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Smarty ants: agriculture, antibiotic use and biofuels?

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Ants tending their fungal garden

Ants are amazing insects, and fungus-growing ants are perhaps the most amazing of all. This group includes the leafcutter ants that you’ve probably seen on David Attenborough’s TV programmes, carrying carefully cut leaf fragments to their nests along well-defined trails in the rainforest. Millions of ants can be found within a single underground nest the size of a three-storey house. Brilliantly, and without using a single moving part, the nests are perfectly air conditioned – maintaining constant temperature and humidity.

“But wait,” I hear you cry. “This is all very well, but what does it have to do with microbiology?” Well, did you ever wonder what the ants do with the leaves that they so diligently carry through the jungle? They don’t eat them; instead, they strip the waxy coating from the surface of the leaf and feed the mashed-up leaf material to a symbiotic fungus that they grow in ‘gardens’ found within the colony.

This fungus is the sole food source for their colonies and has co-evolved with the ants over 50 million years, during which it has developed structures rich in sugars and fats that the ants harvest to feed to their larvae and queen.

The ants also live in symbiosis with another organism: antibiotic-producing bacteria known as actinomycetes. These bugs, which cover the ants as a visible white dust, provide the ants with antibiotics in return for food. The ants use these antibiotics to prevent opportunistic pathogenic fungi from growing in the nest. If they were allowed to grow, these invaders would destroy the garden, starving the ants and leading to the collapse of the whole colony.

Despite each ant having a brain smaller than a grass seed, these ant colonies provide the perfect environment to selectively grow a single species of fungus and form a complex symbiosis with bacteria that enables them to protect themselves and their food. Leafcutter ants developed both agriculture and antibiotic use tens of millions of years before humans existed. Think about that for a bit.

If that weren’t enough, a new paper has discovered that this amazing ant–microbe symbiosis is even more complex then previously thought. Researchers have shown that it’s not just the farmed fungus that breaks down the leaf material: a whole community of bacterial species live alongside the fungi, secreting enzymes that help the fungus do its job. A fungus that grows well is great for the ants because they have more food to eat, but it might be useful for humans, too, by representing an efficient way to convert plant mass into sugars and then into biofuels such as ethanol and butanol.

Matt Hutchings

As an added bonus, here’s a link to our Leafcutter Ant Cam!

Aylward FO, Burnum KE, Scott JJ, Suen G, Tringe SG, Adams SM, Barry KW, Nicora CD, Piehowski PD, Purvine SO, Starrett GJ, Goodwin LA, Smith RD, Lipton MS, & Currie CR (2012). Metagenomic and metaproteomic insights into bacterial communities in leaf-cutter ant fungus gardens. The ISME journal PMID: 22378535

Image credit: Anna Jordan, John Innes Centre Entomology Department
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Written by microbelog

22/03/2012 at 5:37 pm

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