Diversity of phylloplane yeasts and yeast likefungi of high altitude trees in Patagonia (Argentina) and synthesis of photoprotective compounds

LIBKIND, DIEGO; MUÑOZ, MARIO IVÁN; MOLINÉ, MARTÍN

Sapporo

Congreso; XIII International Congress of Mycology; 2011

IUMS (International Union of Microbiological Societies)

Microorganisms inhabiting leaves surfaces of mountain trees are exposed to extreme environmental conditions, due to the combined effect of high desiccation, low temperature and increased solar ultraviolet radiation (UVR). UVR, particularly UV-B, is damaging to microorganisms of the phyllosphere and a common strategy to increase UV tolerance is the synthesis of photoprotective compounds that act as antioxidant and/or UV sunscreens. In this work we studied the phylloplane yeast and yeast-like fungi (YLF) from the leaves of Nothofagus pumilio, an endemic deciduous species and the main species of the high altitude tree-line forests of the Andes, and screened for photoprotective metabolites (carotenoids, melanins and mycosporines). Fungi from sun-covered and exposed N. pumilio leaves in the Nahuel Huapi National Park, Patagonia, Argentina, were counted and representative isolates were studied. A total of 128 isolates were assigned to 40 different species (16 were undescribed taxa) by rDNA sequencing, 65% of which were yeasts mainly of the Basidiomycota. Total fungal counts rarely exceeded 103 CFU/m2, considerably lower than those generally reported for phylloplane. Total CFU counts were lower in exposed leaves than in covered ones, indicating a significant limiting effect of UVR to the phyllosphere fungal community. YLF were generally more abundant than yeasts, especially in covered leaves due to the prevalence of Aurebasidium pullulans. A. pullulans together with the ascomycetous yeasts were almost absent in exposed leaves suggesting susceptibility to UVR. 80% of the isolates produced at least one type of photoprotective compound. Mycosporine synthesis was the most frequent both in yeasts and YLF followed by carotenoids in yeasts or melanin in YLF. An interesting fungal diversity was found in N. pumilio phyllosphere, with many undescribed taxa and frequent occurrence of photoprotection mechanisms as an adaptation against the detrimental effect of UVR.