Heterothallic strains belonging to the biologically distinct yeast species Clavispora opuntiae and Clavispora lusitaniae were studied by three different methods. The type cultures of the two yeast species exhibited 8% relatedness as measured by reassociation of unique deoxyribonucleic acid. Ten strains of C. opuntiae and nine strains of C. lusitaniae were compared on the basis of their physiological phenotypes and the restriction maps of their ribosomal deoxyribonucleic acid (rDNAs). Although the two species possessed many similarities as well as certain amounts of intraspecific variation by both approaches, they appeared to constitute well-defined entities. Unlike C. opuntiae, C. lusitaniae always utilized L-rhamnose as the sole carbon source and was resistant to 10 mg of cycloheximide per liter. Strains of C. opuntiae did not utilize L-lysine as the sole nitrogen source or utilized it very weakly, whereas all strains of C. lusitaniae grew rapidly on this compound. By contrast, the hydrolysis of Tween 80 and the utilization of lactic acid, citric acid, and hexadecane tended to be more pronounced in C. opuntiae. The rDNA repeating unit was 9.0 kilobases long in C. lusitaniae, as compared with 7.6 kilobases in C. opuntiae. The conserved region identified previously in the rDNA of C. opuntiae was found almost intact in the rDNA of C. lusitaniae, but the variable regions differed substantially between the two species.
Of 29 strains of various Saccharomyces spp., 24 gave generally similar chromosomal band patterns (14 to 17 bands in the size range from 200 to 2,000 kilobase pairs), as determined by orthogonal field alternation gel electrophoresis. However, most of these stains showed unique band patterns due to chromosome polymorphisms. Strains of Saccharomyces kluyveri, Candida albicans, Candida utilis, Kluyveromyces lactis, Pichia canadensis, and Schwanniomyces occidentalis gave bands that were indicative of small numbers of larger chromosomes (> 1,000 kilobase pairs). These results suggest that Saccharomyces kluyveri should be included in another genus and that Saccharomyces spp. may be different from other yeasts in having a large number of chromosomes, the majority of which are smaller than 1,000 kilobase pairs.