C. mastitidis requires the protein Sortase F to colonize the eye.

The ocular surface is a mucosal tissue that is constantly exposed to environmental antigens and potential pathogens. Human microbiomes play a critical role in the balance of surveillance and inflammation at sites of colonization. Historically, the investigation of the ocular microbiome has been difficult due to its paucibacterial nature and the inhospitable environment of the ocular surface. Despite this, Corynebacterium mastitidis ( C. mast ) developed a unique ability to colonize the eye and elicit a protective immune response characterized by induction of IL-17 from γδ T cells and protection from corneal infection. Therefore, we sought to understand the unique bacterial machinery that C. mast utilizes to colonize the eye and how it affects the induction of an eye-specific immune signature. Using a C. mast transposon mutant library, we identified a mutant that completely lacked an ability to form biofilm, colonize the eye, and induce in vivo immunity. Whole genome sequencing revealed a disruption in the sortase F gene, which anchors proteins to the cell wall of C. mast , governing biofilm formation and tethering of adhesins to the cell surface. Additionally, we show that mutation in individual C. mast adhesins does not affect ocular colonization or immune induction. By understanding the molecular mechanism of ocular microbial colonization, this work advances our understanding of how bacteria colonize and induce immune responses on the eye, providing a foundation for developing novel therapeutic strategies against ocular infections.