Five new combinations in the yeast genus Zygofabospora Kudriavzev emend. G. Naumov (pro parte Kluyveromyces) based on genetic data.

The rDNA sequencing data obtained during the last 5 years in several laboratories clearly demonstrate that within the heterogeneous genus Kluyveromyces there is a group of highly related species, which we refer to as the genus Zygofabospora Kudriavzev 1960 emend. G. Naumov 2002. This genus includes four hybridizing species, Zf. marxiana, Zf. dobzhanskii, Zf. lactis, Zf. wickerhamii (Zygofabospora sensu stricto), and two taxonomically related species, Zf. aestuarii, Zf. nonfermentans (Nagahama et al.) G. Naumov comb. nov. (Zygofabospora sensu lato). We studied the relationships of the yeasts composing the Zf. lactis complex. Genetic hybridization analysis and molecular karyotyping revealed partial genetic-isolation varieties, Zf. lactis var. drosophilarum (Shehata et al.) G. Naumov comb. nov. and Zf. lactis var. phaseolospora (Shehata et al.) G. Naumov comb. nov. from North America, and Zf. lactis var. krassilnikovii (Kudriavzev) G. Naumov comb. nov. from Europe. The dairy yeast Zf. lactis var. lactis G. Naumov comb. nov. yields highly fertile hybrids with its wild ancestor Zf. lactis var. krassilnikovii and semi-sterile hybrids with North American taxa. Besides, Zf. lactis var. lactis and Zf. lactis var. krassilnikovii formed fertile hybrids with the South African yeast Zf. lactis var. vanudenii (van der Walt et Nel) G. Naumov comb. nov. The reinstatement of the latter yeast at the variety level has been done taking into account the results of the present study and the literature data on its geographic isolation, high divergence of the karyotype and mitochondrial DNA.