Isolation and characterisation of mutants from the halotolerant yeast Pichia sorbitophila defective in H+/glycerol symport activity.

Pichia sorbitophila, a yeast species that is highly resistant to osmotic stress in general and to salt stress in particular, was subjected to a mutagenesis strategy in order to obtain mutants deficient in the glycerol active uptake previously described. Density centrifugation was used for enrichment of NaCl sensitive mutants in either glucose or glycerol media. Several phenotypic classes of mutants were identified, to which physiological tests were applied concerning the activity of the symporter, its accumulation capacity and the detection of the activity of glycerol pathway specific enzymes. From these, two mutant strains were selected, presenting a clearly deficient phenotype on H+/glycerol symport activity.