Differences in activation of MAP kinases and variability in the polyglutamine tract of Slt2 in clinical and non-clinical isolates of Saccharomyces cerevisiae.

The concept of Saccharomyces cerevisiae as an emerging opportunistic pathogen is relatively new and it is due to an increasing number of human infections during the past 20 years. There are still few studies addressing the mechanisms of infection of this yeast species. Moreover, little is known about how S. cerevisiae cells sense and respond to the harsh conditions imposed by the host, and whether this response is different between clinical isolates and non-pathogenic strains. In this regard, mitogen-activated protein kinase (MAPK) pathways constitute one of the major mechanisms for controlling transcriptional responses and, in some cases, virulence in fungi. Here we show differences among clinical and non-clinical isolates of S. cerevisiae in the level of activation of the MAPKs Kss1, which controls pseudohyphal and invasive growth, and Slt2, which is required for maintaining the integrity of the cell wall under stress conditions and in the absence of stimulating conditions. Moreover, we report for the first time the existence of length variability in SLT2 alleles of strains with a clinical origin. This is due to the expansion in the number of glutamine-encoding triplets in the microsatellite region coding for the polyglutamine (poly-Q) tract of this gene, which range from 12 to more than 38 repetitions. We suggest that this variability may influence biological features of the Slt2 protein, allowing it to adapt swiftly in order to survive in unusual environments.