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Fungus-farming ants use antibiotic combo to kill off weeds

Scientists from China and the UK have discovered that a leaf-cutting ant, Acromyrmex octospinosus, uses a cocktail of antibiotics to keep its fungus gardens neat. Among these antibiotics, which are produced by bacteria living on the ants, is a novel compound that could be used...

Scientists from China and the UK have discovered that a leaf-cutting ant, Acromyrmex octospinosus, uses a cocktail of antibiotics to keep its fungus gardens neat. Among these antibiotics, which are produced by bacteria living on the ants, is a novel compound that could be used to treat fungal infections. The study, published in the journal Biomed Central (BMC) Biology, is the first to demonstrate that a single ant colony uses multiple antibiotics Attine ants cultivate the fungus Leucoagaricus gongylophorus, creating a rich growth medium out of chewed-up leaves and keeping it free of weeds. In return, the fungus serves as the ants' main food source. The well-studied attine ant Acromyrmex octospinosus, native to South and Central America, enjoys a mutually beneficial relationship with a variety of bacteria that produce antibiotics, which they use as weed killer. Fungiculture is a delicate art: contaminants - unwanted bacteria and fungi - can easily wipe out a fungus garden. A. octospinosus is a careful farmer. When setting up a new colony, the ants will seed a new fungus garden on a platform of rootlets set carefully apart from the underground nest, effectively keeping the garden protected from weeds. In addition, the ants clean their legs carefully before setting to work in the garden, further minimising the chance of contamination. In the current study, the researchers asked whether the ants have co-evolved with weed-killing bacteria, or whether they actually sample bacteria from the soil and select those species that make the most useful antibiotics. To find out, they isolated and studied bacteria from A. octospinosus worker ants. The team found that a species of Streptomyces which produces the well-known fungicide candicidin is most probably collected by the ants. But in the same colony they found that a species of Pseudonocardia, which produces a novel antifungal, most probably co-evolved with the ant. 'This was really a fun project which started with a PhD student, Joerg Barke, streaking leaf-cutting ants onto agar plates to isolate antibiotic producing bacteria,' said Dr Matthew Hutchings of the University of East Anglia in the UK. 'We found a new antifungal compound that is related to a clinically important antifungal named nystatin, so we're excited about the potential of these ants and other insects to provide us with new antibiotics for medical use.' The combination of co-evolved and collected bacteria provides the ants with a powerful collection of weed killers, allowing them to keep their food source safe from invaders. The findings are particularly important in light of the rising number of multi-drug-resistant infections in humans. The use of multiple antibiotics by the ants shows that these tiny creatures, which appeared on the scene between 8 and 12 million years ago, evolved both agriculture and natural antibiotic 'combination therapy' well before humans. 'Humans are just starting to realise that this is one way to slow down the rise of drug resistant bacteria - the so-called superbugs,' explained Dr Hutchings. The researchers are currently setting up an 'ant-cam' video feed of the ants at work.

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