ARS | Publication request: Increased Sensitivity of Aspergillus flavus and Aspergillus parasiticus Aflatoxin Biosynthesis Polyketide Synthase Mutants to UVB Light

Submitted to: World Mycotoxin Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 28, 2010
Publication Date: September 7, 2010
Citation: Ehrlich, K., Wei, Q., Bhatnagar, D. 2010. Increased Sensitivity of Aspergillus flavus and Aspergillus parasiticus Aflatoxin Biosynthesis Polyketide Synthase Mutants to UVB Light. World Mycotoxin Journal. 3(3):263-270.

Interpretive Summary: Contamination of cottonseed with aflatoxin is a problem for cotton growers in Texas and Arizona because high levels of this mold toxin prevent its use as an animal feed. Aflatoxin is produced by a mold called Aspergillus flavus. Attempts to prevent contamination have relied on introducing a competitor Aspergillus that is incapable of making the toxin. However, the stability of this competitor strain in the soil and on the plant is unknown. Stability is important for long-term effectiveness of the treatment. We tested spore sensitivity of different mutants and wild-type to UVB light, a component of sunlight. Spores exposed to UVB light showed a 5 times lower ability to form colonies than the natural strain or strains that do not make aflatoxin but still are capable of producing pigments related to aflatoxin production. Our results suggest that spores of the most commonly used non-aflatoxigenic competitor strain may survive less well than the natural strains that are capable of making aflatoxins when exposed to sunlight.

Technical Abstract: One strategy to reduce aflatoxin contamination of corn and cottonseed is to introduce spores of atoxigenic strains as competitors. Using isogenic mutants we show that, upon 5 or 20 min exposure to 302 nm (UVB) light, the viability of conidia of A. parasiticus and A. flavus mutants lacking the ability to accumulate any aflatoxin precursor metabolite is reduced by five-fold compared to that of aflatoxin-producing strains or pigmented mutants that accumulate aflatoxin precursors. This result suggests that the long-term viability of introduced atoxigenic competitor strains may be lower than that of natural aflatoxin-producing isolates when exposed to sunlight.