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.

中文翻译：

---

细胞壁相关的多糖是噬菌体吸附到嗜热链球菌细胞表面所必需的。

嗜热链球菌菌株ST64987暴露于最近发现的嗜热链球菌组中的成员噬菌体（987个噬菌体组），产生对噬菌体不敏感的突变体，然后对其进行表型和基因组表征。在某些对噬菌体不敏感的突变体中观察到噬菌体吸附减少，并与沉降表型和增加的细胞链长度或聚集相伴。几个对噬菌体不敏感的突变体的全基因组测序确定了位于基因簇中的突变，这些突变可能与该菌株的细胞壁多糖产生有关。通过甲基化和NMR光谱分析细胞表面相关的聚糖，发现ST64987和噬菌体不敏感突变体BIM3中都存在复杂的分支鼠李糖多糖。此外，第二个与细胞壁相关的多糖ST64987，由含有半乳糖和葡萄糖的六糖分支重复单元组成，在突变体BIM3的细胞壁中不存在。证明了三个噬菌体抗性突变体的遗传互补可恢复野生型菌株的碳水化合物和噬菌体抗性谱，从而确立了该基因簇在细胞壁多糖产生，噬菌体吸附以及感染中的作用。