Symbiotic solutions for colony nutrition: conserved nitrogen recycling within the bacterial pouch of Tetraponera ants

Microbial symbioses are fundamental to the nutrition of many animal groups, yet the mechanisms of nutrient provisioning remain poorly understood -- even in social insects, a diverse clade whose global ecological dominance and sophisticated caste systems make them disproportionately well-studied models for symbiosis research. Here, we investigate the functional significance of a specialized and unusual symbiotic organ-- the bacterial pouch--in four ant species within the Tetraponera nigra-group, focusing on the symbionts roles in nitrogen recycling and colony fitness. Bacterial pouch houses a microbial community consistently dominated by the core bacterial symbiont Tokpelaia. Metagenomic sequencing and targeted {superscript 1}N-labeled urea feeding experiments demonstrate that these symbionts assimilate nitrogen from urea into amino acids, transferring them to adult workers and developing larvae that incorporate recycled nitrogen into their tissues. Disruption of this nitrogen-recycling symbiosis severely impairs larval growth and overall colony fitness. Our study highlights the critical role of the bacterial pouch in sustaining colony fitness in nitrogen-limited environments, providing new insights into the pivotal role of microbial symbioses in the ecological success of social insects.