Bacterial microbiota associated with the leaf-cutting ant Atta cephalotes (Hymenoptera: Myrmicinae): Dynamics during development and potential role in defence

The biological complexity of leaf-cutting ants is determined in part by both positive and negative associations with microorganisms. These ants constantly face microorganisms that can compromise workers’ survival and the integrity of their symbiont fungus. The ability to produce antimicrobial compounds within the colony, both by the workers and by associated microorganisms, is an adaptive response that protects against these natural enemies. Atta cephalotes (Linnaeus, 1758) is an ecologically successful species with a great capacity to overcome pathogenic microorganisms. In contrast to the Acromyrmex genus, the evidence suggests that it does not maintain an association with antibiotic-producing actinobacteria raising the question of whether this species maintains associations with bacterial communities that can potentially protect the colony against prejudicial microorganisms. In this direction, the diversity and composition of the culturable bacterial microbiota associated with A. cephalotes developmental stages were evaluated, as well as their potential to inhibit the growth of the entomopathogenic fungus Metarhizium anisopliae and the mycoparasite Trichoderma sp. Six nests were collected, of which a total of 900 larvae, 900 pupae and 900 adult workers were analysed. Culture-dependent and molecular methods were used to identify the strains to genus level. To determine differences in bacterial composition in the development stages, analysis of the contribution to dissimilarity (SIMPER) were performed. Seventy-seven strains corresponding to 18 genera were documented. Acinetobacter was the dominant one. On the other hand, Acinetobacter, Bacillus, Enterobacter, Serratia and Microbacterium were maintained from the larval to the adult stage. Furthermore, except for Acinetobacter, different strains of these bacterial groups significantly inhibited pathogenic fungi growth. The results suggest the existence of a persistent association of A. cephalotes with strains of these bacterial genera and a potential role in defence at the collective level.