ClpP participates in stress tolerance and negatively regulates biofilm formation in Haemophilus parasuis.

Haemophilus parasuis is generally considered a commensal organism in the upper respiratory tract of pigs, where it evades the host immune system and survives the challenging host environment. In response to various host stresses, H. parasuis strains can adapt to the adverse conditions. However, the specific bacterial factors that participate in this process are poorly understood. Here, we investigated the role of ClpP in H. parasuis virulent strain CF7066 by generating a clpP deletion mutant (ΔclpP), as well as a complemented strain C-clpP. Our findings supported that ClpP is essential for stress tolerance of H. parasuis, by the demonstrations that the ΔclpP mutant showed decreased resistance to heat, oxidation, and osmotic pressure. Notably, we observed increased autoagglutination and biofilm formation in the ΔclpP mutant and the amount of polysaccharides and extracellular proteins, which are the main components of biofilm, were much higher in the ΔclpP mutant than the wild-type strain. Real-time PCR demonstrated that the transcriptional regulators csrA and rpoD, and a possible biofilm repressor luxS were significantly downregulated upon clpP deletion. Together, these observations suggest that ClpP plays an essential role in stress tolerance, and negatively regulates biofilm formation in H. parasuis.