A novel autolysin AtlASS mediates bacterial cell separation during cell division and contributes to full virulence in Streptococcus suis.

• This is the first research to evaluate the biological functions of AtlA SS autolysin in SS. • AtlA SS was instrumental in cell separation and stress-induced autolysis. • AtlA SS contributes to biofilm formation, and also interacts specifically with fibrinogen and fibronectin. • Our results provide interesting insights into the role of AtlA SS in the pathogenesis of SS. Streptococcus suis (SS) is a major pathogen in the swine industry, and also an important zoonotic agent for humans. The novel SS cell surface protein, AtlA SS , comprising the special GW module and N -acetylmuramidases domain, was designated as a putative autolysin. Indeed, the atlA SS deletion mutant almost completely lost its activity in Triton X-100 induced bacterial autolysis, while the wild-type and CΔ atlA SS strains showed significant decrease, to less than 20% of the initial OD 600 values. Unexpectedly, both immunofluorescence and immunogold electron microscopy confirmed that AtlA SS is mainly located in the cell division septum, suggesting autolytic activity in peptidoglycan hydrolysis may be required for cell separation, thus modulating and truncating bacterial chain length. The biofilm capacity of the AtlA SS mutation was reduced ˜ 40%, as compared to the wild-type strain. The Δ atlA SS strain also attenuated bacterial adherence in human brain microvessel endothelial cells (HBMECs). Furthermore, we confirmed that AtlA SS has fibrinogen/fibronectin binding capacities. In mouse infection model, the AtlA SS inactivation also significantly attenuated bacterial virulence and proliferation in vivo. In conclusion, these results indicate that AtlA SS autolysin modulates bacterial chain length, and contributes to the full virulence of SS during infection. [ABSTRACT FROM AUTHOR]