Comparative genomics of the dairy isolate Streptococcus macedonicus ACA-DC 198 against related members of the Streptococcus bovis/Streptococcus equinus complex

Background: Within the genus Streptococcus, only Streptococcus thermophilus is used as a starter culture in food fermentations. Streptococcus macedonicus though, which belongs to the Streptococcus bovis/Streptococcus equinus complex (SBSEC), is also frequently isolated from fermented foods mainly of dairy origin. Members of the SBSEC have been implicated in human endocarditis and colon cancer. Here we compare the genome sequence of the dairy isolate S. macedonicus ACA-DC 198 to the other SBSEC genomes in order to assess in silico its potential adaptation to milk and its pathogenicity status. Results: Despite the fact that the SBSEC species were found tightly related based on whole genome phylogeny of streptococci, two distinct patterns of evolution were identified among them. Streptococcus macedonicus, Streptococcus infantarius CJ18 and Streptococcus pasteurianus ATCC 43144 seem to have undergone reductive evolution resulting in significantly diminished genome sizes and increased percen...

研究背景：在链球菌属（Streptococcus）中，仅有嗜热链球菌（Streptococcus thermophilus）被用作食品发酵的发酵剂培养物。而隶属于牛链球菌/马链球菌复合群（Streptococcus bovis/Streptococcus equinus complex, SBSEC）的马其顿链球菌（Streptococcus macedonicus），也频繁从以乳制品为主的发酵食品中分离得到。SBSEC的相关菌株已被证实与人类心内膜炎及结肠癌相关。本研究将乳制品分离株马其顿链球菌ACA-DC 198的基因组序列与其他SBSEC菌株的基因组序列进行比对，旨在通过计算机模拟（in silico）评估其对牛乳环境的潜在适应性，以及其致病潜力。

研究结果：尽管基于链球菌全基因组系统发育分析显示SBSEC各物种间亲缘关系紧密，但研究团队在其中发现了两种截然不同的进化模式。马其顿链球菌、婴儿链球菌CJ18以及巴氏链球菌ATCC 43144似乎经历了基因组简化进化，其基因组大小显著缩减，且百分比显著增加。