A functional peptidoglycan hydrolase characterized from T4SS in 89K pathogenicity island of epidemic Streptococcus suis serotype 2
1 Department of Microbiology, Third Military Medical University, Chongqing 400038, China
2 Department of Scientific Research, Daping Hospital, Research Institute of Surgery, Third Military Medical University, Chongqing 400042, China
3 PLA Research Institute of Clinical Laboratory Medicine, Nanjing general hospital of Nanjing Military command, Nanjing 210002, China
4 State Key Laboratory for Diagnosis and Treatment of Infectious Disease, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou 310003, China
BMC Microbiology 2014, 14:73 doi:10.1186/1471-2180-14-73Published: 22 March 2014
Streptococcus suis serotype 2 (S. suis 2) has evolved efficient mechanisms to cause streptococcal toxic shock syndrome (STSS), which is a new emerging infectious disease linked to S. suis. We have previously reported that a type IV secretion system (T4SS) harbored by the specific 89K pathogenicity island (PAI) of S. suis 2 contributes to the development of STSS and mediates horizontal transfer of 89K. However, the 89K T4SS machinery assembly in vivo and in vitro is poorly understood, and the component acting directly to digest the bacterial cell wall needs to be identified.
The virB1-89K gene product encoded in the 89K PAI is the only one that shows similarity to the Agrobacterium VirB1 component and contains a conserved CHAP domain that may function in peptidoglycan hydrolysis, which makes it a plausible candidate acting as a hydrolase against the peptidoglycan cell wall to allow the assembly of the T4SS apparatus. In the current study, the CHAP domain of VirB1-89K from S. suis 89K PAI was cloned and over-expressed in Escherichia coli, and its peptidoglycan-degrading activity in vitro was determined. The results indicated that the VirB1-89K CHAP domain can degrade the peptidoglycan layer of bacteria. Deletion of virB1-89K reduces significantly, but does not abolish, the virulence of S. suis in a mouse model.
The experimental results presented here suggested that VirB1-89K facilitates the assembly of 89K T4SS apparatus by catalyzing the degradation of the peptidoglycan cell wall, thus contributing to the pathogenesis of S. suis 2 infection.