The CWPS Rubik’s cube: Linking diversity of cell wall polysaccharide structures with the encoded biosynthetic machinery of selected Lactococcus lactis strains

The biosynthetic machinery for cell wall polysaccharide (CWPS) production in lactococci is encoded by a large gene cluster, designatedcwps. This locus displays considerable variation among lactococcal genomes, previously prompting a classification into three distinct genotypes (A-C). In the present study, thecwpsloci of 107 lactococcal strains were compared, revealing the presence of a fourthcwpsgenotype (type D). Lactococcal CWPSs are comprised of two saccharidic structures: a peptidoglycan-embedded rhamnan backbone polymer to which a surface-exposed, poly/oligosaccharidic side-chain is covalently linked. Chemical structures of the side-chain of seven lactococcal strains were elucidated, highlighting their diverse and strain-specific nature. Furthermore, a link betweencwpsgenotype and chemical structure was derived based on the number of glycosyltransferase-encoding genes in thecwpscluster and the presence of conserved genes encoding the presumed priming glycosyltransferase. This facilitates predictions of several structural features of lactococcal CWPSs including (a) whether the CWPS possesses short oligo/polysaccharide side-chains, (b) the number of component monosaccharides in a given CWPS structure, (c) the order of monosaccharide incorporation into the repeating units of the side-chain (for C-type strains), (d) the presence of Galfand phosphodiester bonds in the side-chain, and (e) the presence of glycerol phosphate substituents in the side-chain.