Abstract
Lactic acid bacteria (LAB) are Gram positive bacteria widely used in the production of fermented food in particular cheese and yoghurts. Bacteriophage infections during fermentation processes have been for many years a major industrial concern and have stimulated numerous research efforts. Better understanding of the molecular mechanisms of bacteriophage interactions with their host bacteria is required for the development of efficient strategies to fight against infections. The bacterial cell wall plays key roles in these interactions. First, bacteriophages must adsorb at the bacterial surface through specific interactions with receptors that are cell wall components. At next step, phages must overcome the barrier constituted by cell wall peptidoglycan (PG) to inject DNA inside bacterial cell. Also at the end of the infection cycle, phages synthesize endolysins able to hydrolyze PG and lyse bacterial cells to release phage progeny. In the last decade, concomitant development of genomics and structural analysis of cell wall components allowed considerable advances in the knowledge of their structure and function in several model LAB. Here, we describe the present knowledge on the structure of the cell wall glycopolymers of the best characterized LAB emphasizing their structural variations and we present the available data regarding their role in bacteria-phage specific interactions at the different steps of the infection cycle.
Highlights
The cell wall of Gram-positive bacteria which surrounds the cytoplasmic membrane is a complex arrangement of different biopolymers: peptidoglycan (PG), polysaccharides, teichoic acids andproteins (Delcour et al, 1999) (Figure 1A)
We summarize the current knowledge on the different cell wall glycopolymers including polysaccharides, teichoic acids and PG, studied mainly in four model Lactic acid bacteria (LAB) species: Lactococcus lactis, Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus rhamnosus
Further studies will aim at elucidating the inter-strain structural diversity of cell-wall polymers that are phage receptors at the bacterial surface, which could explain the narrow host range of certain L. lactis phages
Summary
The cell wall of Gram-positive bacteria which surrounds the cytoplasmic membrane is a complex arrangement of different biopolymers: peptidoglycan (PG), polysaccharides, teichoic acids and (glyco)proteins (Delcour et al, 1999) (Figure 1A). PG is the major component of the Gram-positive cell wall and it is made of glycan chains cross-linked through short peptide chains It constitutes a network around the bacterial cell on which are linked covalently secondary polymers such as wall teichoic acids (WTA), polysaccharides, or LPXTG-containing proteins. Lactococci and lactobacilli are used as starters in milk fermentations for the production of cheese and yogurts They acidify milk through lactic acid production which limits food spoilage and in addition they contribute to the development of organoleptic properties including texture and flavor (Lortal and Chapot-Chartier, 2005). During the phage infection cycle, the bacterial cell-wall components which possibly show considerable variations between species and strains are key determinants of the specific interactions of bacteriophages with their target bacteria (Samson and Moineau, 2013) (Figure 1A). A growing interest for the structure and function of the cellwall glycopolymers of LAB has emerged in the past years due to their potential involvement in LAB functionality including www.frontiersin.org
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