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

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, AtlASS , comprising the special GW module and N-acetylmuramidases domain, was designated as a putative autolysin. Indeed, the atlASS deletion mutant almost completely lost its activity in Triton X-100 induced bacterial autolysis, while the wild-type and CΔatlASS strains showed significant decrease, to less than 20% of the initial OD600 values. Unexpectedly, both immunofluorescence and immunogold electron microscopy confirmed that AtlASS 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 AtlASS mutation was reduced ˜ 40%, as compared to the wild-type strain. The ΔatlASS strain also attenuated bacterial adherence in human brain microvessel endothelial cells (HBMECs). Furthermore, we confirmed that AtlASS has fibrinogen/fibronectin binding capacities. In mouse infection model, the AtlASS inactivation also significantly attenuated bacterial virulence and proliferation in vivo. In conclusion, these results indicate that AtlASS autolysin modulates bacterial chain length, and contributes to the full virulence of SS during infection.