Studies On The Regulation Of Virulence By PrlP Transcriptional Regulator In Streptococcus Suis Serotype 2

Streptococcus suis serotype 2(SS2)is an important zoonotic pathogen that can cause meningitis,arthritis,sepsis and streptococcal toxic-shock-like syndrome(STSLS).It can cause not only great losses to the pig industry around the world,but also seriously threatens human health.Up to now,the pathogenic mechanism of SS2 has not been fully characterized.In the laboratory,a potential virulence factor PrlP was screened through a transposon mutant library.The analysis revealed that it belongs to the XRE family transcriptional regulatory factors,studying its effect on the virulence of SS2,and systematically analyzing its mechanism to further reveal the mechanism of SS2-caused-diseases is of great significance.To determine the effect of PrlP on SS2 virulence,the prl P gene deletion strain ?prl P and the complementation strain C?prl P were constructed with the SS2 SC19 strain serving as a parent strain.After comparing their biological characteristics,we found that the length of the prl P gene deletion strain ?prl P's chain is significantly longer after vitro culture.The results of the mouse infection experiment showed that,with the deletion of prl P gene,the lethal rate of the infected mice was significantly reduced and the clinical symptoms were significantly alleviated.At the same time,the ability of adhering,inducing the inflammatory factors and causing tissue damage in mice was significantly reduced.After the gene had been replenished,these traits recovered or partially recovered.This indicated that the prl P gene is an important virulence gene of SS2.Due to the structural characteristics of the XRE family of transcriptional regulators that the N-domain(HTH-specific DNA-binding domains)is conservative and the C-domain is highly variable,we further constructed the PrlP key domain that affects SS2 virulence.The N-domain and C-domain deletion mutants(?N(prl P)and ?C(prl P))of the SS2 prl P gene were built and their biological characteristics and pathogenicity in mice were determined.The experimental results showed that the biological characteristics and pathogenicity of the strain ?C(prl P)were not significantly different from those of the wild strain,and the biological characteristics and the pathogenicity of mice of the strain ?N(prl P)is basically the same as the strain ?prl P.After the deletion of the PrlP N-domain,the lethality of the infected mice and the clinical symptoms were significantly reduced.At the same time,the ability of colonization,induction of inflammatory factors,and tissue damage in mice were significantly decreased,and these traits recovered or partially recovered in the strain C?N(prl P).In addition,in vitro phagocytosis experiments showed that SS2's anti-phagocytic ability was decreased after deletion of PrlP or its N-domain.The above results indicate that the N-domain is the major domain in which PrlP regulates SS2 virulence and responds to environmental stress.In order to analyze the mechanism of PrlP regulating the virulence of SS2,the RNAseq was used to analyze PrlP and its N-domain to regulate the expression of SS2 gene.The experimental results show that there are a large number of common differentially expressed genes in the PrlP-deleted strain and its N-domain-deleted strain compared to the wild strain.These include genes associated with many life activities such as nutrient transport and metabolism,cell division,cell wall/membrane/envelope biogenesis,DNA replication recombination and repair,translation,signal transduction mechanisms,and defense mechanisms.Among the above differentially expressed genes,the expression levels of the virulence genes Cia RH,Stk/Stp,ssp A-1,hp1330,fur,etc.were significantly down-regulated;and the expression levels of mre C,mre D,stk and other genes related to cell division were significantly different.It suggests that PrlP or its N-domain may regulate SS2 virulence and cell division by regulating the above genes' expression.In summary,PrlP is an important global transcriptional regulator of Streptococcus suis serotype 2,which can regulate SS2 cell division and other life activities and virulence by regulating SS2 gene expression,and this regulation is mainly caused by its implemented N-domain(HTH specific DNA binding domain).Subsequent further studies using Ch IPseq to identify virulence genes directly or indirectly bound with PrlP will lay the foundation for further analysis of the SS2 virulence regulatory network.