Reinstatement of the fission yeast species Schizosaccharomyces versatilis Wickerham et Duprat, a sibling species of Schizosaccharomyces japonicus

Abstract

Schizosaccharomyces japonicus Yukawa et Maki (1931) and Schizosaccharomyces versatilis Wickerham et Duprat (1945) have been treated as varieties of S. japonicus or as conspecific, based on various approaches including mating trials and nDNA/nDNA optical reassociation studies. However, the type strains of S. japonicus and S. versatilis differ by five substitutions (99.15% identity) and one 1‐bp indel in the sequences of the D1/D2 domain of the 26S rRNA gene, and 23 substitutions (96.3% identity) and 31‐bp indels in the sequences of internal transcribed spacer (ITS) of rRNA, suggesting that they may not be conspecific. To reassess their taxonomic status, we conducted mating trials and whole‐genome analyses. Mating trials using the type strains showed a strong but incomplete prezygotic sterility barrier, yielding interspecies mating products at two orders of magnitude lower efficiency than intraspecies matings. These mating products, which were exclusively allodiploid hybrids, were unable to undergo the haplontic life cycle of the parents. We generated chromosome‐level gap‐less genome assemblies for both type strains. Whole genome sequences yielded an average nucleotide identity (ANI) of 86.4%, indicating clear separation of S. japonicus and S. versatilis. Based on these findings, we propose the reinstatement of S. versatilis as a distinct species (holotype strain: CBS 103T and ex‐types: NRRL Y‐1026, NBRC 1607, ATCC 9987, PYCC 7100; Mycobank no.: 847838).

New species, genome assemblies, and tools shed fresh light on fission yeasts

“…Previous attempts to establish whether these strains are conspecific yielded contrasting results and their taxonomic classification remained in dispute (Vaughan-Martini & Martini, 2011). This issue of Yeast contains three papers (Brysch-Herzberg et al, 2024;Etherington, Gomez-Gill, et al, 2023;Etherington, Wu, et al, 2023) that report new genome assemblies for S. japonicus and S. versatilis and revise the taxonomy of Schizosaccharomyces species.…”

“…The two independent studies by Etherington, Wu, et al (2023) and Brysch-Herzberg et al (2024) applied long-read genome sequencing to the type strain of S. japonicus and produced gapless genome assemblies. The assemblies fully recapitulate the three nuclear chromosomes but, remarkably, exceed the length of the reference S. japonicus genome by over 4 Mb (~30%).…”

Schizosaccharomyces versatilis represents a distinct evolutionary lineage of fission yeast

“…Advances in whole genome sequencing and assembly methods have made it possible to sequence and assemble the relatively small genomes of yeast species cheaply and quickly. All known species of fission yeast have now been sequenced (Brysch-Herzberg et al, 2024;Jia et al, 2023;Rhind et al, 2011;Wood et al, 2002). More recently, the availability of low-cost long-read sequencing combined with advances in genome assembly algorithms has allowed for chromosome-scale telomere-to-telomere sequencing to become achievable even for the most complex genomes (Belser et al, 2021;Nurk et al, 2022).…”