-oxidation system released preferentially long chain hydroxyacyl-CoAs, enoyl-CoAs, and acyl-CoAs. The time-course of intermediate formation indicated a precursor product relationship indicative of a model of free intermediates which could be further deacylated by a thioesterase. The thioesterase activity was enhanced when S. carnosus was grown in the presence of methyl esters with at least 12 carbons and this enzyme was specific for short chain acyl-CoAs. The maximal activity was reached at the stationary growth phase.