The role of HIL1 in Strain-Level Adhesion and Immune Recognition in Debaryomyces hansenii

Abstract Strains of food-derived microbes can become facultative pathogens in susceptible human hosts. Surprisingly, we previously isolated Debaryomyces hansenii, a yeast common in fermented foods, from Crohn disease (CD) ulcers, raising questions about its strain-specific traits that influence host interactions. Here, we further developed the genetic tractability of D. hansenii and identified a single adhesin, Hil1, as a major determinant of colony morphology, biofilm formation, and immune targeting in CD patients. We used Agrobacterium tumefaciens-mediated transformation to perform a forward genetic screen in a food‑derived reference strain. We isolated mutants that converted from a wrinkled, biofilm‑forming phenotype to a smooth, non‑adherent phenotype characteristic of CD patient isolates. Mapping of multiple insertion sites showed a disrupted subtelomeric Hyr/Iff‑like adhesin gene, herein as HIL1. CRISPR‑Cas9 mediated deletion of HIL1 recapitulated the mutant phenotype, demonstrating that HIL1 was necessary for biofilm formation and high cell‑surface hydrophobicity phenotypes. To contextualize these findings, we performed comparative genomics on a D. hansenii strain collection to assess allelic variation in the number of HIL1 tandem repeats. Longer alleles in food strains correlated with increased biofilm formation while CD-isolated strains contained shorter HIL1 alleles and reduced binding to surfaces. Serology profiling showed that HIL1 was a direct antigenic target of circulating immunoglobulin G (IgG) in CD patients. Together, these results suggest Hil1 is a key, strain‑variable adhesin shaping fungal surface properties and host immune recognition. This work establishes D. hansenii as a genetically tractable system and shows how adhesin polymorphisms may influence fungal behavior in food and disease contexts.