Biomedical subjects

Marc André Lachance

Publications and source records attributed to Marc André Lachance.

5 recordsLinked to original sources

PubMed2003

Ascospores of large-spored Metschnikowia species are genuine meiotic products of these yeasts.

The asci of Metschnikowia species normally contain two ascospores (never more), raising the question of whether these spores are true meiotic products. We investigated this problem by crossing genetically-marked strains of the haploid, heterothallic taxa Metschnikowia hawaiiensis, Metschnikowia continentalis var. continentalis, and M. continentalis var. borealis. Asci were dissected and the segregation patterns for various phenotypes analyzed. In all cases (n = 47) both mating types (h+ and h-) were recovered in pairs of sister spores, casting further uncertainty as to whether normal meiosis takes place. However, the segregation patterns for cycloheximide resistance and several auxotrophic markers were random, suggesting that normal meiosis indeed occurs. To explain the lack of second-division segregation of mating types, we concluded that crossing-over does not occur between the mating-type locus and the centromere, and that meiosis I is tied to spore formation, which explains why the number of spores is limited to two. The latter assumption was also supported by fluorescence microscopy. The second meiotic division takes place inside the spores and is followed by the resorption of two nuclei, one in each spore.

Crosses, Genetic↗

PubMed2003

The origin of the cactus-yeast community.

The yeast community found in decaying cactus stems and cladodes is stable in terms of species membership and is similar in composition over space and time. The ecological origins of the three core and four common species in the assemblage were inferred by mapping yeast habitats onto a phylogeny of yeasts reconstructed from rDNA sequences. The members of the community belong to distinct clades and consequently have independent origins. The inferred evolutionary pathways of the taxa originate in either tree-flux or decaying fruit habitats and lead to decaying Opuntia cladode and columnar stem habitats. The reasons for the polyphyletic origins of the cactus-yeast community could be due to unique aspects of cactus chemistry, environmental extremes, vector association and interactions among the members.

Cactaceae↗

PubMed2003

Geography and niche occupancy as determinants of yeast biodiversity: the yeast-insect-morning glory ecosystem of Kīpuka Puaulu, Hawai'i.

Biodiversity theory proposes two types of hypotheses to account for the species composition of a given community. The first encompasses geographic and historical factors. For example, local species richness is thought to be affected by area, proximity to large landmasses, dispersal mechanisms, and climatic history, collectively known as biogeography. The second type, termed niche occupancy rules, deals with the intrinsic properties of the species as they affect their interaction with the habitat and with other members of the community. The yeast-insect-morning glory ecosystem is a good model to explore biodiversity theory in ascomycetous yeasts. Here we focus on beetles that breed or feed in morning glories and a group of ascomycetous yeasts that are associated exclusively with them. Specifically, we analyse the community found in the vicinity of Kīpuka Puaulu, a small patch of disturbed but mature forest situated amidst lava flows on the island of Hawai'i. Major members of the yeast community include Metschnikowia hawaiiensis, Metschnikowia lochheadii, and the related asexual species Candida ipomoeae and Candida kipukae. These species are nearly indistinguishable from one another in terms of nutritional requirements and abilities, although their phylogenetic range is enormous. Their distribution, both global and local, is far from random. As Kīpuka Puaulu is an island within an island, the principles of island biogeography may be invoked to explain some aspects of its yeast species composition. M. lochheadii, C. ipomoeae, and the rare species Candida hawaiiana are recent introductions from the American continent and therefore exotic, whereas M. hawaiiensis and C. kipukae might be regarded as endemic, as they are yet to be isolated elsewhere. Vectoring by certain nitidulid beetles explains the long-range dispersal of these species. However, niche occupancy rules may account in part for the local spatial distribution of the yeasts within the island of Hawai'i and within the kīpuka itself. We have identified the maximum growth temperature as a potentially critical property of the fundamental niche of these yeasts.

Animals↗

PubMed2003

Yeast communities associated with stingless bees.

The yeast communities associated with the stingless bees Tetragonisca angustula, Melipona quadrifasciata and Frieseomelitta varia were studied. The bees T. angustula and F. varia showed a strong association with the yeast Starmerella meliponinorum. M. quadrifasciata more frequently carried a species related to Candida apicola, but also vectored low numbers of S. meliponinorum. Some of the yeasts isolated from adult bees were typical of species known to occur in flowers. Other yeast species found in adult bees were more typical of those found in the phylloplane. S. meliponinorum and the species in the C. apicola complex, also part of the Starmerella clade, may have a mutualistic relationship with the bees studied. Many yeasts in that group are often found in bees or substrates visited by bees, suggesting that a mutually beneficial interaction exists between them.

Animals↗

PubMed2003

Metschnikowia santaceciliae, Candida hawaiiana, and Candida kipukae, three new yeast species associated with insects of tropical morning glory.

A new haplontic heterothallic species of Metschnikowia and two related asexual yeast species were discovered in morning glory flowers and associated insects. Metschnikowia santaceciliae came from Conotelus (Coleoptera: Nitidulidae) and other insect species associated with flowers of Ipomoea indica (purple morph) in Costa Rica. Candida hawaiiana and Candida kipukae were found in I. indica (syn. I. acuminata) and its insects in Hawai'i, and the former was also isolated in a specimen of Conotelus collected on Merremia tuberosa (Convolvulaceae) in Costa Rica. The three species have nearly identical physiological profiles, typical of the genus Metschnikowia. The sequences of the D1/D2 domains of their large subunit ribosomal DNA confirm that the species belong to the Metschnikowia clade, even though they share a very low degree of inter-relatedness. M. santaceciliae is a sister species to Metschnikowia continentalis. C. kipukae is a basal member of the large-spored Metschnikowia subclade, and C. hawaiiana has a weak affinity to Metschnikowia agaves. Two of the three species appear to be endemic. The type cultures are: Metschnikowia santaceciliae, strains UWO(PS)01-517a1=CBS 9148=NRRL Y-27475 (h(+, holotype) and UWO(PS)01-520a1=CBS 9149=NRRL Y-27476 (h-, isotype); Candida hawaiiana, strain UWO(PS)91-698.3=CBS 9146=NRRL Y-27473; Candida kipukae, strain UWO(PS)00-669.2=CBS 9147=NRRL Y-27474.

Animals↗