Leveduras vetorizadas por abelhas sem ferrão em áreas de cerrado no estado do Tocantins, Brasil

Abstract

There are evidences for a mutualistic interaction between yeasts and stingless bees, in which bees vector yeasts that serve as food item or modify the products of the nest. Various studies report the occurrence of species of the generea Candida e Starmerella associated with nests of different meliponini. In this study we identified the yeast species vectored by Frieseomellita varia, Scaptorigona polysticta, Sacaptorigona postica, Tetragonisca angustula angustula, Melipona compressipes manaoensis and Melipona scutellaris in areas of Cerrado, and we made a funtional analysis of the yeasts associated with Scaptorigona postica. Sampling was done between the years 2006 and 2015 in Tocantins State, Northern Brasil, and the collector bees were captured iin the nest entrance with sterile bags and put to walk on agar platescontaining YMA. Yeast isolates were identified by molecular methods using DNA extraction, PCR fingerprinting with primer EI-1 and sequencing of D1/D2 region of the gene 26S rDNA uing primers NL-1 and NL-4 of representative strains. Functional characters were tested as carbohydrate assimilation, osmotolerance and acid tolerance, and resistance to 37°C and 40°C for yeasts isolated from Scaptorigona postica. Among all stingless bees, 62 yeast species belonging to 18 genera of Ascomycota and six Basidiomycota were identified, with a higher frequency ofTorulaspora delbrueckii, Candida apicola, Pichia membranifaciens, Pichia kluyveri and Starmerella meliponinorum that represented 41% of the strains. Among these, C. apicola and S. meliponinorum are frequent in stingless bees, and the others are commonly isolated from sugary substrates, indicating that the bees vector yeasts from the enviroments where they collect nectar and pollen. Significant differences in the yeast composition occur between Meliponini and trigonini, indicating different strategies of visitation in the substrates colonized by yeasts. Also each bee species carries different yeast communities, indicating a selective and different collecting habit. Functional characters of 52 yeasts isolated from S. postica revealed that most assimilate simple sugars galactose, maltose, celobiose, and trealose, bu only ¼ of them assimilate sucrose and xylosis. Assimilation of starch and mellibiose was uncommon. Ethanol was assimilated by 36,53% of the yeasts but acetona, metanol and isopropanol were less frequently assimilated. Most yeasts was fermentative, osmophillic and resistant to acetic acid which indicates an adaptation to high sugar concentrations and the fermentative environment.