Heterogeneous Expression of the Virulence-Related Adhesin Epa1 between Individual Cells and Strains of the Pathogen Candida glabrata

We investigated the relevance of gene expression heterogeneity to virulence properties of a major fungal pathogen,Candida glabrata . The organism's key virulence-associated factors include glycosylphosphatidylinositol-anchored adhesins, encoded subtelomerically by theEPA gene family. Individual-cell analyses of expression revealed very striking heterogeneity for Epa1, an adhesin that mediates ∼95% of adherence to epithelial cellsin vitro . The heterogeneity in Epa1 was markedly greater than that known for other yeast genes. Sorted cells expressing high or low levels of Epa1 exhibited high and low adherence to epithelial cells, indicating a link between gene expression noise and potential virulence. The phenotypes of sorted subpopulations reverted to mixed phenotypes within a few generations. Variation in single-cell Epa1 protein and mRNA levels was correlated, consistent with transcriptional regulation of heterogeneity. Sir-dependent transcriptional silencing was the primary mechanism driving heterogeneous Epa1 expression inC. glabrata BG2, but not in CBS138 (ATCC 2001). Inefficient silencing in the latter strain was not due to a difference inEPA1 sequence or (sub)telomere length and was overcome by ectopicSIR3 expression. Moreover, differences between strains in the silencing dependence ofEPA1 expression were evident across a range of clinical isolates, with heterogeneity being the greatest in strains whereEPA1 was subject to silencing. The study shows how heterogeneity can impact the virulence-related properties ofC. glabrata cell populations, with potential implications for microbial pathogenesis more broadly.