Tiny creatures make a massive impact

Worms have a reputation for disease and destruction but they also play a crucial role in food production, says Dr Roy Neilson

The pitch at Murrayfield Stadium in Edinburgh is treated with a garlic spray. Picture: Ian Rutherford

THE changing climate and the need to produce more food to feed a growing global population is putting pressure on our natural resources. Soil is one of our most precious natural commodities and it is recognised that soils need protection. One way to achieve this is to preserve the ecology of our soil by monitoring its health and quality, and by developing integrated approaches to pest management.

An excellent biological early-warning system of environmental change is naturally provided by a biological family that gardeners, pet owners and farmers are well acquainted with: the humble worm, or nematode.

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Nematodes are everywhere, and most of us will have knowingly or otherwise come into contact with them during our lives – even avid rugby fans who recently watched Murrayfield being churned up as a result of a nematode infestation of the pitch.

A handful of healthy soil will contain at least 10,000 nematodes. They are diverse, with approximately 26,000 species known to science – and this is considered a tiny fraction of the total number.

Arguably, nematodes are the most abundant multicellular animal on the planet, but being microscopic in size, they remain unseen to most of us. Yet their diminutive size is in stark contrast to the impact that pathogenic nematode species can have on their animal, human or plant hosts.

In developing countries, nematodes are responsible for some of the most horrendous human diseases, eg elephantiasis. Conservative estimates by the World Health Organisation suggest that more than 130 million people worldwide have nematode-related diseases. Globally, more than £60 billion per annum is spent combatting the effects of nematodes in agriculture through, for example, the application of nematicides – which, in an environmental context, is unsustainable.

There is considerable research at the James Hutton Institute to breed new crop varieties resistant to nematode feeding and to identify environmentally friendly methods of nematode control. In developed countries the impact on agriculture is primarily economic, measured in reduced yield. One of the most humbling experiences of my research career was visiting a rural African village where nematodes had devastated the crops to such an extent that there was not sufficient food produced for that year.

In common with recent tree disease outbreaks, globalisation coupled with a changing climate increases opportunities for the introduction and establishment of new pathogenic nematode species. Our regulatory authorities are thus constantly monitoring imports of food and wood products to intercept these threats.

Historically, pathogenic species have given nematodes a bad press. However, as nematology (the study of nematodes) progresses, so does our understanding of the potential benefits that nematodes can provide. In 1998, the first animal genome to be completely sequenced was that of a bacterial feeding nematode, Caenorhabditis elegans. Since then it has become a model organism in biomedical research, particularly for novel drug targets, as this nematode species and humans were found to share many disease-associated genes. Consequently such research has been instrumental in medical breakthroughs in diseases including Alzheimer’s, Type 2 Diabetes, Parkinson’s and depression.

Recently, nematode ecology research has expanded. We now know that for every one pathogenic nematode in soil, there are approximately ten beneficial nematodes. These good guys are involved in the turnover of organic matter and the provision of nutrients that are ultimately taken up by plants. In terms of sustainable food production, the maintenance of these beneficial nematodes is crucial. We can now classify nematodes into five major feeding groups: those that feed on bacteria, fungi and plants, as well as scavengers and predators.

Many of us will be familiar with human DNA fingerprinting through television shows such as CSI. Using the same general principles at the James Hutton Institute, we have developed a DNA-based tool that fingerprints the entire soil nematode community based on the major nematode feeding groups. We are creating a baseline fingerprint for each soil sample, and by monitoring through time we can use changes in these nematode communities to assess and understand the effects of environmental change. Not only does this provide us with an important tool to help maintain an environmental balance for sustainable food production but it can help maintain fragile Scottish habitats such as the Machair.

So the next time you worm your pet or step outside, remember the role of the humble nematode in the ecology of our soils, and therefore in the ongoing quest for food security.

• Dr Roy Neilson is rhizosphere ecologist at the James Hutton Institute. www.hutton.ac.uk