Heterokaryosis between Aspergillus oryzae cyclopiazonic acid-defective strains: method for estimating the risk of inducing toxin production among cyclopiazonic acid-defective industrial strains.

Aspergillus oryzae strains are used extensively in the food industry. Some of these strains excrete alpha-cyclopiazonic acid (CPA), a mycotoxin which may provoke toxicoses in rats. Physicochemical methods may reveal the presence of this toxin, but they are inadequate to screen CPA-nonproducing (CPA-) strains. CPA production is revealed by either bacterial growth inhibition or alkalinization of the culture medium. This first biological property was used to devise a time-saving screening method to isolate mutants affected in their ability to produce CPA. The second method was used as a further test. After N-methyl-N'-nitro-N-nitrosoguanidine treatment, we isolated CPA- mutants from CPA producer strains (CPA+) and CPA+ mutants from CPA- strains. The mutants unable to produce CPA may be used in the food industry to reduce or eliminate the risk of intoxication in humans. Heterokaryon formation between different mutant strains was carried out to evaluate the risks of obtaining CPA from a mixture of mutants modified in their ability to synthesize this toxin. Pairings between two CPA+ strains always gave rise to CPA+ heterokaryons. Pairings between CPA+ and CPA- strains led, most often, to CPA+ heterokaryons. This could be directly correlated to the more frequent genotype (CPA+) in the heterokaryon. CPA hypoproducer and hyperproducer heterokaryons were obtained. Pairings between CPA- strains always gave rise to CPA- heterokaryons. These results suggest that the risks of producing this toxin from two CPA- individuals are not high.