Characterization of a salt-induced DhAHP, a gene coding for alkyl hydroperoxide reductase, from the extremely halophilic yeast Debaryomyces hansenii

By using forward subtractive hybridization we have cloned and sequenced DhAHP from D. hansenii that is significantly upregulated during salinity stress. DhAHP is orthologous to the alkly hydroperoxide reductase of the peroxiredoxin gene family, which catalyzes the reduction of peroxides at the expense of thiol compounds. The full-lengthed cDNA of DhAHP has 674 bp of nucleotide and contains a 516 bp open reading frame (ORF) encoding a deduced protein of 172 amino acid residues (18.3 kDa). D. hansenii Ahp is a cytosolic protein that belongs to the Ahp of the 1-Cys type peroxiredoxins. Phylogentically, the DhAhp and Candida albicans Ahp11 (Swiss-Prot: Q5AF44) share a common ancestry but show divergent evolution. Silence of its expression in D. hansenii by RNAi resulted in decreased tolerance to salt whereas overexpression of DhAHP in D. hansenii and the salt-sensitive yeasts Saccharomyces cereviasiae and Pichia methanolica conferred a higher tolerance with a reduced level of reactive oxygen species.In conclusion, for the first time our study has identified alkly hydroperoxide reductase as a key protein involved in the salt tolerance of the extremely halophilic D. hansenii. Apparently, this enzyme plays a multi-functional role in the yeast's adaptation to salinity; it serves as a peroxidase in scavenging reactive oxygen species, as a molecular chaperone in protecting essential proteins from denaturation, and as a redox sensor in regulating H2O2-mediated cell defense signaling.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 tolerate salinity levels up to 24% (4.11 M) of NaCl [2]. In contrast, growth of the Baker's yeast Saccharomyces cerevisiae is severely inhibited when salinity reaches 10% NaCl [3]. Thus, D. hanseni