Abstract
Debaryomyces hansenii is a halotolerant yeast that produces and assimilates a wide variety of polyols. In this work we evaluate polyol transport in D. hansenii CBS 767, detecting the occurrence of polyol/H+ (and sugar/H+) symporter activity, through the transient extracellular alkalinization of unbuffered starved cell suspensions. From the D. hansenii genome database, we selected nine ORFs encoding putative transporter proteins to clone in a centromeric plasmid with C-terminal GFP tagging and screened for polyol/H+ symporters by heterologous expression in Saccharomyces cerevisiae. Five distinct D. hansenii polyol/H+ symporters were identified and characterized, with different specificities and affinities for polyols, namely one glycerol-specific (DhStl1), one D-galactitol-specific (DhSgl1, Symporter galactitol/H+ 1), one D-(+)-chiro-inositol-specific (DhSyi1, Symporter D-(+)-chiro-inositol/H+ 1), one for D-sorbitol/D-mannitol/ribitol/D-arabitol/D-galactitol (DhSyl1, Symporter Polyols 1) and another for D-sorbitol/D-mannitol/ribitol/D-arabitol (DhSyl2, Symporter Polyols 2). This work contributed to the annotation of new yeast polyol transporters, including two specific for uncommon substrates as galactitol and D-(+)-chiro-inositol.
Highlights
In response to salt- and drought-stress, fungi, marine algae and vascular plants can synthesize and accumulate soluble compounds with low molecular weight
Taking into account that the yeasts from the genus Debaryomyces are among the ascomycete yeasts that assimilate a broader array of polyols [16] and that D. hansenii CBS 767 complete genome sequence is available, we studied polyol transport in more detail in this yeast
Detection of polyol/sugar symport activity in D. hansenii CBS 767 was only possible after starving the cells
Summary
In response to salt- and drought-stress, fungi, marine algae and vascular plants can synthesize and accumulate soluble compounds with low molecular weight. These compounds are designated as compatible solutes because they are compatible with cell metabolism, even when they accumulate at high intracellular concentrations. It has been suggested that polyols may mimic the structure of water and maintain an artificial sphere of hydration around macromolecules. They may act as scavengers of reactive oxygen species, thereby preventing peroxidation of lipids that would cause cell damage [1]
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