Bacteria on Fungus Farming Ants Produce Antibiotics

Biological Strategy

Leafcutter ants

Natalie Chen

Image: Egor Kamelev / Pexels / Free non-commercial use

Biological Control of Populations, Pests, Diseases

An ecosystem must prevent overpopulation of any given species within it, as well as the spread of pests and diseases, to allow organisms to survive without threatening extermination of other organisms or ecosystems. To control pests and diseases, living systems use such strategies as developing antibodies and killing or repelling pests or disease-causing organisms. Ecosystems have checks and balances to maintain populations, pests, and diseases. For example, in a lake, a balance of predators, prey, and nutrients is crucial for proper functioning of the ecosystem. Predatory fish keep down the numbers of smaller prey fish, which in turn keep populations of algae-eating zooplankton in check. When the levels of any of these organisms change, the change can disrupt the health of the entire ecosystem.

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Manage Disturbance in a Community

When environmental conditions change, they can disrupt an ecosystem’s equilibrium. Excessive rain can cause flooding and drought can cause forest fires. An ecosystem must be resilient to such disturbances. Disturbances are unpredictable in location, size, and intensity, so ecosystems must be able to regrow and must have a variety of duplicate forms, processes, or systems that are dispersed in location. For example, a forest ecosystem can recover from fire because diverse organisms play different roles in different ways and in different locations. Many organisms can resprout or grow from seeds triggered by fire, and their dispersed distribution ensures that an entire population isn’t decimated. Though the recovered ecosystem may look totally different from the pre-fire one, the ecosystem as a whole remains healthy.

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Cooperate/Compete Between Different Species

From parasitism to mutualisms, there are endless interactions between organisms in nature. Interactions between species that lead to a negative outcome for one species are known as competition. Cooperation occurs when organisms work together for the benefit of each organism or species. While competition often occurs over resources or mates, the more biologists have begun to look for examples of cooperation in nature, the more they have found. For example, around 90% of plants have a beneficial partnership with fungi. Fungi provide the plant with nutrients such as nitrogen and phosphorus, in exchange for sugars from the plant.

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Protect From Microbes

In living systems, microbes play important roles, such as breaking down organic matter and maintaining personal and system health. But they also pose threats. Bacteria can be pathogens that cause diseases. Some bacteria create colonies called biofilms that can coat surfaces, reducing their effectiveness–for example, inhibiting a leaf’s ability to photosynthesize. Living systems must have strategies for protecting from microbes that cause disease or become so numerous that they create an imbalance in the system. At the same time, living systems must continue living in harmony with other microbes. Some living systems kill microbes. Others repel without killing to reduce the chances that microbes will adapt to the lethal strategy and become resistant to it. For example, some pea seedlings exude a chemical that inhibits biofilm buildup.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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

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.

Where Are the Ants Carrying All Those Leaves?

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.

Image: Alex Wild, for the University of Texas "Insects Unlocked" project. / Public Domain - No restrictions

The fungal nest of a leafcutter ant colony.

Last Updated July 1, 2020

References

“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 Evolution | 26/09/2019 | Ayush Pathak, Steve Kett, Massimiliano Marvasi

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