Effectiveness of the toxin-degrading strain screening strategy: Deficiency and improvement in screening the gossypol-degrading microorganism Aspergillus niger

Abstract Background The gossypol, as an antinutritional factor or natural plant toxin, has antifertility effects on humans and animals, exists in cottonseed oil and meal, and is a typical food or feed contaminant. It is the classic screening method to using acetate gossypol as the sole carbon sources to prepare selective medium and screening gossypol-degrading microorganisms. By the classic screening strategy, many researchers have discovered that some microorganisms, and Aspergillus niger is the most reported microorganism. A strain of A. niger which can grow in an agar solid medium with gossypol as the sole carbon source is isolated from cattle rumen liquid was obtained by classic screening strategy. The effectiveness of the classic screening strategy was verified, by duplicating and verifying the degradation of gossypol by the A. niger. Results the A. niger can reduce the free gossypol (FG) content through biosorption but has no effect on the total gossypol (TG) content. And it can secrete agarase, utilise agar as carbon source. Conclusions The A. niger can secrete agarase, but cannot effectively degrade gossypol, In this case, it will mislead researchers and lead them to make wrong judgments. The usual methods of previous screening strategies are not rigorous enough, the classic screening method has defect in screening toxin-degrading strain, so agar control group should be added.