Schizosaccharomyces lindneri sp. nov., a fission yeast occurring in honey.

Two strains of fission yeast were isolated from honey. They differ from the type strain of Schizosaccharomyces octosporus by three substitutions in the D1/D2 domain of the nuclear 26S large subunit ribosomal RNA (rRNA) gene sequence, resulting in a 99.5% identity. In the internal transcribed spacer (ITS) region (consisting of ITS1, 5.8S rDNA, and ITS2), the strains differ from S. octosporus by 16 gaps and 91 substitutions, which is equivalent to an identity of 88.1%. Genome sequencing on one of the new strains revealed that the average nucleotide identity (ANI) between its genome and the reference genome of S. octosporus is 90.43% and there exist major genome rearrangements between the two genomes. Mating analysis revealed that S. octosporus and one of the new strains are completely reproductively separated. A strong prezygotic barrier exists and the few mating products consist of diploid hybrids that do not form recombinant ascospores. In the new strains, asci are either zygotic, arising from conjugation, or they develop without conjugation from asexual cells (azygotic). Compared to the currently recognized Schizosaccharomyces species, the spectrum of nutrients that are assimilated by the new strains is restricted. Of the 43 carbohydrates that were included in the physiological standard tests, only 7 were assimilated. According to the results of the genome sequence analysis, the mating trials, and the phenotypic characterization, the new species Schizosaccharomyces lindneri is described to accommodate the two strains (holotype: CBS 18203T  and ex-type: MUCL 58363; MycoBank no.: MB 847838).

Insights into the ecology of Schizosaccharomyces species in natural and artificial habitats.

The fission yeast genus Schizosaccharomyces contains important model organisms for biological research. In particular, S. pombe is a widely used model eukaryote. So far little is known about the natural and artificial habitats of species in this genus. Finding out where S. pombe and other fission yeast species occur and how they live in their habitats can promote better understanding of their biology. Here we investigate in which substrates S. pombe, S. octosporus, S. osmophilus and S. japonicus are present. To this end about 2100 samples consisting of soil, tree sap fluxes, fresh fruit, dried fruit, honey, cacao beans, molasses and other substrates were analyzed. Effective isolation methods that allow efficient isolation of the above mentioned species were developed. Based on the frequency of isolating different fission yeast species in various substrates and on extensive literature survey, conclusions are drawn on their ecology. The results suggest that the primary habitat of S. pombe and S. octosporus is honeybee honey. Both species were also frequently detected on certain dried fruit like raisins, mango or pineapple to which they could be brought by the honey bees during ripening or during drying. While S. pombe was regularly isolated from grape mash and from fermented raw cacao beans S. octosporus was never isolated from fresh fruit. The main habitat of S. osmophilus seems to be solitary bee beebread. It was rarely isolated from raisins. S. japonicus was mainly found in forest substrates although it occurs on fruit and in fruit fermentations, too.