Cell Surface of Lactococcus lactis Is Covered by a Protective Polysaccharide Pellicle

Yves F Dufrêne,Guillaume Andre,Michel-Yves Mistou,Saulius Kulakauskas,Elena Bidnenko,Patrick Trieu-Cuot,Christine Péchoux,Pascal Hols,Evgeny Vinogradov,Sylviane Furlan,Irina Sadovskaya,Pascal Courtin,Marie-Pierre Chapot-Chartier

doi:10.1074/jbc.m109.082958

Abstract

In Gram-positive bacteria, the functional role of surface polysaccharides (PS) that are not of capsular nature remains poorly understood. Here, we report the presence of a novel cell wall PS pellicle on the surface of Lactococcus lactis. Spontaneous PS-negative mutants were selected using semi-liquid growth conditions, and all mutations were mapped in a single chromosomal locus coding for PS biosynthesis. PS molecules were shown to be composed of hexasaccharide phosphate repeating units that are distinct from other bacterial PS. Using complementary atomic force and transmission electron microscopy techniques, we showed that the PS layer forms an outer pellicle surrounding the cell. Notably, we found that this cell wall layer confers a protective barrier against host phagocytosis by murine macrophages. Altogether, our results suggest that the PS pellicle could represent a new cell envelope structural component of Gram-positive bacteria.

Highlights

Polysaccharides (PS)5 are omnipresent components of Gram-positive bacteria surfaces, which may be divided into the following three major groups: (i) capsular polysaccharides (CPS), which are in most cases covalently bound to peptidoglycan (PG) and form a thick outer layer, (ii) wall polysaccharides (WPS), which may be attached to the cell wall covalently or not but without forming a capsule, and (iii) extracellular polysac
It was previously established that genes important for the adsorption of phages belonging to this group are located within a 24.2-kb chromosomal gene cluster, which is putatively involved in cell wall polysaccharide (PS) biosynthesis in L. lactis strain IL1403 [5]
We identified a cell wall PS produced by the food bacterium L. lactis that forms a compact pellicle located on the outer surface of the cell

Summary

Introduction

Polysaccharides (PS)5 are omnipresent components of Gram-positive bacteria surfaces, which may be divided into the following three major groups: (i) capsular polysaccharides (CPS), which are in most cases covalently bound to peptidoglycan (PG) and form a thick outer layer, (ii) wall polysaccharides (WPS), which may be attached to the cell wall covalently or not but without forming a capsule, and (iii) extracellular polysac-. The plasmid-encoded genes responsible for EPS production in the dairy strains of L. lactis were characterized, and their organization was found to be similar to that of CPS biosynthesis gene clusters of Gram-positive pathogens [6, 7]. The presence of chromosomally encoded cell surface-associated polysaccharides was suggested for some lactococcal strains [8].

Results

Conclusion