It's a mould breaker. Researchers have discovered the first fungus that behaves like a farmer.
We already know that soil fungi can help bacteria travel quickly from A to B. The fungal filaments provide favourable conditions for the bacteria, and so act as "highways" through the soil. But these highways may impose a toll.
To find out more, Pilar Junier at the University of Neuchâtel, Switzerland, and her colleagues studied the soil fungus Morchella crassipes and its relationship with Pseudomonas putida bacteria. To track the flow of nutrients, she labelled the fungus with carbon-13 in one experimental set-up, and labelled the bacteria with the isotope in a second. After five days, the bacteria had gained nutrients from the fungus.
But between day five and day nine, the bacteria numbers began to drop and the nutrients flowed from bacteria into the fungus. At the same time, the fungus began growing hard, nutrient-rich nodules called sclerotia, which it uses as a food store during unfavourable times when nutrients are unavailable.
Feed 'em and reap
Junier thinks the fungus first cultivates the bacteria by feeding them, and then harvests them. The fungus may actually eat the bacteria, although it's not clear how. "We think digestive enzymes are involved," she says.
"The interaction between fungi and bacteria certainly deserves further study," says Duur Aanen at Wageningen University and Research Centre in The Netherlands. However, he is not convinced that the interaction qualifies as farming.
"It is unclear whether the documented carbon transfer from bacteria to fungus makes a nutritional difference for the fungus," says Ulrich Mueller at the University of Texas at Austin.
However, Debbie Brock at Washington University in St Louis, Missouri, is more receptive. In 2011 she documented the only other proposed example of farming outside the animal kingdom, in which the social amoeba Dictyostelium discoideum cultivates and harvests bacteria.
"Microbes are still a largely unexplored frontier," she says. "I am sure there are many, many amazing relationships among microbes waiting to be discovered and investigated."
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2013.2242
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