Parasites & Microbes, Wellcome Sanger Institute, Hinxton, UK.
Department of Genetics, University of Cambridge, Cambridge, UK.
Microb Genom. 2022 Feb;8(2). doi: 10.1099/mgen.0.000753.
Mitis group are human obligate bacteria residing in the nasopharynx and oral cavity. They comprise both commensal and pathogenic species with the most well-known being a leading cause of meningitis and pneumonia. A primary difference between the commensal and pathogenic species is the presence of the polysaccharide capsule - a major virulence factor in , also present in other commensal species. Our current understanding of the evolutionary divergence of the pathogenic and commensal species has been inferred from extant strains. Ancient genomes can further elucidate streptococcal evolutionary history. We extracted streptococcal genome reads from a 5700-year-old ancient metagenome and worked towards characterizing them. Due to excessive within- and between-species recombination common among streptococci we were unable to parse individual species. Further, the composite reads of the ancient metagenome do not fit within the diversity of any specific extant species. Using a capsular gene database and AT-content analysis we determined that this ancient metagenome is missing polysaccharide synthesis genes integral to streptococcal capsule formation. The presence of multiple zinc metalloproteases suggests that adaptation to host IgA1 had begun and the presence of other virulence factors further implies development of close host-microbe interactions, though the absence of a capsule suggests an inability to cause invasive disease. The presence of specific virulence factors such as pneumolysin implies stable maintenance of such genes through streptococcal evolution that may strengthen their value as anti-pneumococcal vaccine antigens, while maintaining awareness of their potential presence in commensal species. Following from Jensen 's initial analysis we provide historical context for this long time human nasopharyngeal resident, the Mitis group .
米蒂斯组是人类鼻咽和口腔的专性细菌。它们包括共生和致病物种，其中最著名的是导致脑膜炎和肺炎的主要原因。共生和致病物种之间的一个主要区别是存在多糖荚膜——在 中也是一种主要的毒力因子，也存在于其他共生物种中。我们对致病性和共生性物种进化分歧的理解是根据现存菌株推断出来的。古代基因组可以进一步阐明链球菌的进化历史。我们从一个 5700 年前的古代宏基因组中提取了链球菌基因组读数，并努力对其进行特征描述。由于链球菌中普遍存在的种内和种间重组，我们无法解析单个物种。此外，古代宏基因组的复合读数不符合任何特定现存物种的多样性。使用荚膜基因数据库和 AT 含量分析，我们确定这个古代宏基因组缺少形成链球菌荚膜所必需的多糖合成基因。多种锌金属蛋白酶的存在表明，对宿主 IgA1 的适应已经开始，其他毒力因子的存在进一步意味着宿主与微生物之间的密切相互作用的发展，尽管缺乏荚膜表明其无法引起侵袭性疾病。肺炎球菌溶血素等特定毒力因子的存在意味着这些基因在链球菌进化过程中得到了稳定的维持，这可能增强了它们作为抗肺炎球菌疫苗抗原的价值，同时也需要意识到它们在共生物种中的潜在存在。继 Jensen 的初步分析之后，我们为这个在人类鼻咽长期存在的米蒂斯组提供了历史背景。
