RB-R performed Western blot analysis, GH, RT and RS provided the diagnostic assays. GH performed all other experiments. RS supervised the experimental work and the interpretation

of data and planned the manuscript. EL provided funding. GH and RS wrote the paper. All authors analysed the data, commented on and approved the manuscript.”
“Background Debaryomyces hansenii is an ascomycetous salt- and high pH-tolerant yeast that has been defined as halotolerant or halophilic [1]. It was isolated from saline environments such as sea water [2] or concentrated brines [3], representing one of the most salt tolerant species of yeasts. This marine yeast can Semaxanib tolerate salinity levels up to 24% (4.11 M) of NaCl [2]. In contrast, growth of the Baker’s yeast Saccharomyces cerevisiae is severely Mizoribine clinical trial inhibited when salinity reaches 10% NaCl [3]. Thus, D. hansenii has become a model organism for the study of salt tolerance mechanisms in eukaryotic cells [4]. It is now well recognized that the mechanisms by which all organisms achieve osmotic and ionic equilibrium are mediated by orthologous

NVP-BEZ235 mechanisms based on conserved biochemical and/or physiological functions that are inherently necessary for essential metabolic processes [5]. Under saline conditions, D. hansenii accumulates large amounts of Na+ without being intoxicated even when K+ is present at low concentration in the environment [6]. In fact, Na+ improves growth and protects D. hansenii in the presence

of additional stress factors [1]. For example, at high or low temperature and extreme pH growth of the yeast Bay 11-7085 is improved by the presence of 1 M NaCl [7]. It has been clearly shown that sodium ions are less toxic for D. hansenii as compared with other organisms; therefore, it is considered a ‘sodium-includer’ organism [8]. The reduced toxic effect by Na+ and its accumulation at high levels under high salt is probably indicative of an adaptive strategy of D. hansenii for growth in hypersaline environments [9]. The organism must posses an array of advantageous characteristics that collectively confer its high halotolerance. Earlier studies have identified a number of salt-related genes in the extreme halophilic yeast D. hansenii, such as HOG1 (MAP kinase involved in high-osmolarity glycerol synthesis pathway) [10], ENA1 and ENA2 (plasmamembrane Na+-ATPase [11], GPD1 and GPP (NAD-glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase) [12], NHX1 (vacuolar Na+ antiporter) [13] and KHA1 (Na+/H+ antiporter) [14]. As expected, most of these salt-upregulated genes are involved in osmoregulation or transport of ions. However, the collective underlying mechanisms by which D. hansenii tolerates high levels of NaCl remain unkown. All aerobic organisms require oxygen for efficient production of energy, but at the same time the organisms are constantly exposed to oxidative stress. This can be caused by partially reduced forms of molecular oxygen (e.g.