Catabolism ofN-Acetylneuraminic Acid, a Fitness Function of the Food-Borne Lactic Acid Bacterium Lactobacillus sakei, Involves Two Newly Characterized Proteins

Abstract

ABSTRACTIn silicoanalysis of the genome sequence of the meat-borne lactic acid bacterium (LAB)Lactobacillus sakei23K has revealed a repertoire of potential functions related to the adaptation of this bacterium to the meat environment. Among these functions, the ability to useN-acetyl-neuraminic acid (NANA) as a carbon source could provide a competitive advantage for growth on meat in which this amino sugar is present. In this work, we proposed to analyze the functionality of a gene cluster encompassingnanTEARandnanK(nanTEAR-nanK). We established that this cluster encoded a pathway allowing transport and early steps of the catabolism of NANA in this genome. We also demonstrated that this cluster was absent from the genome of otherL. sakeistrains that were shown to be unable to grow on NANA. Moreover,L. sakei23KnanA,nanT,nanK, andnanEgenes were able to complementEscherichia colimutants. Construction of different mutants inL. sakei23K ΔnanR, ΔnanT, and ΔnanKand the double mutantL. sakei23K Δ(nanA-nanE) made it possible to show that all were impaired for growth on NANA. In addition, two genes located downstream fromnanK,lsa1644andlsa1645, are involved in the catabolism of sialic acid inL. sakei23K, as aL. sakei23K Δlsa1645mutant was no longer able to grow on NANA. All these results demonstrate that the gene clusternanTEAR-nanK-lsa1644-lsa1645is indeed involved in the use of NANA as an energy source byL. sakei.