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

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.

Recognition of Gram-positive Intestinal Bacteria by Hybridoma- and Colostrum-derived Secretory Immunoglobulin A Is Mediated by Carbohydrates

“…Lactobacillus lactis harbors a particular, thick outer layer composed of polysaccharides acting as a protective capsule (45). This polysaccharide envelope conferring to the bacterium a protective barrier against phagocytosis by murine macrophages appears to be restricted to Gram-positive bacteria and might as well serve as a particular constituent involved in recognition by SIgA or SC.…”

Structure and Molecular Assignment of Lactococcal Phage TP901-1 Baseplate

“…Image processing was performed using the IMAGIC V software (25). Single-molecule images (18,841) were extracted semiautomatically from raw micrographs using Boxer (26) and corrected for the phase contrast-transfer function (CTF) by phase flipping. Some preferential views were selected by visual inspection and chosen as references using the multireference alignment module of the IMAGIC V software (25).…”

“…Combining these results with the EM reconstruction of the "tripod" formed by the TP901-1 BppU-BppL complex, we assigned the positions of four different BP components (BppU, BppL, Dit, and Tal) in the EM maps. Six tripods were fitted into the wild-type BP EM map at its periphery, highlighting its hexagonal symmetry and providing 54 binding sites available for anchoring the phage to its host through phosphosugar receptors (18). This high number of binding sites results in a very large avidity effect, as illustrated by SPR (BIAcore) measurements on a model system consisting of tripod/DARPin (designed ankyrin repeat protein) interactions.…”

Crystal Structure of Bacteriophage SPP1 Distal Tail Protein (gp19.1)

“…This correlates with a different strategy of adsorption to the host bacterium. P335 and 936 members recognize cell-wall saccharides, putatively lipoteichoic acids (41)(42)(43)(44), or a new type of phosphosaccharide (45). SPP1 (and the lactococcal phage c2 (46)) binds reversibly to saccharides in a first specific step and then interacts irreversibly with the membrane protein YueB (47,48).…”