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Background  Bacterial cell surface-associated polysaccharides are involved in the interactions of bacteria with their environment and play an important role in the communication between pathogenic bacteria and their host organisms. Cell surface polysaccharides of probiotic species are far less well described. Therefore, improved knowledge on these molecules is potentially of great importance to understand the strain-specific and proposed beneficial modes of probiotic action.    Results  The  Lactobacillus plantarum  WCFS1 genome encodes 4 clusters of genes that are associated with surface polysaccharide production. Two of these clusters appear to encode all functions required for capsular polysaccharide formation ( cps2A-J  and  cps4A-J ), while the remaining clusters are predicted to lack genes encoding chain-length control functions and a priming glycosyl-transferase ( cps1A-I  and  cps3A-J ). We constructed  L. plantarum  WCFS1 gene deletion mutants that lack individual (Δ cps1A-I ,  Δcps2A-J , Δ cps3A-J  and Δ cps4A-J ) or combinations of  cps  clusters (Δ cps1A-3J  and Δ cps1A-3I , Δ cps4A-J ) and assessed the genome wide impact of these mutations by transcriptome analysis. The  cps  cluster deletions influenced the expression of variable gene sets in the individual  cps  cluster mutants, but also considerable numbers of up- and down-regulated genes were shared between mutants in  cps  cluster 1 and 2, as well as between mutant in  cps  clusters 3 and 4. Additionally, the composition of overall cell surface polysaccharide fractions was altered in each mutant strain, implying that despite the apparent incompleteness of  cps1A-I  and  cps3A-J , all clusters are active and functional in  L. plantarum . The Δ cps1A-I  strain produced surface polysaccharides in equal amounts as compared to the wild-type strain, while the polysaccharides were characterized by a reduced molar mass and the lack of rhamnose. The mutants that lacked functional copies of  cps2A-J ,  cps3A-J  or  cps4A-J  produced decreased levels of surface polysaccharides, whereas the molar mass and the composition of polysaccharides was not affected by these cluster mutations. In the quadruple mutant, the amount of surface polysaccharides was strongly reduced. The impact of the  cps  cluster mutations on toll-like receptor (TLR)-mediated human nuclear factor (NF)-κB activation in host cells was evaluated using a TLR2 reporter cell line. In comparison to a  L. plantarum  wild-type derivative, TLR2 activation remained unaffected by the Δ cps1A-I  and Δ cps3A-J  mutants but appeared slightly increased after stimulation with the Δ cps2A-J  and Δ cps4A-J  mutants, while the Δ cps1A-3J  and Δ cps1A-3J,  Δ cps4A-J  mutants elicited the strongest responses and clearly displayed enhanced TLR2 signaling.    Conclusions  Our study reveals that modulation of surface glycan characteristics in  L. plantarum  highlights the role of these molecules in shielding of cell envelope embedded host receptor ligands. Although the apparently complete  cps  clusters ( cps2A-J  and  cps4A-J ) contributed individually to this shielding, the removal of all  cps  clusters led to the strongest signaling enhancement. Our findings provide new insights into cell surface glycan biosynthesis in  L. plantarum , which bears relevance in the context of host-cell signaling by probiotic bacteria.

Impact of 4 Lactobacillus plantarum capsular polysaccharide clusters on surface glycan composition and host cell signaling