title: Phenotypic and genotypic characterization of peptidoglycan hydrolases of Lactobacillus sakei.
abstract: Lactobacillus sakei, a lactic acid bacterium naturally found in fresh meat and sea products, is considered to be one of the most important bacterial species involved in meat fermentation and bio-preservation. Several enzymes of Lb. sakei species contributing to microbial safeguarding and organoleptic properties of fermented-meat were studied. However, the specific autolytic mechanisms and associated enzymes involved in Lb. sakei are not well understood. The autolytic phenotype of 22 Lb. sakei strains isolated from Tunisian meat and seafood products was evaluated under starvation conditions, at pH 6.5 and 8.5, and in the presence of different carbon sources. A higher autolytic rate was observed when cells were grown in the presence of glucose and incubated at pH 6.5. Almost all strains showed high resistance to mutanolysin, indicating a minor role of muramidases in Lb. sakei cell lysis. Using Micrococcus lysodeikticus cells as a substrate in activity gels zymogram, peptidoglycan hydrolase (PGH) patterns for all strains was characterized by two lytic bands of ∼80 (B1) and ∼70 kDa (B2), except for strain BMG.167 which harbored two activity signals at a lower MW. Lytic activity was retained in high salt and in acid/basic conditions and was active toward cells of Lb. sakei, Listeria monocytogenes, Listeria ivanovii and Listeria innocua. Analysis of five putative PGH genes found in the Lb. sakei 23 K model strain genome, indicated that one gene, lsa1437, could encode a PGH (N-acetylmuramoyl-L-alanine amidase) containing B1 and B2 as isoforms. According to this hypothesis, strain BMG.167 showed an allelic version of lsa1437 gene deleted of one of the five LysM domains, leading to a reduction in the MW of lytic bands and the high autolytic rate of this strain. Characterization of autolytic phenotype of Lb. sakei should expand the knowledge of their role in fermentation processes where they represent the dominant species.
authors: Université Tunis El Manar, Faculté des Sciences de Tunis, LR03ES03 Laboratoire de Microbiologie et Biomolécules Actives, Campus Universitaire, 2092 Tunis, Tunisia.
authors: Afef
authors: A
authors: Najjari
authors: Université Tunis El Manar, Faculté des Sciences de Tunis, LR03ES03 Laboratoire de Microbiologie et Biomolécules Actives, Campus Universitaire, 2092 Tunis, Tunisia.
authors: Houda
authors: H
authors: Amairi
authors: Unité Flore Lactique et Environnement Carné, UR309, INRA, Domaine de Vilvert, F-78350 Jouy en Josas, France.
authors: Stéphane
authors: S
authors: Chaillou
authors: Dipartimento di Scienze e Tecnologie Alimentari e Microbiologiche, Università degli Studi di Milano, Milan, Italy.
authors: Diego
authors: D
authors: Mora
authors: Université Tunis El Manar, Faculté des Sciences de Tunis, LR03ES03 Laboratoire de Microbiologie et Biomolécules Actives, Campus Universitaire, 2092 Tunis, Tunisia.
authors: Abdellatif
authors: A
authors: Boudabous
authors: Unité Flore Lactique et Environnement Carné, UR309, INRA, Domaine de Vilvert, F-78350 Jouy en Josas, France.
authors: Monique
authors: M
authors: Zagorec
authors: Université Tunis El Manar, Faculté des Sciences de Tunis, LR03ES03 Laboratoire de Microbiologie et Biomolécules Actives, Campus Universitaire, 2092 Tunis, Tunisia.
authors: Hadda
authors: H
authors: Ouzari
keywords: Autolysis; Lactobacillus sakei; LysM domains; Mutanolysin; Peptidoglycan hydrolase