Altered Innate Immunity Confers Staphylococcus aureus Resistance in O-glycosylation Deficient Caenorhabditis elegans bus Mutants

The Caenorhabditis elegans bus (bacterial unswollen) mutants were isolated by their altered response to the nematode pathogen Microbacterium nematophilum. The bus-2, bus-4 and bus-17 mutants are resistant to infection by this bacterium and to infection by human pathogens Yersinia pestis and Yersinia pseudotuberculosis. Here we extend that list to Staphylococcus aureus. The bus-2, bus-4 and bus-17 mutants each harbors a defect in a different glycosyltransferase involved in O-glycosylation. Glycomics analysis of these strains reveals significant O-glycosylation defects. We further investigated the nature of bus mutant phenotypes in bus-2, bus-4 and bus-17 by gene expression analysis. Three distinct areas of altered expression were identified: 1) N- and O-glycosylation; 2) innate immune response; 3) protein folding and editing control. As expected N- and O-glycosylation gene expression was altered at key enzymatic steps. Innate immune system expression patterns were altered in a way that significantly overlapped with expression patterns seen in wild-type upon exposure to Staphylococuss aureus. Upon infection with S. aureus markers of innate immune activity increased significantly compared to wild-type. The abu/pqn genes, active in the non-canonical unfolded protein response (UPR) pathway were dramatically upregulated in bus when these mutants were exposed to the pathogen. This work demonstrates a genetic link between O-glycosylation and expression of key components of the innate immune response. Identification of genes expressed in three groups with 5 groups three replications (N2D as control)