The type VI secretion system of the emerging pathogen Stenotrophomonas maltophilia complex has antibacterial properties

Abstract

ABSTRACT Antagonistic behaviors between bacterial cells can have profound effects on microbial populations and disease outcomes. Polymicrobial interactions may be mediated by contact-dependent proteins with antibacterial properties. The type VI secretion system (T6SS) is a macromolecular weapon used by Gram-negative bacteria to translocate proteins into adjacent cells. Many pathogens deploy the T6SS to escape immune cells, eliminate commensal bacteria, and facilitate infection. Stenotrophomonas maltophilia complex is a Gram-negative opportunistic pathogen that primarily affects immunocompromised people and infects the lungs of patients with cystic fibrosis. Infections with the bacterium can be deadly and are challenging to treat because many isolates are multidrug-resistant. We found that globally dispersed S. maltophilia complex clinical and environmental strains possess T6SS genes. We demonstrate that the T6SS of an S. maltophilia complex patient isolate is active and can eliminate other bacteria. We provide evidence that the T6SS contributes to the competitive fitness of S. maltophilia complex against a co-infecting Pseudomonas aeruginosa isolate, and the T6SS alters the organization of S. maltophilia and P. aeruginosa co-cultures. This study expands our knowledge of the mechanisms employed by S. maltophilia complex to secrete antibacterial proteins and compete against other bacteria. IMPORTANCE Infections with the opportunistic pathogen Stenotrophomonas maltophilia complex can be fatal for immunocompromised patients. The mechanisms used by the bacterium to compete against other prokaryotes are not well understood. We found that the type VI secretion system (T6SS) allows S. maltophilia complex to eliminate other bacteria and contributes to the competitive fitness against a co-infecting isolate. The presence of T6SS genes in isolates across the globe highlights the importance of this apparatus as a weapon in the antibacterial arsenal of S. maltophilia complex. The T6SS may confer survival advantages to S. maltophilia complex isolates in polymicrobial communities in both environmental settings and during infections.