Kluyveromyces osmophilus, a new yeast species
In 1962 Dr. R. ANTOINE of Mauritius sent a number of yeast strains isolated from sugar for identification to the Yeast Division of the Centraalbureau voor Schimmelcultures at Delft. One of these strains is considered to belong to a new species for which the name Kluyverornyces osmophilus is proposed. It will be described in the following part. This yeast strain was conspicuous by forming oval to reniform spores which were easily liberated from the ascus. When first studied, sporulation was abundant. The picture of the spores in this paper. (fig 2) is an electron micrograph of ultra-thin sections of a preparation fixed at that time with osmic acid and uranyl acetate according to RYTER et al. (1958). Unfortunately, the sporulating ability has been lost after maintaining the yeast for two years on malt agar. The yeast, grown on malt agar, was investigated according to the methods of WICKERHAM (1951) and of LODDER & KREGERVAN RIJ (1952). As regards the fermentation and assimilation reactions some remarks can be made. Fermentation of a 2% (w/v) glucose solution in a Durham tube was rather slow, i.e. the insert tube was filled up with gas after 10--14 days' incubation at 25 ° C. A 10% glucose solution gave the same result after 5--7 days, while a 30% glucose solution had a gas-filled insert tube after 5 days. Apparently, in solutions with a higher sugar concentration the fermentation rate was high at an earlier period. The assimilation test with the auxanographic method gave positive results for glucose and galactose only. The assimilation test in a synthetic liquid medium with glucose as the sole source of carbon in a concentration of 0 .50, read after one week at 25 ° C, show-
Molecular evidence for the existence of natural hybrids in the genus Zygosaccharomyces.
26S rDNA D1/D2 sequencing was used to characterise a number of food-associated Zygosaccharomyces rouxii strains held at the National Collection of Yeast Cultures. In the course of this study, four strains (NCYC 1682, NCYC 3042, NCYC 3060 and NCYC 3061) were identified which appeared, based on their D1/D2 sequences, to belong to a novel Zygosaccharomyces species. However, subsequent sequence analysis showed that NCYC 1682, NCYC 3060 and NCYC 3061 possess two highly divergent copies of the nuclear-encoded ADE2, HIS3 and SOD2 genes, indicating these three strains are in fact hybrids. NCYC 3042, however, does appear to represent a novel species which may be hypothesized to have crossed with Z. rouxii and given rise to hybrid strains. Additional approaches to define precise taxonomic status and mechanisms of hybrid genome formation amongst yeast species are discussed.
Saccharomyces vanudenii Nov. Spec.
During studies on the yeast flora associated with winery installations three strains of a hitherto undescribed homothallic yeast species were recovered from wineries in the S.W. Cape Province at Stellenbosch, Koelenhof and Vlottenburg. The following description of the species is based on the standard taxonomical procedures outlined by LODDER ~Z KREGER-VAN ]RIJ (1952) and WICKERHAM (1951) and WICKERHAM & BURTON (1956a, b).