Symbiosis, a diverse range of interactions between different species, has shaped life on earth: from the first eukaryote evolving as cooperation between several prokaryote elements, to the bacterial biofilms that define gut community of any organism. Colonies of advanced eusocial insects are second in complexity only to our own human societies, and among these the Latin American fungus-growing ants stand out because they have in common with human societies that they farm their own food. Because the fungus-growing ants have a very specialized diet, their gut bacterial communities are simpler than those of humans, making them an auspicious model system for gut microbiota studies. To enable humans to manipulate insect populations for the benefit of society, it will be crucial to better understand why and how symbiotic bacteria including gut microbiota are necessary for insect survival as these bacteria are believed to be a major reason for the overall abundance of both pest and beneficial insects in most terrestrial environments. The central aim of this project was to understand the nature of the symbiosis between leaf-cutting attine ants and their gut bacteria, the functional role of which was to a large extent unknown.