You are what your fungus eats: Diet shapes the microbial garden of a fungus-growing ant

Background Fungus-growing ants maintain an ectosymbiotic microbial garden, an intertwined mesh of fungal symbiont hyphae growing through plant cells. In this environment, plant decay progresses along a longitudinal continuum, providing a scaffold for a microbiota that colonizes both the hyphae and the plant substrate. In this study, we investigate how different plant diets influence the garden chemical profile, and whether the microbiota respond to these dietary changes. Colonies of Atta sexdens were provided with four different dietary regimens over 56 days, each varying in fiber composition and nutritional content. We then analyzed the lignocellulosic profile of the garden, along with the taxonomic composition and spatial distribution of the microbiota. Results We observed a spatiotemporal assembly of the microbiota throughout the lignocellulose decay continuum, with different garden regions exhibiting distinct patterns of bacterial and fungal richness, abundance, and diversity. ¹³ C ssNMR revealed that fruits and cereals led to an increase in hemicelluloses, particularly those related to xylan, across various garden regions. Metabarcoding data indicated that dietary changes influenced the microbial composition, although we also detected some microbes that flexibly adapted to distinct diets. Otherwise, certain genera were more prevalent in leaf-based diets, while others were favored in fruit-based diets. Some microbes thrive when exposed to a mix of plant fibers with varying degrees of recalcitrance. The spatial distribution of the microbiota also varied according to the diet, as indicated by SEM analysis. Notably, fruits and cereals correlated with biofilm spreading and altered fungal crop development. Our findings suggest that diet, particularly composed exclusively of fruits and cereals, has a significant impact on colony health and functioning. Conclusions Distinct plant substrates, provided through different diets, shaped the garden microhabitats, affecting the system across several intercorrelated dimensions: the garden’s lignocellulosic profile, microbiota spatial distribution, taxonomic composition, and the colony health. Our findings highlight the pivotal role of diet in shaping the microbiota by defining the nutritional landscape, ultimately determining whether ant colonies function optimally and remain healthy.