OCCURRENCE AND DIEL DISTRIBUTION OF YEASTS IN A PALEO-KARSTIC LAKE OFSOUTHEASTERN BRAZIL

The seasonal and diel distribution of yeasts was studied in tile paleo -karstic lake Lagoa Santa. The possible influence of environmental par ameters on tile total fungal counts and occurrence of yeast species wa s examined. The lake showed thermal and oxygen homogeneity in June, an d a stratification of temperature and oxygen in the water column durin g the period from September to March. The yeast species diversity decr eased with depth probably due to the oxydative profile of the predomin ant species that could limit their distribution to the highly oxygenat ed surface waters. The most frequent species were Cryptococcus flavus, Rhodotorula minuta, Trichosporon cutaneum, Tr. pullulans and Aureobas idium pullulans. The yeast counts and species diversity were higher du ring the fairly months of December and March, and lower in the dry sea son. Trichosporon cutaneum was predominant in the dry season, and it w as considered to be indigenous to the lake. The predominance of oxidat ive polytrophic yeasts and pigmented species suggested that the mycobi ota of the lake was probably carried from soils and foliar surfaces. T he yeast populations of Lagoa Santa lake would be formed by the consta nt efflux of transitory allochtonous species to die lake by rain and t he catchment basin.