Bacteria growing on ants produce constantly changing antibiotics that invading fungi cannot develop resistance to.

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In nature, species work with each other to build long-lasting relationships. One example is the relationship between a  fungus-growing ant,  fungi, and bacteria. Fungus-growing ants grow a garden of fungi. The ants provide the fungi with food and an ideal habitat to grow, and in turn the fungus is a food source for the ants. Special bacteria living on the ants help protect the fungi from outside threats, such as other invading fungi. This three-way relationship is mutually beneficial. This means that two or more species work together to help each other and that the relationship has a positive benefit for everyone.

From time to time, bad fungi will try to invade the ant’s fungi garden. However, the ants cannot eat these fungi, so they would not benefit. Two species of bacteria live on the ant and receive food from the ant. In turn, they make a variety of antibiotic compounds that can stop the growth of these bad fungi. The bacteria can make a variety of different antibiotics by using different parts of their DNA. DNA provides instructions that tells the cells what kinds of compounds to make. The bacteria constantly use different parts of the instructions so that the antibiotic is always different. As a result, the bad fungi cannot develop a defense fast enough. To visualize this, imagine that the bad fungi need to produce a perfect key to open the gate to the ant’s fungi garden. To stop this from happening, the bacteria only need to make small changes to the key slot to stop the bad fungi from opening the gate. As a result, the bad fungi are rarely able to develop a defense against the antibiotics.

Humans can develop infections caused by bacteria. To treat the infections, doctors give antibiotics consisting of only one compound to kill the bacteria. Over time, the bacteria can learn to protect themselves and become resistant to the antibiotic. Therefore, humans could apply fungus-farming ant’s strategy by making small changes to the antibiotics that will make it more difficult for the bacteria to develop resistance.

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 “Fungus-growing ants (tribe: Attini)have cultivated specific fungi as food for 60 million years. Their coevolutionary interdependence is so refined that, for many attine species, their fungal cultivars are not found outside this symbiotic association. The fungi need specific microclimates and nutrition provided by the ants and, in turn, constitute the ants’ sole food source. Other fungi, of the genus Escovopsis, can invade the cultivated fungus and, because the ants rely entirely on cultivated fungus for food, this parasitism is detrimental to the ants.To counteract these parasitic fungi, ants have evolved multiple strategies. One is a tripartite mutualistic relationship, within which the ants host antimicrobial-producing bacteria on their bodies to protect their fungal cultivar. Many of these bacteria have coevolved with their hosts, producing antimicrobials to inhibit the parasitic fungi, while in return, the ants provide them with nutrition and a microclimate suitable for growth.” (Pathak et al. 2019: 974)

“In this coevolutionary arms race, novel bacterial antimicrobial compounds can be formed via novel gene cluster rearrangement or mutations. Novel compounds so generated achieve greater or lesser evolutionary success based upon the Escovopsis strain antimicrobial susceptibility… Humans use diverse antimicrobials, but they are structurally discrete compounds rather than the diverse range of subtle variants utilised by the ants and their mutualists. The humans’ strategy is also different; use of discrete antimicrobials as means of rapid pathogen elimination rather than one facet of a long-term strategy of progressive inhibition.” (Pathak et al. 2019: 976)

Journal article
Resisting Antimicrobial Resistance: Lessons from Fungus Farming Ants.Trends in Ecology and EvolutionSeptember 26, 2019
Ayush Pathak, Steve Kett, Massimiliano Marvasi

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