Collectively, the results from these studies indicate that expression of Ahps in general is upregulated not only by oxidative factors but also by other stresses, such as drought Caspase activity and salinity. Hydrogen peroxide level is known to increase within the cell in response to various stress factors and act as an intracellular messenger for induction of genes related to defense against oxidative environments [37]. Treatment of cells with hydrogen peroxide mimics stress and induces defense signaling by activating mitogen-activated protein kinase and stimulates cell growth [38]. The ROS levels of D.

hansenii, S. cerevisiae and P. methanolica also increase in response to salt and methanol treatments, and the degrees of increase are more pronounced in the two salt-sensitive yeast species than the halophilic D. hansenii (Fig. 11). Furthermore, the DhAHP overexpression transformants of these species have reduced CT99021 order amounts of ROS accumulated than their wild type strains, indicating the protective role of Ahp. These results are in agreement with the earlier observations that Ahp genes play an important role in peroxide resistance in Bacillus subtilis [23], Clostridium pasteurianum [24], Burkholderia cenocepacia [25], Shewanella putrefaciens [35] and Porphyromonas gingivalis [39] under various stress conditions (e.g. hydrogen peroxide, high/low temperature

and high/low pH). Therefore, the induced expression and selleck products accumulation of DhAhp in saline environments to detoxify ROS is a very important survival mechanism for this halophilic organism. Conclusion In summary, the Ahp gene isolated from the extremely halophilic

yeast D. hansenii under salt stress in this study is a new gene relative to its salt tolerance mechanism. It is rapidly induced and accumulates to large quantities in D. hansenii to reduce accumulation of ROS. Molecular characterization shows that DhAhp, a cytosolic protein, belongs to the alkyl hydroperoxide reductase of the 1-Cys type peroxiredoxin family. The DhAhp and C. albicans Ahp11 have a common ancestry but show divergent evolution. Silencing of its expression by RNA interference resulted in decreased CYTH4 tolerance to salt stress. On the other hand, overexpression of the DhAHP in D. hansenii and the two salt-sensitive yeasts S. cerevisiae and P. methanolica conferred enhanced tolerance to salt with reduced accumulation of ROS. Clearly, the multiple activities (peroxidase, chaperone, redox signaling) possessed by Ahps are essential for its central role in protecting the cellular metabolism of yeast against ROS built-up under stress conditions. Compared with the two salt-sensitive yeasts, the extreme halotolerance exhibited by D. hansenii may be due to its ability to scavenge ROS by Ahp. Thus, the results of this study contribute to our understanding of the underlying mechanisms by which the extremely halophilic yeast D. hansenii adapts to high salt.