The CodY regulator is essential for virulence in Streptococcus suis serotype 2.

Liping Feng,Fangyan Yuan,Xiaoping Gao,Xiaofeng Wei,Jiawen Zhu,Cheng Gao,Weicheng Bei,Haitao Chang

doi:10.1038/srep21241

Abstract

The main role of CodY, a global regulatory protein in most low G + C gram-positive bacteria, is in transcriptional repression. To study the functions of CodY in Streptococcus suis serotype 2 (S. suis 2), a mutant codY clone named ∆codY was constructed to explore the phenotypic variation between ∆codY and the wild-type strain. The result showed that the codY mutation significantly inhibited cell growth, adherence and invasion ability of S. suis 2 to HEp-2 cells. The codY mutation led to decreased binding of the pathogen to the host cells, easier clearance by RAW264.7 macrophages and decreased growth ability in fresh blood of Cavia porcellus. The codY mutation also attenuated the virulence of S. suis 2 in BALB/c mice. Morphological analysis revealed that the codY mutation decreased the thickness of the capsule of S. suis 2 and changed the surface structures analylized by SDS-PAGE. Finally, the codY mutation altered the expressions of many virulence related genes, including sialic acid synthesis genes, leading to a decreased sialic acid content in capsule. Overall, mutation of codY modulated bacterial virulence by affecting the growth and colonization of S. suis 2, and at least via regulating sialic acid synthesis and capsule thickness.

Highlights

Control, purified CodY protein expressed by E. coli BL21(DE) from vector pET-28a-codY-His. (e–h) Effect of the codY mutation on the growth of S. suis 2, which was evaluated by OD 600 and CFU counting at indicated time points in Tryptic Soy Broth (TSB) medium with isoleucine (Ile+) (e,f) or in the chemically defined medium (CDM) with (Ile+) or without isoleucine (Ile−) (g,h), respectively
The codY mutation reduced the virulence of S. suis 2 in BALB/c mice and enhanced phagocytosis of S. suis 2 mediated by macrophages
In many low G + C Gram-positive bacteria, CodY is global transcriptional regulator that plays a pivotal role in the regulation of microbial metabolism and virulence[33,34,35,36]

Summary

Introduction

Control, purified CodY protein expressed by E. coli BL21(DE) from vector pET-28a-codY-His. (e–h) Effect of the codY mutation on the growth of S. suis 2, which was evaluated by OD 600 and CFU counting at indicated time points in TSB medium with isoleucine (Ile+) (e,f) or in the chemically defined medium (CDM) with (Ile+) or without isoleucine (Ile−) (g,h), respectively. CodY is a global transcriptional regulator of gene expression in low G + C gram-positive bacteria[16]. Besides regulating genes involved in primary metabolism, CodY regulates the virulence mechanism in various pathogenic gram-positive bacteria[23]. It activates toxin gene expression by regulating the global regulator AtxA in B. anthracis. CodY regulates pel/sagA and mga, loci that themselves positively affect the expression of numerous virulence factors in growth phase-dependent way in Streptococcus pyogenes[27]. We used an in vitro model as reported[1,30] to compare the adhesion ability of Δ codY strain to mammalian cells with that of the wild-type. This study would enhance our understanding of virulence regulation mediated by CodY in S. suis 2

Methods

Results

Conclusion