1996 WINNER

How fungi are mushrooming

Fungi are incredible networkers, says Tom Wakeford

By Tom Wakeford

BENEATH your lawn there is an energy network more powerful than the National Grid, yet made of filaments far smaller than fibre-optic threads. While the human world wires itself up to the Internet, fungi are being recognised as the original networkers of nature.

A conceptual breakthrough has allowed microbiologists on both sides of the Atlantic to make a series of remarkable discoveries about the mushroom and its relatives. "Looking underground," says researcher Alan Rayner, "we are uncovering a new vocabulary of evolution."

With their mania for mergers and potential immortality, fungi pose a challenge to the notion of biological individuality.

Think of a whale in the ocean. We see its huge bulk only when it comes up for air. Most of the time, it swims hidden from view, scouring the seas for food.

Now think of a toadstool under a tree in your local wood. Its real body is underneath the soil's surface, a huge cotton-wool mass of branching tubes that can spread for tens of yards. in every direction. This mound of mould can be as large as a whale but is usually invisible to our above-ground eye.

Every mushroom and toadstool is a signal that a fungus has come up for air. It needs the air, not to breathe like a whale, but rather to take its offspring to new sources of food. Masquerading as an independent entity, a mushroom is merely a spore-dispersing device for the sleeping giant below.

Myron Smith at Toronto University has discovered one mammoth fungus that spreads its tentacles under 15 hectares of virgin forest in Montana, weighs 100 tons, and is more than 1,000 years old. Such monstrosities may be more the rule than the exception, he suggests. At around half a ton, fairy-rings are a little more weighty than their name and appearance suggest.

Computer models of fungal growth have turned out to be far more challenging to construct than are similar models of insect or bird populations. Unlike butterflies or sparrows, fungi are so interconnected that it is often hard to know when one ends and another begins.

And unlike a human or a modern motor car, both "born to die" within a fairly predictable time span, fungi have the potential immortality of a electricity or telephone network that is continuously updated. Akin to the Internet, the mass of intercommunicating fungal tubes also has no single centre of command. Now, a team of biologists at Bath University, led by Dr Rayner, has devised a method of modelling a growing fungus that draws on the properties of moving fluids. Like drops on a window pane, fungal growth tubes are continually dividing and merging. The patterns foraging fungi produce are forged partly by their genes, and partly by the environment that they encounter.

A good analogy is a meandering countryside river. "The form of a river is defined by its banks," says Dr Rayner, "but the position of these banks is produced not just by the flow of the river, but by the landscape through which it flows. You cannot separate the two." The same balance between internal and external factors exists in his biological model of fungal growth.

PRESENTED with an obstacle, fungi can draw on this self-plumbing and, like flood-water at a dam, surge through at the blockage's weakest point. When branching, the fungal filaments show two distinct patterns. One is dense like a conifer branch, the other more sparse like an oak.

Dr Rayner believes that the different patterns reflect what resources surround the foraging fungus. The conifer pattern explores food-patches more exhaustively, whereas the sparse branching allows faster progress across a barren area.

Even their sex is a fluid concept. While most organisms must find the right time and place, underground fungal filaments can mate using any part of their body at almost any time. Not confined to just two sexes, fungal species can couple with thousands of possible "mating types".

Fungi are the biological kingdom's alliance-makers. The fungal condition allows them to thrive - not because they necessarily excel at any single survival skill, but because they can draw on a diverse network of expertise.

All this might make one wonder, as we switch on the kettle, pick up the phone, or log-on to the Internet, whether humans really are the first species to have a worldwide web.

Tom Wakeford, 25, is finishing his doctorate on molecular ecology at the Department of Biology, University of York. He is using molecular biology to study rhizobia, bacteria that appear in the root nodules of plants that are able to fix nitrogen from the atmosphere. In particular, he wants to find out whether bacteria near the root are genetically the same as or different from those in the soil