Emendation of the Genus Issatchenkia Kudriavzev and Comparison of Species by Deoxyribonucleic Acid Reassociation, Mating Reaction, and Ascospore Ultrastructure

Abstract

The genus Issatchenkia Kudriavzev has been emended to include all nitratenegative, multilateral budding yeast species that form unconjugated persistent asci with roughened spheroidal ascospores and have Q-7 ubiquinone in the electron transport system. Pichia kudriauzeuii (Issatchenkia orientalis), Pichia terricola, Pichia scutulata var. scutulata, and Pichia scutulata var. exigua are assigned to this genus as Issatchenkia orientalis Kudriavzev exigua showed only 25% deoxyribonucleic acid complementarity, yet intervarietal matings formed viable ascospores. This is the lowest deoxyribonucleic acid relatedness ever shown between strains capable of genetic hybridization, and the implications of this finding are discussed. The genus Issatchenkia was described by Kudriavzev (11) in 1960 for yeasts which were isolated from fruit juices and berries and which had unconjugated asci and spheroidal ascospores. The single species originally included in the genus, Issatchenkia orientalis Kudriavzev Pichia terricola van der Walt and Pichia scutulata PhafT, Miller et Miranda are two other taxa phenotypically similar to P. kudriauzeuii. Scanning electron microscopy has shown that all three have warty ascospore walls (14,23), and in this respect, they differ from other roundspored species of Pichia, which have essentially smooth spore walls. Although these three species are similar in ascospore surface structure to species of Torulaspora (van der Walt [31] group 111, Saccharomyces species) and Debaryomyces (17), they do not form the asci with tapered projections that are associated with Torulaspora or exhibit the mother-daughter conjugation typical of Debaryomyces. Consequently, when ascus morphology and ascospore ultrastructure are considered, these species appear to represent a natural grouping that is different from other yeast genera, and we propose to place them in the genus Issatchenkia. On the basis of deoxyribonucleic acid (DNA) base sequence complementarity, mating reaction, and ascospore ultrastructure, we describe one new species, and several suggested perfect-imperfect relationships are verif'ied. Additionally, our multifaceted approach allowed an examination of species parameters that heretofore was not possible and suggested that, as is the case among some higher eucaryotes, the boundaries of individual yeast species may be less precisely definable than previously supposed. 503

The yeast genus Tortispora gen. nov., description of Tortispora ganteri sp. nov., Tortispora mauiana f.a., sp. nov., Tortispora agaves f.a., sp. nov., Tortispora sangerardonensis f.a., sp. nov., Tortispora cuajiniquilana f.a., sp. nov., Tortispora starmeri f.a., sp. nov. and Tortispora phaffii f.a., sp. nov., reassignment of Candida caseinolytica to Tortispora caseinolytica f.a., comb. nov., emendation of Botryozyma, and assignment of Botryozyma, Tortispora gen. nov. and Trigonopsis to the family Trigonops

“…NRRL Y-17796 represents the h + mating type, but did not form ascospores, and NRRL Y-48831 showed neither mating response nor ascospore formation. These results are not in conflict with our proposal that the strains represent separate species, as conjugation among closely related yeast species is not uncommon (Kurtzman et al, 1980;Naumov et al, 2000;Lachance et al, 2005). The responses to growth tests are given in Growth on YM agar: After 3 days on YM agar at 25 u C, the cells are ovoid, 1-1.562-3 mm and occur singly or in pairs (Fig.…”

Deoxyribonucleic Acid Base Sequence Relatedness among Members of the Yeast Genus Kluyveromyces

“…Van der Walt and Johannsen did report that some of their hybrids produced viable spores (38). Evidence for spore viability would be stronger, however, if quantitative data had been presented for all crosses rather than just a few and if spores had been isolated by micromanipulation (as was done by Kurtzman et al [21]) rather than by methods which may not have eliminated the vegetative cells. Douglas et al reported that a K .…”

A highly polymorphic degenerate microsatellite for molecular strain typing of Candida krusei The GenBank accession numbers for the sequences determined in this work are AF326279–AF326292.

“…Thus, our data support the reclassification of both sets of strains as a single species (Barnett et al, 2000). Some strains of I. orientalis have been shown to be able to sporulate, mate and exchange markers (Kurtzman & Smiley, 1976 ;Kurtzman et al, 1980). The ability to epidemiologically track a microorganism by molecular fingerprinting presupposes a primarily clonal, rather than sexual, mode of reproduction.…”