Biological Warfare - Soil: Reflections on the Basis of our Existence - page 108

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The double life of fungi . One group of soil fungi are the fungal world's equivalent of carnivorous
plants, deploying ingenious mechanisms to capture nematodes. The nematode in the photo has
just swum into two retractable snares. Once captured, the fungus grows its hyphae into the nema-
tode and breaks down its nitrogen-rich body
The image sequence shows how the snare functions. When the fungi have registered the nem-
atode's presence, the cells swell up and trap the unsuspecting victim

or rings that trap nematodes. Once the nematode has fastened in the vice-like grip,
the fungus penetrates it and fills it with digestive hyphae.
Wondering if I could enlist the help of nematophagous fungi to save myself the
task of removing all my greenhouse soil, I contacted Professor Birgit Nordbring
Hertz, who has spent much of her professional life studying these fungi. She
explained that she had always been aware of the fungi's potential as biological
agents but had chosen to focus her studies on their fascinating double life. As well
as building ingenious traps for nematodes, nematophagous fungi also exist like other
fungi by decomposing organic matter in the soil. Discovering why and how the fungi
alternate between these two approaches has been Professor Hertz's holy grail.
The answer to this question would help me to answer my own query: is it
worth investing in nematophagous fungi or is it simply better to bite the bullet and
change the greenhouse soil?
It is thought that the fungi trap nematodes as nitrogen substitutes when there
is a deficit of nitrogen in the soil, in the same way as sundews trap insects in and
around nitrogen-poor bogs. All the chicken manure and compost in the soil means
there is no shortage of nitrogen in my greenhouse, so I doubt the fungi would help.
But nematode traps do have effective uses. Ruminants like sheep and cattle are
prone to nematode infestation and the roundworm, also a nematode, can infect
humans. When a cow becomes infected, the nematode's eggs end up in the ani-
mal's manure, from where new nematodes hatch and lie in the grass waiting to be
eaten during grazing. Once inside the cow, they develop into adulthood and lay
new eggs, continuing the cycle until the cattle become ill from nematode infesta-
tion in their gut. If farmers feed nematophagous fungi to their cattle, the spores
pass through the animals and end up in the manure. There they germinate and start
capturing nematodes, interrupting the microorganisms' reproductive onslaught and
allowing the cattle to recover. Unlike their soil-dwelling congeners, these fungi are
effective at producing traps in nutrient-rich substrates like cowpats, perhaps due to
the density of nematodes in this substrate.
Nematode traps have yet to catch on commercially, but proponents suggest it
is just a question of ironing out a few technical issues before commercialisation
can begin. The pharmaceutical companies that produce livestock drugs are less
enthusiastic and would rather develop a chemical product that is easier to admin-
ister (treatments containing live fungi must be kept in certain conditions to pre-
serve their effectiveness). However, the chemical agents used to kill nematodes are
problematic, over time causing resistance in cattle and dwindling in effectiveness.
Large herds are especially vulnerable to nematodes, especially if they graze for