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

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 CΔatlA_SS strains showed significant decrease, to less than 20% of the initial OD₆₀₀ 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 ΔatlA_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.