Delorme Christine, Abraham Anne-Laure, Renault Pierre, Guédon Eric
INRA, UMR 1319 Micalis, Domaine de Vilvert, F-78352 Jouy-en-Josas, France; AgroParisTech, UMR MICALIS, Jouy-en-Josas, France.
INRA, UMR 1319 Micalis, Domaine de Vilvert, F-78352 Jouy-en-Josas, France; AgroParisTech, UMR MICALIS, Jouy-en-Josas, France.
Infect Genet Evol. 2015 Jul;33:381-92. doi: 10.1016/j.meegid.2014.10.001. Epub 2014 Oct 13.
The salivarius group of streptococci is of particular importance for humans. This group consists of three genetically similar species, Streptococcus salivarius, Streptococcus vestibularis and Streptococcus thermophilus. S. salivarius and S. vestibularis are commensal organisms that may occasionally cause opportunistic infections in humans, whereas S. thermophilus is a food bacterium widely used in dairy production. We developed Multilocus sequence typing (MLST) and comparative genomic analysis to confirm the clear separation of these three species. These analyses also identified a subgroup of four strains, with a core genome diverging by about 10%, in terms of its nucleotide sequence, from that of S. salivarius sensu stricto. S. thermophilus species displays a low level of nucleotide variability, due to its recent emergence with the development of agriculture. By contrast, nucleotide variability is high in the other two species of the salivarius group, reflecting their long-standing association with humans. The species of the salivarius group have genome sizes ranging from the smallest (∼ 1.7 Mb for S. thermophilus) to the largest (∼ 2.3 Mb for S. salivarius) among streptococci, reflecting genome reduction linked to a narrow, nutritionally rich environment for S. thermophilus, and natural, more competitive niches for the other two species. Analyses of genomic content have indicated that the core genes of S. salivarius account for about two thirds of the genome, indicating considerable variability of gene content and differences in potential adaptive features. Furthermore, we showed that the genome of this species is exceptionally rich in genes encoding surface factors, glycosyltransferases and response regulators. Evidence of widespread genetic exchanges was obtained, probably involving a natural competence system and the presence of diverse mobile elements. However, although the S. salivarius strains studied were isolated from several human body-related sites (all levels of the digestive tract, skin, breast milk, and body fluids) and included clinical strains, no genetic or genomic niche-specific features could be identified to discriminate specific group.
唾液链球菌群对人类尤为重要。该菌群由三个基因相似的物种组成，即唾液链球菌、前庭链球菌和嗜热链球菌。唾液链球菌和前庭链球菌是共生生物，偶尔可能会在人类中引起机会性感染，而嗜热链球菌是一种广泛用于乳制品生产的食用细菌。我们开发了多位点序列分型（MLST）和比较基因组分析，以确认这三个物种的明确区分。这些分析还鉴定出一个由四个菌株组成的亚群，其核心基因组在核苷酸序列上与狭义的唾液链球菌的核心基因组相差约10%。由于嗜热链球菌是随着农业发展而新近出现的，其核苷酸变异性较低。相比之下，唾液链球菌群的其他两个物种的核苷酸变异性较高，这反映了它们与人类的长期关联。在链球菌中，唾液链球菌群各物种的基因组大小从最小的（嗜热链球菌约1.7 Mb）到最大的（唾液链球菌约2.3 Mb）不等，这反映出嗜热链球菌因所处营养丰富的狭窄环境而导致基因组缩减，而其他两个物种则处于自然的、竞争更激烈的生态位。基因组内容分析表明，唾液链球菌的核心基因约占基因组的三分之二，这表明基因内容存在相当大的变异性以及潜在适应性特征的差异。此外，我们还表明，该物种的基因组在编码表面因子、糖基转移酶和应答调节因子的基因方面异常丰富。我们获得了广泛基因交换的证据，可能涉及自然感受态系统和多种移动元件的存在。然而，尽管所研究的唾液链球菌菌株是从多个与人体相关的部位（消化道各部位、皮肤、母乳和体液）分离得到的，并且包括临床菌株，但未发现可区分特定群体的遗传或基因组生态位特异性特征。
