Characterization of the Phase-Variable Autotransporter Lay Reveals a Role in Host Cell Adherence and Biofilm Formation in Nontypeable Haemophilus influenzae

Lay is an autotransporter protein found in pathogenic Haemophilus and Neisseria species. Lay in nontypeable Haemophilus influenzae (NTHi) is phase-variable: the gene reversibly switches ON-OFF via changes in length of a locus-located GCAA((n)) simple DNA sequence repeat tract. The expression status of lay was examined in carriage and invasive collections of NTHi, where it was predominantly not expressed (OFF). Phenotypic study showed lay expression (ON) results in increased adherence to human lung cells and denser biofilm formation. A survey of Haemophilus species genome sequences showed lay is present in similar to 60% of NTHi strains, but lay is not present in most typeable H. influenzae strains. Sequence analysis revealed a total of five distinct variants of the Lay passenger domain present in Haemophilus spp., with these five variants showing a distinct lineage distribution. Determining the role of Lay in NTHi will help understand the role of this protein during distinct pathologies.