Plasma membrane H+ and K+ transporters are involved in the weak-acid preservative response of disparate food spoilage yeasts

The food spoilage yeasts Zygosaccharomyces bailii and Saccharomyces cerevisiae have been proposed to resist weak-acid preservative stress by different means; Z bailii by limiting influx of preservative combined with its catabolism, S. cerevisiae by active extrusion of the preservative weak-acid anion and H+. Measurement of H+ extrusion by exponential-phase Z. bailii cells suggest that, in common with S. cerevisiae, this yeast uses a plasma membrane H+-ATPase to expel H+ when challenged by weak-acid preservative (benzoic acid). Simultaneous measurement of Z. bailii net H+ and K+ fluxes showed that net K+ influx accompanies net H+ efflux during acute benzoic acid stress. Such ionic coupling is known for S. cerevisiae in short-term preservative stress. Both yeasts significantly accumulated K+ on long-term exposure to benzoic acid. Analysis of S. cerevisiae K+ transporter mutants revealed that loss of the high affinity K+ uptake system Trk1 confers sensitivity to growth in preservative. The results suggest that cation accumulation is an important factor in adaptation to weak-acid preservatives by spoilage yeasts and that Z. bailii and S. cerevisiae share hitherto unsuspected adaptive responses at the level of plasma membrane ion transport. © 2005 SGM.