ABSTRACT Soil microbiota is an important component of the forest biomes, playing important roles in the soil aggregation and cycling of nutrients. Among the soil microorganisms stand out the yeasts, which are unicellular fungi involved in important soil ecological processes. The Brazilian Atlantic Forest is one of the main biodiversity hotspots in the world, and the effect of altitudinal gradient on the distribution patterns of yeast species across this ecosystem has not yet been addressed. Thus, this study aimed to investigate the occurrence and distribution of yeast species in soils along an altitude gradient (404; 1,016; 1,658; and 2,124 m above the sea level) of Serra dos Órgãos National Park located at Rio de Janeiro State, Brazil. Yeast species were described using a culture-based method. Species identification was performed using the fungal barcode locus, the D1/D2 region of 26S rRNA, and the gene genealogy was used to access the intraspecific distribution of strains along the altitudinal gradient. We isolated and identified a total of 76 yeasts including ten species belonging to eight genera. Basidiomycetes predominated over ascomycetes. Saitozyma podzolica and Meyerozyma guilliermondii were isolated at all altitudes. The principal component analysis showed that 88 % of sample distribution is explained by soil properties. For S. podzolica, the genetic genealogy suggested that intraspecific distribution is likely related to similar altitudes. Overall, the species composition and soil properties were modified as altitude was increasing, being more heterogeneous and richness in high altitudes.

Os fungos rizoctonioides são os principais fungos micorrízicos de orquídeas. A caracterização morfológica e a análise de sequências conservadas do DNA total são as principais estratégias empregadas na identificação e no estudo da diversidade desses fungos. Contudo, fungos rizoctonioides fitopatogênicos têm sido caracterizados e identificados, de forma confiável e precisa, pela determinação da composição de seus ácidos graxos. Com o objetivo de avaliar a utilização da composição de ácidos graxos na caracterização e identificação de fungos rizoctonioides micorrízicos de orquídeas, três fungos Epulorhiza spp., micorrízicos de Epidendrum secundum, dois fungos não identificados, isolados de Epidendrum denticulatum, e um fungo fitopatogênico Ceratorhiza sp. AGC foram agrupados com base no perfil de seus ácidos graxos, utilizando as distâncias euclidiana e de Mahalanobis e o método UPGMA. Os dendrogramas gerados possibilitaram a distinção entre o isolado fitopatogênico de Ceratorhizasp. AGC e os fungos micorrízicos estudados. Os simbiontes de E. secundum foram distribuídos em dois clados: o primeiro contendo os isolados de Epulorhiza sp.1, e o segundo, o isolado de Epulorhiza sp.2. A similaridade entre os simbiontes de E. denticulatum e os fungos Epulorhizaspp. sugere a identificação desses simbiontes como Epulorhiza sp. Esses resultados foram semelhantes aos obtidos pela análise da região ITS (Internal Transcribed Spacer) do rDNA. O dendrograma construído a partir da distância de Mahalanobis apresentou melhor resolução, distinguindo claramente os clados descritos. A análise da composição de ácidos graxos mostrou ser uma ferramenta útil na caracterização e identificação dos fungos micorrízicos rizoctonioides estudados.

Rhizoctonia-like fungi are the main mycorrhizal fungi in orchid roots. Morphological characterization and analysis of conserved sequences of genomic DNA are frequently employed in the identification and study of fungi diversity. However, phytopathogenic Rhizoctonia-like fungi have been reliably and accurately characterized and identified through the examination of the fatty acid composition. To evaluate the efficacy of fatty acid composition in characterizing and identifying Rhizoctonia-like mycorrhizal fungi in orchids, three Epulorhiza spp. mycorrhizal fungi from Epidendrum secundum, two unidentified fungi isolated from Epidendrum denticulatum, and a phytopathogenic fungus, Ceratorhiza sp. AGC, were grouped based on the profile of their fatty acids, which was assessed by the Euclidian and Mahalanobis distances and the UPGMA method. Dendrograms distinguished the phytopathogenical isolate of Ceratorhiza sp. AGC from the mycorrhizal fungi studied. The symbionts of E. secundum were grouped into two clades, one containing Epulorhiza sp.1 isolates and the other the Epulorhiza sp.2 isolate. The similarity between the symbionts of E. denticulatum and Epulorhiza spp. fungi suggests that symbionts found in E. denticulatum may be identified as Epulorhiza. These results were corroborated by the analysis of the rDNA ITS region. The dendrogram constructed based on the Mahalanobis distance differentiated the clades most clearly. Fatty acid composition analysis proved to be a useful tool for characterizing and identifying Rhizoctonia-like mycorrhizal fungi.