New Heterothallic species of Hansenula II. Hansenula bimundalis and variety Americana

Summary

Hansenula bimundalis occurs in a line of heterothallic species that have coniferous trees for their habitats. This yeast is the last of its phylogenetic line to be isolated from nature exclusively as haploid vegetative cells. The next species above it, as the genus is at present constituted, isHansenula wingei Wickerham, which occurs in nature as both diploid and haploid vegetative cells. Some of them do possess the sexual agglutination process, others do not.H. bimundalis is not sexually agglutinative, but the species has stronger sexual reactions than its variety. In the laboratory, opposite sexes of the species mate more quickly and more abundantly, besides producing more ascospores and more diploid vegetative cells than the variety; the species also depends less upon tubes to effect conjugation. Although all strains of the variety conjugate with strains of the species, the hybrid zygotes do not produce ascospores. All nine strains of the species assimilate D-arabinose, but none of the five strains of the variety do. Evidently individuals of a common ancestral species became separated geographically some millions of years ago, the itinerant group developed into the species, and the indigenous ancestor developed into the variety. The perfect species and its variety have been placed inHansenula, and the separate mating types have been placed in the imperfect genusCandida. Latin descriptions of all four taxa have been included in this paper.