Taxonomy and phylogeny of the ascomycetous yeast genus Zygoascus, with proposal of Zygoascus meyerae sp. nov. and related anamorphic varieties Maudy Th. Smith, V. Robert, G. A. Poot, Wendy Epping and A. W. A. M. de Cock Correspondence Maudy Th. Smith smith@cbs.knaw.nl Centraalbureau voor Schimmelcultures, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands Physiological characters, mating compatibility, PCR-RAPD fingerprints, mol% G+C content, DNA–DNA relatedness, and large-subunit and internal transcribed spacer rRNA gene sequences of strains assigned to the genus Zygoascus were re-examined. On the basis of those data, and after phylogenetic analyses, an emendation of Zygoascus hellenicus (type material is a cross of CBS 6736 T 6CBS 5839 T ) is proposed, comprising two novel anamorphic varieties, Candida steatolytica var. steatolytica (CBS 6736 T ) and C. steatolytica var. inositophila (CBS 5839 T ). A novel teleomorphic species, Zygoascus meyerae sp. nov. (type material is a cross of CBS 4099 T 6CBS 7521 T ) is described, together with two novel anamorphic varieties corresponding to it, Candida hellenica var. hellenica (CBS 4099 T ) and C. hellenica var. acidophila (CBS 7115 T ). INTRODUCTION The monotypic genus Zygoascus was introduced in 1986 by Smith to accommodate the teleomorph state of three Candida species: Candida hellenica (Verona & Picci) D. S. King & S.-C. Jong, Candida inositophila Nakase and Candida steatolytica Yarrow. These species were all found to repre- sent mating types of a single species, with C. hellenica and C. inositophila representing one mating type, designated a, and C. steatolytica representing the opposite type, desig- nated a. C. inositophila and C. steatolytica were placed into synonymy with C. hellenica, since that name has priority, and the nomenclaturally independent teleomorph name Zygoascus hellenicus was modelled after the accepted anamorph name. In earlier studies, Meyer et al. (1984) reported that, of four strains previously identified as being representatives of C. steatolytica [Centraalbureau voor Schimmelcultures (CBS catalogues; CBS, 1972)], only one showed a DNA–DNA relatedness of 98 % with the type strain. Therefore, the remaining strains were excluded from this species and remained unclassified. Furthermore, Meyer et al. (1984) kept C. steatolytica and C. inositophila as separate taxa, because the DNA–DNA reassociation value between the type strains of these species was around 57 %, as deter- mined by the DNA filter reassociation technique (S. A. Meyer, personal communication), a value considered by Meyer to be low enough to keep the species apart. However, the observation of mating among the three unclassified isolates and the type strains of the three aforementioned species, resulting in asci with ascospores, was considered sufficient to conclude that they all belonged to the species Z. hellenicus (Smith, 1986). Accepting the presence of mating as an indicator of conspecificity, Meyer et al. (1998) excluded these three species from the list of purely anamorphic Candida species in a later revision of this genus. As these species concepts based on sexual compatibility and DNA–DNA relatedness values were discrepant and, as we had obtained some new and difficult-to-place Z. hellenicus- like isolates, we undertook a revision of this group. In this study, physiological characters and mating behaviour were studied, and genome-level differences were examined by means of PCR-randomly amplified polymorphic DNA (RAPD) analyses, DNA–DNA reassociation studies and sequencing of the D1/D2 domain of the large-subunit (LSU) rRNA gene, as well as the internal transcribed spacer (ITS) regions ITS1 and ITS2 and the intervening 5?8S rRNA gene. METHODS Cultures. In Table 1, 14 Zygoascus strains as well as the type strain of Pichia hangzhouana (Lu & Li, 1989) are listed, together with their respective origins and original identifications. P. hangzhouana was Abbreviations: ITS, internal transcribed spacer; LSU, large subunit. Published online ahead of print on 3 December 2004 as DOI 10.1099/ ijs.0.63277-0. The GenBank/EMBL/DDBJ accession numbers for the 26S and ITS rRNA gene sequences determined in this study are given in Table 1. 63277 G 2005 IUMS Printed in Great Britain 1353 International Journal of Systematic and Evolutionary Microbiology (2005), 55, 1353–1363 DOI 10.1099/ijs.0.63277-0