Staphylococcus aureus Trigger factor is involved in biofilm formation and cooperates with the chaperone PpiB

Peptidyl-prolyl cis/trans isomerases (PPIases) are enzymes that assist in protein folding around proline-peptide bonds, and often possess chaperone activity. Staphylococcus aureus encodes three PPIases; PrsA, PpiB and Trigger factor (TF). Previous work by our group demonstrated a role for both PrsA and PpiB in S. aureus, however, TF remains largely unstudied. Here, we identify a role for TF in S. aureus biofilm formation, and demonstrate cooperation between TF and the cytoplasmic PPIase PpiB. Mutation of the tig gene (encoding TF) leads to reduced biofilm development in vitro but no significant attenuation of virulence in a mouse model of infection. To determine if TF contributes to biofilm formation via chaperone activity, we analyzed the ability of a tig mutant to survive acid and basic stress. While there was no significant decrease in a tig mutant, a ppiB/tig double mutant exhibited a significant decrease in cell viability after acid and base challenge. We then demonstrate that a ppiB/tig double mutant has exacerbated phenotypes in vitro and in vivo when compared to either single mutant. Finally, in vivo immunoprecipitation of epitope tagged PpiB reveals that PpiB interacts with four times the number of proteins when TF is absent from the cell, suggesting it may be compensating for the loss of TF. Interestingly, the only proteins found to interact with TF are TF itself, FnBPB and the chaperone protein ClpB. Collectively, these results support the first phenotype for S. aureus TF and demonstrate a greater network of cooperation between chaperone proteins in Staphylococcus aureus.