The capsule (cap) of Streptococcus suis is an anti-phagocytic element and is one of the major virulence factors. However, we have found cap-positive and cap-negative isolates in porcine endocarditis. Here, we compared genome sequences of multiple cap-negative isolates with those of a cap-positive isolate from a single endocarditis. Cap-positive and cap-negative isolates from the same pig were phylogenetically closest compared with those from other pigs. Some of cap-negative isolates from the same pig showed different mutations in capsular polysaccharide synthesis (cps) genes, suggesting that these isolates arisen in pigs after infection. Different mutations in whole-genomes were also found among isolates with identical mutations in cps genes, indicating that mutations in cps genes and the whole-genome occurred independently. Since cap-negative isolates are rarely found in lesions of other diseases, these results suggest that endocarditis lesions may simply favored cap-negative mutants to survive the niches, leading to their persistence in the lesions.

中文翻译：

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从比较基因组学推断猪心内膜炎中荚膜阴性猪链球菌持续存在的基础。

猪链球菌的荚膜（帽）是一种抗吞噬成分，是主要的毒力因子之一。然而，我们在猪心内膜炎中发现了帽阳性和帽阴性分离株。在这里，我们将多个帽阴性分离株的基因组序列与来自单个心内膜炎的帽阳性分离株的基因组序列进行了比较。来自同一头猪的帽阳性和帽阴性分离株与其他猪的分离株在系统发育上最接近。来自同一头猪的一些帽阴性分离株在荚膜多糖合成 (cps) 基因中显示出不同的突变，表明这些分离株是在感染后在猪体内产生的。在 cps 基因突变相同的分离株中也发现了全基因组的不同突变，表明 cps 基因和全基因组的突变是独立发生的。