The Hyphosphere of Leaf-Cutting Ant Cultivars Is Enriched with Helper Bacteria

Bacteria can live in a variety of interkingdom communities playing key ecological roles. The microbiome of leaf-cutting attine ant colonies are a remarkable example of such communities, as they support ants' metabolic processes and the maintenance of ant-fungus gardens. Studies on this topic have explored the bacterial community of the whole fungus garden, without discerning bacterial groups associated with the nutrient storage structures (gongylidia) of ant fungal cultivars. Here we studied bacteria isolated from the surface of gongylidia in the cultivars of Atta sexdens and Acromyrmex coronatus, to assess whether the bacterial community influences the biology of the fungus. A total of 10 bacterial strains were isolated from gongylidia (Bacillus sp., Lysinibacillus sp., Niallia sp., Staphylococcus sp., Paenibacillus sp., Pantoea sp., Staphylococcus sp., and one Actinobacteria). Some bacterial isolates increased gongylidia production and fungal biomass while others had inhibitory effects. Eight bacterial strains were confirmed to form biofilm-like structures on the fungal cultivar hyphae. They also showed auxiliary metabolic functions useful for the development of the fungal garden such as phosphate solubilization, siderophore production, cellulose and chitin degradation, and antifungal activity against antagonists of the fungal cultivar. Bacteria-bacteria interaction assays revealed heterogeneous behaviors including synergism and competition, which might contribute to regulate the community structure inside the garden. Our results suggest that bacteria and the ant fungal cultivar interact directly, across a continuum of positive and negative interactions within the community. These complex relationships could ultimately contribute to the stability of the ant-fungus mutualism.

Uncovering the Yeast Communities in Fungus-Growing Ant Colonies

Yeast-insect interactions are compelling models to study the evolution, ecology, and diversification of yeasts. Fungus-growing (attine) ants are prominent insects in the Neotropics that evolved an ancient fungiculture of basidiomycete fungi over 55-65 million years, supplying an environment for a hidden yeast diversity. Here we assessed the yeast diversity in the attine ant environment by thoroughly sampling fungus gardens across four out of five ant fungiculture systems: Acromyrmex coronatus and Mycetomoellerius tucumanus standing for leaf-cutting and higher-attine fungicultures, respectively; Apterostigma sp., Mycetophylax sp., and Mycocepurus goeldii as ants from the lower-attine fungiculture. Among the fungus gardens of all fungus-growing ants examined, we found taxonomically unique and diverse microbial yeast communities across the different fungicultures. Ascomycete yeasts were the core taxa in fungus garden samples, with Saccharomycetales as the most frequent order. The genera Aureobasidium, Candida, Papiliotrema, Starmerella, and Sugiyamaella had the highest incidence in fungus gardens. Despite the expected similarity within the same fungiculture system, colonies of the same ant species differed in community structure. Among Saccharomycotina yeasts, few were distinguishable as killer yeasts, with a classical inhibition pattern for the killer phenotype, differing from earlier observations in this environment, which should be further investigated. Yeast mycobiome in fungus gardens is distinct between colonies of the same fungiculture and each ant colony harbors a distinguished and unique yeast community. Fungus gardens of attine ants are emergent environments to study the diversity and ecology of yeasts associated with insects.

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.