Candida coquimbonensis sp. nov., a link between Australian and Nearctic/Neotropical Phaffomyces.

A novel species of ascomycetous yeast, Candida coquimbonensis sp. nov., from the necrotic tissue of cacti in Chile and Australia is described. C. coquimbonensis sp. nov. is closely related and phenotypically similar to Phaffomyces opuntiae. There is no overlap in the geographical distribution between C. coquimbonensis and any species in the Phaffomyces clade. However, this is the first member of the clade to be collected in both native (Chile) and non-native (Australia) cactus habitats. The type strain of C. coquimbonensis sp. nov. is TSU 00-206.4B(T) ( = CBS 12348(T) = USCFST 12-103(T)).

The vectoring of cactophilic yeasts by Drosophila.

At two locations in the Sonoran Desert, yeasts were sampled from species of Drosophila, the flies' cactus hosts, and other neighboring sources of cactophilic yeasts to determine the relation between the yeasts vectored by the fly and the yeasts found in their breeding sites. D. mojavensis, D. nigrospiracula, and D. mettleri vectored yeast assemblages significantly more similar to the yeast species found on the rot from which the flies were collected than to the yeasts found on other rots from the flies host cactus or other rotting cactus at the same site. Rots with Drosophila had fewer yeast species than those without flies, suggesting that flies were associated with younger rots. Rots with flies and the Drosophila also had more yeast species with the capability to produce ethyl acetate than rots without flies. The results support the contention that cactophilic Drosophila feed on a subset of the yeasts available in an area, and may act to maintain differences among the yeast communities found on different species of cactus.

Yeast communities from host plants and associated Drosophila in southern arizona: new isolations and analysis of the relative importance of hosts and vectors on comunity composition.

The yeast communities from slime fluxes of three deciduous trees (Prosopis juliflora, Populus fremontii and Quercus emoryi) and the necroses of two cacti (Opuntia phaeacantha and Carnegiea gigantea) were surveyed in the region of Tucson, Arizona. In addition, the yeasts carried by dipterans associated with the fluxes or necroses (Drosophila carbonaria, D. brooksae, D. nigrospiracula, D. mettleri, and Aulacigaster leucopeza) were sampled. The results indicate that each host sampled had a distinct community of yeasts associated with it. The dipterans, which can act as vectors of the yeasts, deposited yeasts from other sources in addition to those found on their associated hosts. It is argued that host plant physiology is relatively more important than the activity of the vector in determining yeast community composition. Furthermore, the average number of yeast species per flux or necrosis is not different from the average number of yeast species per fly. It is hypothesized that the vector may affect the number of species per individual flux or not, and that the number is lower than the rot or necrosis could potentially support.

Pichia insulana sp. nov., a novel cactophilic yeast from the Caribbean.

A novel species of ascomycetous yeast, Pichia insulana sp. nov., is described from necrotic tissue of columnar cacti on Caribbean islands. P. insulana is closely related to and phenotypically very similar to Pichia cactophila and Pichia pseudocactophila. There are few distinctions between these taxa besides spore type, host preference and locality. Sporogenous strains of P. insulana that produce asci with four hat-shaped spores have been found only on Curaçao, whereas there was no evidence of sporogenous P. cactophila from that island. In addition, sequences of the D1/D2 fragment of the large-subunit rDNA from 12 Curaçao strains showed consistent differences from the sequences of the type strains of P. cactophila and P. pseudocactophila. The type strain of P. insulana is TSU00-106.5(T) (=CBS 11169(T) =UCD-FST 09-160(T)).

QUANTUM AND CONTINUOUS EVOLUTION OF DNA BASE COMPOSITION IN THE YEAST GENUS PICHIA.

This paper investigates the noncontinuous nature and evolution of the base composition of nuclear DNA (expressed as mol% guanine + cytosine) in species of the yeast genus Pichia (sensu Kurtzman, 1984b). The pattern of change in the G + C contents in species of this genus, which range from about 27 to 52 mol%, was evaluated. When specifically those species of Pichia were analyzed that have evolved in necroses of cactus species and associated Drosophila, a periodic change in the G + C contents of approximately 3.0-3.2 mol% was detected by a "bootstrapping" method, Fourier analysis, and a nonlinear trigonometric model. Pichia species occurring in exudates of broad-leaved deciduous trees or associated Drosophila and substrates such as soil and water ("other") showed a periodicity of 2.5-2.6 mol%, whereas species associated with conifers and associated bark beetles showed no significant periodicity. Periodicity in the most recent association (cactus and resident Drosophila) as compared to the lack of periodicity in the oldest association (conifer-beetle) may indicate mixed evolutionary processes. Low mol% G + C values appear more frequently in the relatively recent cactus and Drosophila-associated yeast species. In addition, low mol% G + C species do not display the ancestral bud-meiosis mode of sexual reproduction which occurs frequently in medium to high mol% G + C yeasts. It was found that the mol% G + C content of the Drosophila- and cactus-associated Pichia species is positively correlated with the number of compounds fermented or respired by these yeast species. Possible reasons for the periodic changes in mol% G + C content accompanying speciation include aneuploidy, allopolyploidy, the presence of nuclear plasmids, and regular differences in moderately repetitive portions of DNA. Since significant DNA complementarity is virtually limited to species within a relatively narrow G + C group, this suggests that there are at least two processes which alter the G + C content between species, one saltational and one continuous.

Correlations among measures of phenotypic and genetic variation within an oligotrophic asexual yeast, Candida sonorensis, collected from Opuntia.

Many descriptions of yeast species are based on a limited number of strains collected at one time from a single locale. Often, little is known of phenotypic or genotypic variation and covariation within species. We compare 36 strains of an asexual cactophilic yeast, Candida sonorensis, collected from Opuntia cacti. Comparisons were based on geographical distances between collection locales, responses to physiological assimilation and stress tests, random amplified polymorphic DNA (RAPD) profiles, partial Lage Subunit (LSU) rDNA sequences, relative DNA-DNA hybridization values, and electrokaryotypes. There was significant variation among strains in all types of data collected. Comparisons among the different data types found significant positive associations between RAPD profiles, geographical distances, physiologies, reassociation values, and electrokaryotypes. No significant associations were found between rDNA sequences and any other type of variation measured. Based on RAPD, reassociation, electrokaryotype, and physiological data, the 36 strains could be divided into two groups: those collected in West Texas (nine strains) and all others. RAPD data indicated that 10 (of 12) Australian strains also formed a distinct clade. The taxonomic and phylogenetic status of these clades is discussed. Evidence that new genotypes can sweep through large geographic areas is also discussed.

Evidence for multiple interspecific hybridization in Saccharomyces sensu stricto species.

Fluorescent amplified fragment length polymorphism analysis demonstrates a high level of gene exchange between Saccharomyces sensu stricto species, with some strains having undergone multiple interspecific hybridization events with subsequent changes in genome complexity. Two lager strains were shown to be hybrids between Saccharomyces cerevisiae and the alloploid species Saccharomyces pastorianus. The genome structure of CBS 380(T), the type strain of Saccharomyces bayanus, is also consistent with S. pastorianus gene transfer. The results indicate that the cider yeast, CID1, possesses nuclear DNA from three separate species. Mating experiments show that there are no barriers to interspecific conjugation of haploid cells. Furthermore, the allopolyploid strains were able to undergo further hybridizations with other Saccharomyces sensu stricto yeasts. These results demonstrate that introgression between the Saccharomyces sensu stricto species is likely.