The Debaryomyces hansenii NHA1 gene encodes a plasma membrane alkali-metal-cation antiporter with broad substrate specificity

Abstract

Debaryomyces hansenii is a yeast species often found in salty environments. Its genome sequence is known completely, but the mechanisms behind its halotolerance are poorly understood. In the D. hansenii genome, there is a gene strongly homologous to the Saccharomyces cerevisiae NHA1 gene (encoding a plasma membrane Na +/H + antiporter). We isolated this DhNHA1 gene from two D. hansenii strains (CBS 767 and CBS 1793) differing in their osmotolerance. Both DhNHA1 alleles were heterologously expressed in a S. cerevisiae strain lacking its own systems for the efflux of alkali metal cations (BW31a, ena1–4Δ nha1Δ). D. hansenii Na +/H + antiporters were localized in the plasma membrane of BW31a cells, their presence increased BW31a tolerance to sodium, potassium, lithium and also rubidium. Measurements of Na + and K + efflux from S. cerevisiae cells expressing DhNHA1 alleles show that the D. hansenii antiporters efficiently transported both cations out of cells. The sodium and potassium transport activity of Nha1 antiporters from both D. hansenii strains was almost identical, indicating that plasma membrane antiporter activity is not one of the factors determining the different levels of halotolerance in the two strains.