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

Staphylococcus carnosus 833, inoculated into sausage meat. increased the le vel of methyl ketones, which contributed to the cured aroma. These ketones call arise from incomplete beta-oxidation followed by two enzymatic activit ies: a thioesterase and a decarboxylase. In this study we identified the be ta-oxidative pathway (through the measure of 3-hydroxyacyl-CoA dehydrogenas e 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-car bon substrate. It was specific for medium chain length fatty acyl CoA subst rates. Its maximal activity was observed at the end of stationary growth ph ase. HPLC analyses of acyl-CoA after incubation of cell extracts with palmi toyl-CoA showed that the beta-oxidation system released preferentially long chain hydroxyacyl-CoAs, enoyl-CoAs, and acyl-CoAs. The timecourse of inter mediate formation indicated a precursor-product relationship indicative of a model of free intermediates which could be further deacylated by a thioes terase. The thioesterase activity was enhanced when S. carnosus was grown i n the presence of methyl esters with at least 12 carbons and this enzyme wa s specific for short chain acyl-CoAs. The maximal activity was reached at t he stationary growth phase. (C) 2000 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies.