The Saccharomyces cerevisiae ∑1278b strain is sensitive to NaCl because of mutations in its ENA1 gene

Most laboratory strains of the yeast Saccharomyces cerevisiae are incapable of invading agar, to form large colonies (mats), and to develop filament-like structures (pseudohyphae). A prominent strain that manifests these morphologies is ∑1278b. While induced transcription of the FLO11 gene is critical for executing invasive growth, mat formation, and pseudohyphal growth, downregulation of the 'general stress response' also seems to be required. As this response is weak in ∑1278b cells, we assumed that they may be sensitives to stresses. We report, however, that they are resistant to various stressors, but severely sensitive specifically to NaCl. We found that this sensitivity is a result of mutations in the single ∑1278b's ENA gene, encoding P-type sodium ATPase. Other laboratory strains harbor three to five copies of ENA, suggesting that ∑1278b was selected against Ena activity. Obtaining ∑1278b cells that can grow on NaCl allows checking its effect on colony morphologies. In the presence of NaCl, ∑1278b/ENA1+ cells do not invade agar, and do not form pseudohyphae or mats. Thus, we have found the following: (i) The ∑1278b strain differs from other laboratory strains with respect to sensitivity to NaCl, because it has no active Na+ ATPase exporter. (ii) NaCl is a suppressor of invasiveness, filamentous growth, and mat formation.