DIFFERENCE COMPETITION BETWEEN WILD YEASTS ISOLATED WITH SOIL AND CANOPIES OF LARREA DIVARICADA AND BULNESIA RETAMA IN AN ARID ZONE OF SAN JUAN, ARGENTINA

ORO P. N. ; MATURANO Y. P.; NALLY M. C.; TORO M. E. ; VAZQUEZ F.

CORDOBA

Congreso; VI CONGRESO ARGENTINO DE MICROBIOLOGIA GENERAL; 2009

Arid ecosystems are dominated by shrubby vegetation, where soil properties are located in "islands of fertility". Among microorganisms associated to these fertility islands are yeasts. The distribution of yeasts in nature is not at random and those communities of species are defined by their habitat and the niche they occupy. Different yeasts belonging to various families and genera show a phenomenon known as killer, which implies a potential competition through the production of toxic glycoproteins. Ecological studies on this issue indicate that this phenomenon is a mechanism of interference competition, which involves the production of a toxin from yeasts in order to exclude others from their habitat. The objective of this study was to analyze competitive relationships (considering killer phenotype) between wild yeasts isolated from soil and canopies of Larrea divaricata and Bulnesia retama in a dry area of San Juan, Argentina, in two consecutive years. Samples were taken in sterile conditions from canopies of each shrub and in associated soils. Yeast isolations were from different culture media (Yeast Extract Peptone Dextrose and Yeast Malt), according to the topography of colonies. Taxonomic identification of yeasts was performed. Killer character was detected by cross-reactions between isolated yeasts. Data were analyzed by constructing contingency tables. Chi-square method was the most plausible to use (G2). From 96 yeasts isolated from the first sampling, 232 interactions were determined. The result was lower in the second sample. From 41 yeast isolations were found 98 interactions. From statistical data analysis it was inferred that in both samples the number of interactions depended on microsites from which yeasts were isolated (G2=56.22, p=0.0001, G2=31.22, p=0.0001). The species that presented the greatest number of interactions K/S (Killer/Sensitive) were Candida catenulata (65 K/S interactions) in the first sampling and Candida sake and Sporidiobolus johnsonii (18 and 19 interactions K/S respectively) in the second sampling. It was found that the number of interactions K/S were dependent of the species considered (G2=29.04, p=0.0001; G2=5.49, p=0.0043). It can be concluded that the number of interactions K/S depends on microsites which yeasts were isolated may be due to competition of microbial communities in habitats with low concentrations of available substrates, such as the study area that tends to produce separations in related ecological populations.