The Pentose Moiety of Adenosine and Inosine Is an Important Energy Source for the Fermented-Meat Starter Culture Lactobacillus sakei CTC 494

Abstract

ABSTRACTThe genome sequence ofLactobacillus sakei23K has revealed that the speciesL. sakeiharbors several genes involved in the catabolism of energy sources other than glucose in meat, such as glycerol, arginine, and nucleosides. In this study, a screening of 15L. sakeistrains revealed that arginine, inosine, and adenosine could be used as energy sources by all strains. However, no glycerol catabolism occurred in any of theL. sakeistrains tested. A detailed kinetic analysis of inosine and adenosine catabolism in the presence of arginine byL. sakeiCTC 494, a fermented-meat starter culture, was performed. It showed that nucleoside catabolism occurred as a mixed-acid fermentation in a pH range (pH 5.0 to 6.5) relevant for sausage fermentation. This resulted in the production of a mixture of acetic acid, formic acid, and ethanol from ribose, while the nucleobase (hypoxanthine and adenine in the case of fermentations with inosine and adenosine, respectively) was excreted into the medium stoichiometrically. This indicates that adenosine deaminase activity did not take place. The ratios of the different fermentation end products did not vary with environmental pH, except for the fermentation with inosine at pH 5.0, where lactic acid was produced too. In all cases, no other carbon-containing metabolites were found; carbon dioxide was derived only from arginine catabolism. Arginine was cometabolized in all cases and resulted in the production of both citrulline and ornithine. Based on these results, a pathway for inosine and adenosine catabolism inL. sakeiCTC 494 was presented, whereby both nucleosides are directly converted into their nucleobase and ribose, the latter entering the heterolactate pathway. The present study revealed that the pentose moiety (ribose) of the nucleosides inosine and adenosine is an effective fermentable substrate forL. sakei. Thus, the ability to use these energy sources offers a competitive advantage for this species in a meat environment.