Complete Genome and Transcriptomes of Streptococcus parasanguinis FW213: Phylogenic Relations and Potential Virulence Mechanisms

Streptococcus parasanguinis, a primary colonizer of the tooth surface, is also an opportunistic pathogen for subacute endocarditis. The complete genome of strain FW213 was determined using the traditional shotgun sequencing approach and further refined by the transcriptomes of cells in early exponential and early stationary growth phases in this study. The transcriptomes also discovered 10 transcripts encoding known hypothetical proteins, one pseudogene, five transcripts matched to the Rfam and additional 87 putative small RNAs within the intergenic regions defined by the GLIMMER analysis. The genome contains five acquired genomic islands (GIs) encoding proteins which potentially contribute to the overall pathogenic capacity and fitness of this microbe. The differential expression of the GIs and various open reading frames outside the GIs at the two growth phases suggested that FW213 possess a range of mechanisms to avoid host immune clearance, to colonize host tissues, to survive within oral biofilms and to overcome various environmental insults. Furthermore, the comparative genome analysis of five S. parasanguinis strains indicates that albeit S. parasanguinis strains are highly conserved, variations in the genome content exist. These variations may reflect differences in pathogenic potential between the strains.副血链球菌（Streptococcus parasanguinis）是牙齿表面的初级定植菌，同时也是引发亚急性心内膜炎的机会致病菌。本研究采用传统鸟枪法测序（shotgun sequencing）技术解析了FW213菌株的完整基因组，并结合指数生长早期与稳定生长早期的细胞转录组（transcriptome）数据对基因组进行了进一步优化。通过转录组分析，本研究共发现10个编码已知假设蛋白（hypothetical proteins）的转录本、1个假基因（pseudogene），以及5个与Rfam数据库匹配的转录本；同时在GLIMMER分析划定的基因间区（intergenic regions）内，鉴定出87个潜在小RNA。该基因组包含5个获得性基因组岛（genomic islands, GIs），其编码的蛋白可能有助于提升该菌株的整体致病能力与环境适应性。两种生长阶段下，基因组岛及基因组岛外各类开放阅读框（open reading frames）的差异表达表明，FW213具备多种应对宿主免疫清除、定植宿主组织、在口腔生物膜中存活以及抵御各类环境胁迫的机制。此外，对5株副血链球菌的比较基因组分析（comparative genome analysis）显示，尽管副血链球菌菌株间基因组保守性较高，但仍存在基因组内容的差异。这些差异或可反映不同菌株间致病潜力的区别。