A cell wall-associated polysaccharide is required for bacteriophage adsorption to the Streptococcus thermophilus cell surface.

Molecular microbiology 2020 Jul

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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. © 2020 John Wiley & Sons Ltd.

Citation

Brian McDonnell, Laurens Hanemaaijer, Francesca Bottacini, Philip Kelleher, Katherine Lavelle, Irina Sadovskaya, Evgeny Vinogradov, Emiel Ver Loren van Themaat, Thijs Kouwen, Jennifer Mahony, Douwe van Sinderen. A cell wall-associated polysaccharide is required for bacteriophage adsorption to the Streptococcus thermophilus cell surface. Molecular microbiology. 2020 Jul;114(1):31-45