Megan McClean

Pathogenic microbial populations display large amounts of heterogeneity in stress and drug resistance. Often this heterogeneity is due to non-genetic differences, that is, differences between cells that are not due to mutations in the DNA. One source of phenotypic heterogeneity in cells is heterogeneity in gene expression. We published the first study of single-cell gene expression in yeast before and after a model stress (hyperosmotic stress). Using single-cell microscopy and reporters of transcription factor activity, we determined that fluctuations in transcription factor (TF) activity are driving part of the gene expression heterogeneity visible in the data but also that there is substantial buffering of noisy TF activity. We have generated light-controlled transcription factors and are using them to generate pulses of transcription factor activity to elucidate how promoters decode transcription factor pulses and how noisy decoding contributes to cell-to-cell variability in gene expression and phenotypic heterogeneity.

Heterogeneity is also important in understanding biofilm development and the progression of disease caused by pathogenic yeasts. We have developed microfluidic technology that allows us to grow pathogenic yeast biofilms and measure virulence phenotypes such as dispersed cell number and phenotype. We are developing optogenetic tools in pathogenic yeasts so that we can identify the role of specific genetic regulators in driving disease. In parallel, we have developed optogenetic approaches to control microbial community structure, for example, by controlling the location and number of producer or cheater cells.