RfeA:a Putative Negative Regulatory Factor Of Pathogenicity Of Streptococcus Suis Type 2

Streptococcus suis is an important swine and zoonotic pathogen, which can cause a variety of diseases, including meningitis, arthritis, endocarditis pneumonia, and sepsis in pigs. In all 33 serotypes(1 to 31,33,and 1/2)described, S. suis serotype 2 (SS2) is the most invasive and prevalent serotype. It is also a zoonotic pathogen for human, which can even cause people’s sudden death by contacting with diseased animals or animal products. S.suis virulence associated factors include muramidase-released protein (MRP), capsular polysaccharide (CPS), extracellular factor (EF), suilysin (SLY) and Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), among which CPS was the only proven critical virulence factor of S. suis. However, knowledge of precise virulence factors and the pathogenesis of the S. suis has not been clearly understood yet. So other virulence associated genes need to be paid attention.A gene belonged to RTX family exoprotein A gene (RfeA), which was reported as pore-forming toxins to tamper with normal host cell processes in some species of bacteria, was only existed in virulent strain of SS2 ZY05719 after comparsion with the avirulent conterparters T15 and epf-like was located in same operon of rfeA. Previous researches showed that RfeA was a secreted protein from SS2 and it could play a role of protective antigen, but the virulence of this gene was not mentioned. Further gene distribution detection among 44 different strians of S. suis showed that it enriched in virulence isolates of SS2 (32/34). Of course, it seems that RfeA may be contribued to the virulence of SS2. To investigate the pathogenic mechanism of rfeA in SS2, an isogenic mutant (△rfeA), as well as the functionally complementation strain (C△rfeA) were constructed. Then the virulence of ArfeA, C△rfeA, and wild strains were evaluated by animal model of zebrafish. To our surprise, compared with the wild counterpart, the virulence of ArfeA appeared significantly enhanced, as well as CArfeA regained relatively low virulence after comprsion with the wild strain.To survey why and how this gene deletion improved the bacterial virulence, some reported putative virulence factor genes, such as mrp, ef, sly, and cps2, as well as epf-like which located in same operon of rfek, were assessed in mRNA level. Interestingly, the transcriptional level of all genes we tested were not significantly different between ArfeA and wild-type strains. Meanwhile, after similarity searched with known regulatory systems, such as stand-alone transcriptional regulators, two-component regulatory systems (TCSs) and eukaryotic-like serine/threonine kinases of SS, rfek. did not belong to any of these. So rfeA might be a novel negative regulatory factor in SS2, or on the other hand, it might affect other negative regulatory factors, but the precise regulatory mechanism was still unknown.