Wednesday, 30 October 2013

A Fungus That Farms Bacteria!

Morrell (Morchella crassipes)
First fungal farmers found harvesting bacteria - life - 30 October 2013 - New Scientist

People who study biology, and particularly ecology, are of course used to finding examples of how 'selfish' genes very often create cooperative associations. In fact all ecosystems are in reality composed of far more cooperative organism than they are of competitive ones. But nature can still throw up a few surprises and so give us that little frisson of excitement and wonder or a gasp of astonishment.

We like to think that it takes something akin to human intelligence to come up with something like farming where another species is looked after, protected and nurtured in order to provide us with food so it still surprises people to discover that we are not the only ones doing it. Leaf-cutter ants, for example, collect leaves which are chewed up to form a compost on which a unique fungus grows in special chambers in the underground nest. The ants in turn live on the fungus, which they harvest, having planted the spores on their garden. The forty-seven species of leaf-cutter ant have been doing it for so long that they each have their own species of Lepiotaceae fungus which has co-evolved with them.

Microbes are still a largely unexplored frontier. I am sure there are many, many amazing relationships among microbes waiting to be discovered and investigated.

Debbie Brock, Washington University in St Louis, Missouri, USA
Another common example of cooperation is that between the legume family of plants - the pea and bean family, which includes acacia trees, lupins, peanuts and laburnum trees - and bacteria which live in special nodules in the roots. These bacteria 'fix' free atmospheric nitrogen by turning it into nitrates which are then available to the plant. As such they are an important and integral part of Earth's nitrogen cycle which is essential to all life on the planet.

Also essential for a healthy planet, and particularly for healthy trees and forests, is a cooperative alliance between several species of fungi and trees, and many other plants. One of the mysteries of botany when I was a biology student many years ago was how tall trees manage to overcome gravity to push water from the roots to the leaves at the top of the tree and with it the nutrients the trees need especially in the growing tips of the branches.

Tall tree-trunks are of course a product of an evolutionary arms race but, as we now know, they would have been impossible had it not been for a sybiotic relationship between fungi in the soil and tree roots. The fungi get sugars from the tree and in return provide the tree with nutrients which they make available and which they help actively transport into the root system with enough pressure to push the sap up the tree's vascular system, helped by capillary action and suction pressure from evaporation through pores in leaves.

Now scientists have discovered a fungus which farms bacteria.

Pilar Junier of the University of Neuchâtel, Switzerland, and colleagues have discovered that the fungus Morchella crassipes has formed a relationship with the bacteria Pseudomonas putida. By labelling the fungi with radioactive carbon-13 in one set-up and the bacteria in a second, they were able to show that the bacteria multiplied quickly in the first five days as they took nutrients from the fungus. However, numbers fell quickly between day five and day nine and nutrients were taken up by the fungus, which grew hard nodules which acted as a nutrient store.

The fungi actively fed and protected the bacteria, then ate them, probably producing digestive enzymes with which to do so. In principle, and biologically, no different to what we do with cereal crops, cabbages, carrots, chickens, sheep and cows and a host of other species with which our human genes have formed an alliance.

According to Oprah Winfrey, if you're an atheist, you're not supposed to find that fact awesome and amazing; you have to suffer from an infantile superstition and attribute it to magic for that.

Reference:
Bacterial farming by the fungus Morchella crassipes, Martin Pion, Jorge E. Spangenberg, Anaele Simon, Saskia Bindschedler, Coralie Flury, Auriel Chatelain, Redouan Bshary, Daniel Job and Pilar Junier;
Proc. R. Soc. B 22 December 2013 vol. 280 no. 1773.

First fungal farmers found harvesting bacteria, Colin Barras, New Scientist 30 October 2013

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