Yeast biodiversity in honey produced by stingless bees raised in the highlands of southern Brazil.

The physicochemical characteristics and yeasts diversity in honey samples from 17 species of stingless bees of the genera Nannotrigona, Melipona, Plebeia, Scraptotrigona, and Tetragonisca cultivated in Southern Brazil were determined. The sugar content, moisture, water activity, pH, reducing sugars/total sugar ratio, and total yeast population varied significantly among the honey from the different bee species. The highest yeast population was found in the Plebeia's honey samples and correlated with their high water-activity. Sixteen yeast species were identified based on the nuclear large subunit (26S) ribosomal RNA partial sequences. The genera Starmerella and Zygosaccharomyces were found predominant, with a high prevalence of Starmerella sp., S. etchellsii, and S. apicola. Some yeast species were only identified in honey samples from specific bee species indicating a close relationship between the yeasts and the insects. For the first time, Wickerhamomyces sydowiorum in honey is being reported. In general, the yeast species isolated from stingless bee honey samples demonstrated high osmotolerance and low sugar assimilation.

Activity of monoterpenoids on the in vitro growth of two Colletotrichum species and the mode of action on C. acutatum.

Essential oils and their main compounds, monoterpenoids, are considered as alternative control systems for phytopathogenic fungi, particularly those related to late diseases of fruits and vegetables, like anthracnose caused by Colletotrichum species. In this context, we studied the effect of twenty monoterpenoids on Colletotrichum fructicola and C. acutatum to elucidate their effectiveness and mechanisms of action. Thus, we analyzed mycelial growth and conidial inhibitory concentration, as well as the effect of selected monoterpenoids on membrane integrity and cell vitality, reactive oxygen species (ROS) accumulation, and mitochondrial membrane potential by flow cytometry. The results showed that oxygenated monoterpenoids (alcohols and aldehydes) exhibited higher antifungal activity than their corresponding hydrocarbons, esters, and cyclic counterparts. Indicating that OH- and O- radicals react with cellular components affecting fungal homeostasis. In this sense, selected monoterpenoids (citral, citronellol, geraniol, carvacrol, and thymol) inhibited conidial germination of C. acutatum in a dose-dependent manner. The inhibition of conidial germination is associated with a loss of membrane integrity, a decrease of cell metabolism, and a dose-dependent accumulation of ROS, which was non-directly associated with modifications on mitochondrial membrane potential. Membrane dysfunction and ROS accumulation may be responsible for the necrotic behavior induced by high monoterpenoids concentrations, and possible apoptotic response in sub dosages of these compounds.