Yeasts in the nests of the leaf-cutter ant Acromyrmex balzani in a Savanna biome: exploitation of community and metabolic diversity.

The leaf-cutter ant Acromyrmex balzani is responsible for causing important losses in reforestation areas, crops, and pastures, and is frequently found in the Brazilian savanna (Cerrado). So far, there is no information regarding the yeast communities that occur in their nests. Here, we evaluated the diversity, composition, and structure of yeast communities in both fungus gardens (FG) and external refuse dump (RD) of this ant species (Palmas, Tocantins, northern Brazil). A total of 720 yeasts were isolated, comprising 52 species distributed in 29 genera. The RDs have significantly richer and more diverse yeast communities than the fungus gardens, regardless of the season and the level of preservation in the area. The isolates produced a wide range of carbon polymer-degrading enzymes and were able to assimilate carbon-sources present in plant materials. We observed a different proportion of enzyme-producers and carbon-assimilation found in external refuse dump and fungus gardens from preserved and disturbed areas, suggesting that this interaction may vary depending on the environmental conditions. A. balzani nests in the savanna biome are a hotspot of yeast species with ecological, clinical, and biotechnological implications.

Endophytic Actinobacteria from the Brazilian Medicinal Plant Lychnophora ericoides Mart. and the Biological Potential of Their Secondary Metabolites.

Endophytic actinobacteria from the Brazilian medicinal plant Lychnophora ericoides were isolated for the first time, and the biological potential of their secondary metabolites was evaluated. A phylogenic analysis of isolated actinobacteria was accomplished with 16S rRNA gene sequencing, and the predominance of the genus Streptomyces was observed. All strains were cultured on solid rice medium, and ethanol extracts were evaluated with antimicrobial and cytotoxic assays against cancer cell lines. As a result, 92% of the extracts showed a high or moderate activity against at least one pathogenic microbial strain or cancer cell line. Based on the biological and chemical analyses of crude extracts, three endophytic strains were selected for further investigation of their chemical profiles. Sixteen compounds were isolated, and 3-hydroxy-4-methoxybenzamide (9) and 2,3-dihydro-2,2-dimethyl-4(1H)-quinazolinone (15) are reported as natural products for the first time in this study. The biological activity of the pure compounds was also assessed. Compound 15 displayed potent cytotoxic activity against all four tested cancer cell lines. Nocardamine (2) was only moderately active against two cancer cell lines but showed strong activity against Trypanosoma cruzi. Our results show that endophytic actinobacteria from L. ericoides are a promising source of bioactive compounds.

Yeasts found on an ephemeral reproductive caste of the leaf-cutting ant Atta sexdens rubropilosa.

Winged males of leaf-cutting ants are considered an ephemeral reproductive caste only produced before the mating flight season. Although much is known about the yeast diversity found in fungus gardens of attine ants, no study has focused on the yeasts associated with males of leaf-cutting ants. Here, we surveyed the yeasts on the integuments of males of Atta sexdens rubropilosa and assessed their potential role in the attine ant-microbe symbiosis. Using culture-dependent techniques, we found yeasts to be abundant on the integuments of males (54.5 %, n = 200 alates). A total of 242 yeast strains were obtained representing six orders, ten genera and 25 species. Strains of Aureobasidium, Cryptococcus, Hannaella and Rhodotorula were prevalent on the integuments and likely originated from the fungus garden of the parental nest or from the soil. The majority of strains (87.1 %) produced at least one of the evaluated enzymes: pectinase, polygalacturonase, cellulase, xylanase, ligninases and lipase. Aureobasidium pullulans accounted for the highest number of strains that produced all enzymes. In addition, yeasts showed the ability to assimilate the resulting oligosaccharides, supporting observations of other studies that yeasts may be involved in the plant biomass metabolism in the fungus gardens. Because winged males harbor several yeasts with putative functional roles, these fungi may take part and be beneficial in the microbial consortia of the new incipient nest.

Further evidences of an emerging stingless bee-yeast symbiosis.

Symbiotic interactions between microorganisms and social insects have been described as crucial for the maintenance of these multitrophic systems, as observed for the stingless bee Scaptotrigona depilis and the yeast Zygosaccharomyces sp. SDBC30G1. The larvae of S. depilis ingest fungal filaments of Zygosaccharomyces sp. SDBC30G1 to obtain ergosterol, which is the precursor for the biosynthesis of ecdysteroids that modulate insect metamorphosis. In this work, we find a similar insect-microbe interaction in other species of stingless bees. We analyzed brood cell samples from 19 species of stingless bees collected in Brazil. The osmophilic yeast Zygosaccharomyces spp. was isolated from eight bee species, namely Scaptotrigona bipunctata, S. postica, S. tubiba, Tetragona clavipes, Melipona quadrifasciata, M. fasciculata, M. bicolor, and Partamona helleri. These yeasts form pseudohyphae and also accumulate ergosterol in lipid droplets, similar to the pattern observed for S. depilis. The phylogenetic analyses including various Zygosaccharomyces revealed that strains isolated from the brood cells formed a branch separated from the previously described Zygosaccharomyces species, suggesting that they are new species of this genus and reinforcing the symbiotic interaction with the host insects.