Streptococcus Suis Serotype 9 Passaged In Mice And Streptococcus Suis Comparative Genomic Research

A strain of Streptococcus suis serotype 9 (ND13 strain) isolated from infected pig was 2, 000 times higher of the lethal dose of mouse after being passaged 55 times and became adapted in mice. Differences of completely gene, sequenced by next generation and three generations sequencing technology, were found between SS9-p0 and mice-adapted strains.The complete genome is 2,142,184 nt in length, including 2,091 ORFs,56t RNA and 37 non-coding RNA. The coding gene was aligned using online alignment program (BLAST) followed by functional annotation in KEGG, GO, COG database. Five mainly virulence factors were found through searching VFDB database, which three of them (hasC, glf, CpsB/Cps4B) related to synthesis of capsular polysaccharide, Fbp/pavA related with transport across the blood brain barrier and clpP related to living intracellular.Analyzation of Pan-genome and core-genome phylogenetic relationship of 23 complete genome of Streptococcus suis (22 from Genbank and SS9-p0) shows that genome of Streptococcus suis is an open Pan-genome.Sites number of SNPs, insertion, deletion, copy number variation, and structure sariation were 9,10,17,4 and 717 in the genome of mice-adapted isolate (SS9-p55). Seven gene related to the virulence were found in the code gene and insertion-deletion mutant gene. Analyzation of these results indicate that a 36bp insertion in the LigA gene, respond to the replication, increase the propagation of SS9 in mouse; the decrease of copy number of a 500bp repeating nucleotides from collagen-binding adhesion gene increase the adhesion to host cell; mutation of single nucleotides in Sap heighten the transmission of blood-brain barrier and 4 gene code for receptor and enzyme of ABC transmission system.We screened a SS-9 strain, mice adapted and virulence enhanced, through passage in the mice by simulating the bacterial-host interaction process. The methods we used give a new insight to investigate the phylogenetic of bacterial. Besides that, precious information was available to study the virulence increasing in the processing of bacterial-host interaction.