The Fem system in Pseudomonas aeruginosa functions as an ExsA-regulated interspecies signaling pathway

Bacterial interspecies interactions shape the function and structural dynamics of microbial communities and affect disease progression of polymicrobial infections. Here, we present data suggesting that the FemA-FemR-FemI (Fem) cell surface signaling system in P. aeruginosa serves as an interspecies signaling pathway between P. aeruginosa and Mycobacterium species. The Fem system is regulated by the type three secretion system (T3SS) regulator ExsA. Fem system significantly influenced virulence factors in P. aeruginosa, including the quorum sensing systems, pyocyanin production, biofilm formation and the type six secretion systems (T6SSs). Our study using a Galleria mellonella infection model indicates femA deletion significantly increased the host survival rate while femI over-expression decreased it, demonstrating that the Fem system’s role in bacterial pathogenicity in vivo. We propose that the Fem system functions as an interspecies signaling pathway enabling P. aeruginosa to alter its behaviours in response to the presence of mycobacteria. Gene expression was compared between wild-type P. aeruginosa PAO1 and femI deletion mutant in the presence and absence of Mycobactin J.