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Researchers To Combat Toxic Brown Mould With Its Non-toxic Cousin

August 12, 2005
University of Bonn
Scientists from the University of Bonn and the IITA in Nigeria, want to combat the highly toxic mould Aspergillus flavus by an unusual method: they 'inoculate' the fields with a variant of aspergillus which cannot produce any toxin in the hope that the 'good' mould will displace the 'bad'. They are being supported in this by US researchers from Arizona, who by using this method have been able to reduce the aflatoxin contamination of cotton by 98 per cent.

Blood withdrawal with a child in Bénin. With 99 of 100 children from Benin and Togo Aflatoxin in the blood can be proven.
Credit: Image courtesy of University of Bonn

In the early 1960s more than 100,000 turkeysdied in Britain of cancer of the liver. Eventually, researchersidentified mouldy peanut flour from Brazil containing large amounts ofaflatoxin as the cause of this mysterious 'turkey X' disease. Eventoday the toxin is regarded as one of the most virulent naturalcarcinogenic substances.

The tasteless toxin is produced by the mould aspergillusflavus. It grows in hot, arid regions, in the south-west of the US andin many regions of Africa and Asia. In Third World countries,particularly, this dangerous paintbrush-shaped mould is ubiquitous.This may be one reason for the high rate of liver cancer in Africa."Our colleagues from the IITA in Nigeria recently succeeded in provingthat 99 out of 100 children from Benin and Togo had aflatoxin in theirblood," Professor Richard Sikora of the Bonn Institute of PlantDiseases explains. "The consequence is drastic impairment of growth andof other types of development."

'Good' mould displaces its highly toxic cousin

The remedy may lie in the idea of US researchers Dr. Peter J.Cotty, which is both simple and ingenious. "In addition to thedangerous strain aspergillus flavus there are also others which cannotproduce any toxin," the Bonn plant pathologist Dr. Sebastian Kiewnickexplains. "Cotty propagated this non-toxic strain of aspergillus ongrains of corn and spread the mould-infected grains in fields ofcotton. As a result, the non-toxic strain was present in substantiallylarger amounts and was thus able to almost entirely supplant the toxicvariety." The success was overwhelming: aflatoxin infection of thecotton cobs dropped from an average of 1,000 ppb (parts per billion) tobelow 20 ppb, thereby lying within the US safety limit for animal food -- cotton seeds serve as food e.g. for dairy cattle.

Two years ago the 'good' mould was permitted in the US as anorganic pesticide. Five kilos of mould-infected grains of corn aresufficient to 'inoculate' an area of one hectare -- this means that themethod is relatively inexpensive. "For developing countries,particularly, this would be the ideal strategy to get the upper hand ofthe aflatoxin problem," Professor Sikora thinks.

He has had quite a lot of experience with combating tropicalplant diseases. For two years the Bonn team, together with colleaguesfrom the IITA in Benin and Nigeria, have been looking for a mouldisolate which is guaranteed to be unable to produce aflatoxin -- afterall, they do not want to fight Satan with Beelzebub. "Apart from thatthe aspergillus variant has to be so sturdy that it can assert itselfagainst its toxic cousin in the wild," Professor Sikora says.

Promising strains among 3,000 isolates

The Federal Ministry of Economic Co-operation and Development(the BMZ) is supporting the project until 2006 to the tune of a totalof 1.2 million euros. The researchers have made an important advance:"We have examined 3,000 isolates in all and have come across severalpromising strains," Sebastian Kiewnick states. "Now we'll soon beconducting the first field trials." Should they be successful, the teamwant to develop a quick and easy method for propagating the non-toxicmould for use en masse.

There is no danger of additional damage as a result of'inoculating' the fields with mould, it is claimed. "It can scarcely beprevented that maize or nuts will be infected to a certain extent withbrown mould," Sebastian Kiewnick emphasises. "We can only influencewhich strain of aspergillus grows on it: a dangerous producer of toxins -- or the non-toxic variant."

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University of Bonn. "Researchers To Combat Toxic Brown Mould With Its Non-toxic Cousin." ScienceDaily. ScienceDaily, 12 August 2005. <>.
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