A comparison of yeast communities found in necrotic tissue of cladodes and fruits ofOpuntia stricta on Islands in the Caribbean Sea and where introduced into Australia

Metschnikowia lochheadii and Metschnikowia drosophilae, two new yeast species isolated from insects associated with flowers

Two new haplontic heterothallic species of Metschnikowia were isolated from floricolous insects and flowers. Metschnikowia lochheadii was recovered from insects found in various flowers on the Hawaiian Islands of Kauai and Maui, and from Conotelus sp. (Coleoptera: Nitidulidae) in northwestern Guanacaste Province, Costa Rica. The morphology, physiology, and sexual cycle are typical of the large-spored Metschnikowia species, and the partial ribosomal DNA large subunit (D1D2) sequences suggest that the new species is most closely related to Candida ipomoeae. Metschnikowia lochheadii is nearly indistinguishable from its ascogenous relatives and conjugates freely with Metschnikowia continentalis, forming sterile asci. It also exhibits asymmetric mating with Metschnikowia hawaiiensis. Metschnikowia drosophilae was found in morning glory (Ipomoea sp.) flowers and associated Drosophila bromeliae on Grand Cayman Island. Its nutritional profile is atypical of the genus, being the only species that does not utilize sucrose or maltose as carbon sources, and one of the few that does not utilize melezitose. D1D2 sequences show that Metschnikowia drosophilae is a sister species to Candida torresii, to which it bears considerable similarity in nutritional profile. The type cultures are: Metschnikowia lochheadii, strains UWO(PS)00-133.2 = CBS 8807 (h+, holotype) UWO(PS)99-661.1 = CBS 8808 (h-, isotype); and Metschnikowia drosophilae, strains UWO(PS)83-1135.3 = CBS 8809 (h+, holotype) and UWO(PS)83-1143.1 = CBS 8810 (h-, isotype).

Ribosomal DNA, species structure, and biogeography of the cactophilic yeast Clavispora opuntiae

The ribosomal DNA of the cactophilic yeast species Clavispora opuntiae was studied in order to clarify the global distribution of the yeast. Over 500 strains, including isolates from several new localities worldwide, were characterized by rDNA restriction mapping. An unusual restriction pattern previously encountered only in one strain, from Conception Island in the Bahamas, was found in several Brazilian isolates. Sequences of the D1/D2 and D7/D8 divergent domains of the large subunit (LSU) and of the intergenic spacers (IGS) confirmed that these strains represent a genetically distinct variety of Clavispora opuntiae. This divergence had previously been hypothesized on the basis of reduced genetic recombination in inter-varietal crosses and the presence of a polymorphic ApaI restriction site located in the LSU. The exact position of the ApaI site in the D8 divergent domain and the nature of the variation that it reveals were determined. The complete sequences of 12 intergenic spacers clarified the significance of the species-wide variation uncovered by restriction mapping. Most of the polymorphic sites occur in the IGS1 and IGS2 regions, on either side of the 5S gene, and the variation is largely due to differences in the numbers and the sequences of internal repeats. Two other polymorphic sites are located in the external transcribed spacer (ETS) region. The reliability of various sites as indicators of overall spacer sequence divergence differed from one case to another. Variety-specific probes were devised and used to screen 120 strains for the presence of recombinant rDNA spacers. Three strains gave ambiguous results, but these did not constitute evidence that inter-varietal recombination has taken place in nature. The hypothesis that the global movement of Clavispora opuntiae has been influenced by the worldwide biological control of prickly pear with Cactoblastis cactorum, a moth of Argentinian origin, has received additional support from the demonstration that Argentinian strains have rDNAs similar to those found where the moth has been introduced. A dramatic founder effect was identified in a yeast population collected in cacti (Maui, Hawaii) in a site where the moth had been recently introduced.

Yeast communities of the cactus Pilosocereus arrabidae and associated insects in the Sandy coastal plains of southeastern Brazil

The yeast communities from necrotic tissues, decaying flowers and fruits, and from larval feeding sites of the moth Sigelgaita sp. in the cactus Pilosocereus arrabidae were surveyed in three restinga ecosystems in Southeastern Brazil. Insects associated with these substrates were sampled to verify the vectoring of yeasts. The cactus Pilosocereus arrabidae was shown to have four different yeast communities associated with it. Necrotic stems had a diverse yeast community with the prevalent species Pichia barkeri, Candida sonorensis, Pichia cactophila, Geotrichum sp., Myxozyma mucilagina and Sporopachydermia sp. A, representing about 80% of the total isolates. Pichia sp. A and a Candida domercqii-like species represented more than 90% of the yeast isolates from decaying flowers. Fruits had a heterogeneous yeast community with typical fruit yeasts of the genus Kloeckera, basidiomicetous anamorphs of the genus Cryptococcus, the black yeast Aureobasidium pullulans, Pichia sp. A, a Candida domercqii-like species, and some cactophilic yeasts, especially Clavispora opuntiae. The feeding site of Sigelgaita sp. larvae had Clavispora opuntiae as the prevalent species. Insect vectors are suggested as one the most important factors influencing the composition of these yeast communities.