Consequences of horizontal fungal exchange on the bacterial microbiome of fungus-gardening ants and their fungal symbionts

Higher attine ants have symbiotic relationships with the fungal cultivar they grow and the bacterial symbionts in their microbiomes. Among the so-called higher fungus-gardening ants, there are two broad groups of fungi. Most ants in the genus Trachymyrmex tend to grow so-called Clade B fungi, which are a group of undescribed Leucoagaricus species (referred to as ‘Clade B’) and there are the Clade A fungi (Leucoagaricus gongylophorus) that are typically grown by the leaf-cutting ants in the genera Acromyrmex and Atta. Previous work has shown that switching the cultivar grown by Trachymyrmex ants, from Clade B to Clade A fungus, creates an unstable symbiosis between the ants and their grown cultivar, resulting in a sudden decrease in the size of their fungal garden after a period of normal growth. One hypothesis for this instability is that the microbiome of fungus-gardening ants is specified for Clade B fungus and maintains the ant-fungus symbiosis. By switching the fungus, the microbiome is thought to undergo dysbiosis and cannot sustain the symbiotic relationship. In this study, we report the changes in the microbiome community of subcolonies of the fungus-gardening ant T. pomonae when their Clade B fungi are switched with a Clade A fungi from Acromyrmex versicolor.