Genetic and physiological variants of yeast selected from palm wine.

Genetic screening of 1200-palm wine yeasts lead to the selection of fourteen isolates with various genetic and physiological properties. Nine of the isolates were identified as Saccharamyces species, three as Candida species, one as Schizosaccharomyces species and one as Kluyveromyces species. Five of the isolates were wild type parents, two were respiratory deficient mutants (rho) and nine were auxotrophic mutants. Four isolates were heterozygous diploid (alphaa) and two were homozygous diploid (aa/alphaalpha) for the mating a mating types were further identified on mating with type loci. Four Mat alpha and four Mat a types were further identified on mating with standard haploid yeast strains. Forty-five percent sporulated on starvation medium producing tetrads. Fifty-two percent of the four-spored asci contained four viable spores. Maximum specific growth rate [micromax] of the fourteen isolates range from 0.13-0.26, five isolates were able to utilize exogenous nitrate for growth. Percentage alcohol production range between 5.8-8.8% for palm wine yeast, 8.5% for bakers' yeast and 10.4% for brewers yeast. The palm wine yeast were more tolerant to exogenous alcohol but had a low alcohol productivity. Hybridization enhanced alcohol productivity and tolerance in the palm wine yeasts.