These ants have a specialized organ in their guts that breeds bacteria, allowing them to recycle waste into vital nutrients and thrive on a diet low in nitrogen – much like how some plants rely on root bacteria to fix nitrogen from the air. This setup not only supports the adult ants but also boosts the growth of their young, ensuring the whole colony’s success.
“It’s surprising how few clades and species have comparably detailed data on the nature and significance of microbial associations,” researchers write in the study.
In many animals, partnerships with microbes help overcome dietary shortages, such as by providing missing vitamins or breaking down tough foods. Ants, as one of the planet’s most dominant insects, often form such alliances, especially in groups that feed on plant-based materials poor in essential nutrients like amino acids. But how these symbioses work at the level of an entire colony, with its division of labor between workers and larvae, has remained largely unexplored.
Yi Hu and his colleagues examined four species of Tetraponera ants from the nigra-group, which live in trees across tropical regions and feed on sugary but nitrogen-scarce sources like honeydew from scale insects or nectar from plants. Using microscopes, they discovered a pouch-like organ at the junction of the midgut and hindgut in adult workers, connected to tubes that handle waste and oxygen. This pouch, absent in larvae and only forming during the pupal stage, is packed with rod-shaped bacteria visible under high magnification.
Genetic sequencing of the pouch contents showed that the bacteria are dominated by a single type called Tokpelaia, consistent across colonies and species. These microbes live almost exclusively in the pouch, though smaller numbers appear in the hindgut. The bacteria’s genomes reveal they can take up uric acid, a common waste product in insects, and break it down into usable forms, then use that nitrogen to build essential amino acids that ants cannot make on their own.
To test the partnership’s importance, the team created ant workers without symbionts by isolating pupae in sterile conditions. When these symbiont-free adults cared for larvae, the young ants grew more slowly, had lower survival rates, and emerged as smaller adults compared to those raised by normal workers. Over 90 days, pupation and emergence rates also dropped, showing that the symbiosis is key to colony health.
Feeding experiments confirmed the nutrient flow. When colonies received urea labeled with a heavy nitrogen isotope, symbiotic workers incorporated it into amino acids in their blood, including essentials like arginine and phenylalanine. Larvae raised by these workers showed even stronger enrichment in their tissues – more than twice that of the adults – but only if the symbionts were present. Without them, no such boost occurred.“Our findings indicate that the bacterial pouch – an unusual symbiotic organ that might be unique in Hymenoptera – enables an efficient nitrogen economy within the holobiont of T. nigra-group ant species,” researchers write in the study.
Citations
Y. Hu et al. Symbiotic solutions for colony nutrition: Conserved nitrogen recycling within the bacterial pouch of Tetraponera ants. Proceedings of the National Academy of Sciences. Published online October 28, 2025. DOI: 10.1073/pnas.2514882122
