A recent study suggests that the pheromones ants leave on their trail for communication may actually come from the bacteria living in their gut.
A particular species of ant called the leafcutters or Atta sexdens rubropilosa is found to be excreting a chemical called pyrazine, a key ingredient in pheromones.
Pheromones are similar to hormones in human beings, only that they work outside the body. These substances are secreted by ants' sweat gland to be left on the ground, which ants use as a tool for communication.
Biologists from the University of São Paulo in Brazil discovered that the scent trail is produced by Serratia marcescens, a type of bacteria that live and breed in the leafcutter ant's abdomen. The same bacterium was also found in other colonies examined for the study.
Researchers said this new information might also explain the symbiosis that takes place between bacteria and the human body.
Coauthor Mônica Tallarico Pupo, professor in the University of São Paulo's Ribeirão Preto School of Pharmaceutical Sciences (FCFRP-USP), said that while they have discovered that pyrazine is created by S. marcescens, it is unclear whether the bacteria is the source of pheromones or it only helped in the production of the chemical.
Initially, Pupo's team was investigating for microbes that protect the ants from parasitic bacteria. The researchers collected samples from ant colonies, including the queen, and isolated and cultured the bacteria from the ants.
"We found both pyrazines and bacteria in the ants' poison glands. We don't know for sure if their synthesis is shared: maybe the microorganism produces the aromatic compounds and the ants store them in their glands," Pupo said.
The researchers used a special fiber material typically used in culture plates. The samples were then analyzed by gas chromatography-mass spectrometry.
As it turned out, other ant species also use pyrazine for different purposes. Fire ants or Solenopsis invicta use it for signaling against enemies, while the Madagascan ant Eutetramorium mocquerysi) uses it as a trail sign.
Lead author Eduardo Afonso da Silva Junior explained that when the bacteria were cultured in the lab, it released a smell that is similar to that of the ants. Pupo added that Leucoagaricus gongylophorous, the fungal species on which the ants feed, thrive in the leaves they carry in their nests.
Interestingly, another type of pathogen is set out to kill this fungus without necessarily eating away the source of food.
Pupo said they will continue exploring possibilities by removing the bacteria from the ant's body and then observing if it will produce pyrazine by itself.
"The bacterial associates of ants in the tribe Attine have recently been exploited as a promising source of antibiotics thought to protect their hosts. The production of volatiles - critical class of molecules that guides ant behavior - by these bacteria, however, remain[s] largely unknown," the researchers wrote.
The study was published in the journal Scientific Reports.