Dr. Jekyll or Mr. Hyde? The duality of Streptococcus sanguinis as friend and foe.

摘要血链球菌是口腔菌群中数量最多的一种，是一种很有前途的口腔致病菌 益生菌，因为它已经与人类的口腔健康有关，并显示出与口腔病原体竞争。 相反，S.血吸虫也是细菌性心内膜炎的重要原因，这是一种严重的心脏感染 在美国，每年有超过40，000人受到影响，死亡率超过20%。心内膜炎是 美国牙医的严重关切，他们通常在侵入性治疗之前为高危患者提供抗生素预防。 牙科手术。S. sanguinis的生活方式作为一个健康相关的 对细菌或严重的病原体知之甚少。S.血统因素， 重要的口腔健康与心内膜炎的毒力将有助于发展有效和安全的 益生菌和更有针对性的抗心内膜炎药物在牙科手术。一个重大障碍 该领域的进展是缺乏遗传学、表观遗传学或表型特征的分离物。 许多研究采用了各种特征不佳的菌株，其中许多不再是 分类为S.这使得很难评估调查结果。此外，相关的链球菌属物种是 众所周知的遗传多样性，和其他表观遗传机制已被证明是驱动 表型多样性和毒性，甚至在克隆种群。尽管SK36的完整基因组 尽管已经发表，但其表观遗传特征（即甲基化组）是未知的，并且无论如何，没有单一菌株可以捕获 物种的真正能力。这项提议将首先利用单分子 实时（SMRT）测序以产生40个真正的S.血吸虫菌株， 代表口腔和心内膜炎分离株。这将揭示核心和附属基因组相关， 口腔和心内膜炎的环境小生境，除了每个分离物的甲基化组。中央 这一建议的假设是，双重生活方式的S。A）通过存在或 缺乏特定的遗传基因座（即毒力基因、毒力岛或质粒）或B）表观遗传编码， 由允许的环境小生境内的转录组学改变诱导。体内心内膜炎模型 将用于筛选感染性心内膜炎毒力，并测试是否有针对性的重组等基因 突变体缺乏毒力，使它们成为开发为口服益生菌的合适候选者。的 直接结果是S。sanguinis菌株收集，其在遗传学上、表观遗传学上和 表型定义，并将提供给研究界，并确定 无论是S.血吸虫心内膜炎毒力是遗传或表观遗传编码的。长期结果 将是创造出具有低心内膜炎毒力的菌株。如果毒力得到控制 表观遗传学上S.由于它是在一些最接近的亲属，心内膜炎毒力的损失将是 伴随着口服竞争力的增加，使这些菌株成为口服益生菌开发的理想选择。

ABSTRACT Streptococcus sanguinis is an abundant member of the oral microbiota and a promising oral probiotic since it has been associated with oral health in humans and shown to compete with oral pathogens. Conversely, S. sanguinis is also an important cause of bacterial endocarditis, a serious infection of the heart that affects >40,000 people in the U.S each year and has mortality rates exceeding 20%. Endocarditis is of critical concern to U.S dentists, who typically provide antibiotic prophylaxis to high-risk patients prior to invasive dental procedures. The underlying cause of the duality in S. sanguinis lifestyle as a health-associated commensal or a serious pathogen is poorly understood. Delineation of the S. sanguinis factors that are important for oral health versus endocarditis virulence would facilitate the development of efficacious and safe probiotics, and more targeted prophylactics against endocarditis during dental procedures. A significant barrier to progress in the field is the paucity of genetically-, epigenetically-, or phenotypically- characterized isolates. Numerous studies have employed a variety of poorly characterized strains, many of which are no longer classified as S. sanguinis, making it difficult to assess findings. Moreover, related Streptococcus species are notoriously genetically diverse, and additional epigenetic mechanisms have been demonstrated to drive phenotypic diversity and virulence even within clonal populations. Although the complete genome of SK36 has been published, its epigenetic profile (i.e. methylome) is unknown and, regardless, no single strain can capture the true capabilities of the species. This proposal will surmount these barriers by first using single-molecule real-time (SMRT) sequencing to generate complete genomes/epigenomes of 40 bona fide S. sanguinis strains, representing both oral and endocarditis isolates. This will reveal the core and accessory genomes related to oral and endocarditis environmental niches, in addition to the methylome of each isolate. The central hypothesis of this proposal is that the dual lifestyle of S. sanguinis is either A) facilitated by the presence or absence of specific genetic loci (i.e. virulence genes, islands, or plasmids) or B) epigenetically encoded and induced by transcriptomic alterations within permissive environmental niches. An in-vivo endocarditis model will be used to screen for infective endocarditis virulence and test whether targeted reengineered isogenic mutants are deficient for virulence, making them suitable candidates for development as oral probiotics. The immediate outcomes will be an S. sanguinis strain collection that is genetically-, epigenetically-, and phenotypically defined and which will be made available to the research community, and the ascertainment of whether S. sanguinis endocarditis virulence is genetically or epigenetically encoded. The long-term outcome will be the creation of strains engineered to have low endocarditis virulence. If virulence is controlled epigenetically in S. sanguinis as it is in some of its closest relatives, the loss of endocarditis virulence will be accompanied by an increase in oral competitiveness, making these strains ideal for oral probiotic development.