| Résumé | Streptococcus thermophilus strain ST64987 was exposed to a member of a recently discovered group of S. thermophilus phages (the 987 phage group), generating phage‐insensitive mutants, which were then characterized phenotypically and genomically. Decreased phage adsorption was observed in selected bacteriophage‐insensitive mutants, and was partnered with a sedimenting phenotype and increased cell chain length or aggregation. Whole genome sequencing of several bacteriophage‐insensitive mutants identified mutations located in a gene cluster presumed to be responsible for cell wall polysaccharide production in this strain. Analysis of cell surface‐associated glycans by methylation and NMR spectroscopy revealed a complex branched rhamno‐polysaccharide in both ST64987 and phage‐insensitive mutant BIM3. In addition, a second cell wall‐associated polysaccharide of ST64987, composed of hexasaccharide branched repeating units containing galactose and glucose, was absent in the cell wall of mutant BIM3. Genetic complementation of three phage‐resistant mutants was shown to restore the carbohydrate and phage resistance profiles of the wild‐type strain, establishing the role of this gene cluster in cell wall polysaccharide production and phage adsorption and, thus, infection. |
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