Biocompetition as a tool to cope with the problem of aflatoxin contamination of food and feed commodities: may phenotype microarray technology contribute to the individuation of "good" competitors?

Aspergillus flavus is a well known plant pathogen responsible of economic losses and food safety concern due to the ability of mycotoxin production. Aflatoxin contamination of crops is a significant problem worldwide, and many Countries have set more or less strict limits for mycotoxin presence in feed and food commodities. An interesting strategy to cope with aflatoxin contamination in susceptible crops involves the use of intraspecific competition to interfere with mycotoxin production by the relevant Aspergillus flavus strains. Atoxigenic A. flavus strains (afla-), unable to produce the relevant mycotoxin, have been already used as bio-competitors to decrease aflatoxin accumulation on cotton, maize and peanuts fields. Selecting a strain performing as a strong bio-competitor is not a straightforward task since it depends on previous assessment of various interacting factors conditioning the relative fitness of the strains in a given ecological niche. Reconstruction experiment have been generally performed in laboratory conditions to uncover the biological mechanisms underlying the efficacy of atoxigenic strains in preventing aflatoxin production and/or to give a preliminary indication of strain performance when released in the field. Our present goal is 1) characterization of A. flavus population colonizing the corn field of the Po valley and 2) setting a strategy for the identification of “good” competitors among afla- strains isolated from the above mentioned A. flavus population. For this purpose we are performing competition experiments in laboratory conditions and designing “high throughput” procedures to test as many as possible environmental conditions that may affect competition efficacy. Moreover, afla- strains are generally considered to be derived from aflatoxin producer strains (afla+) that have lost the capacity to produce the relevant mycotoxin as a result of mutation(s) affecting gene(s) belonging to the Aflatoxin biosynthetic cluster. afla- strains are obviously expected to be altered in one or more steps of secondary metabolism. However the story might be more complex than expected, since regulatory interactions between pathways of primary and secondary metabolism have already been described. In this respect, Phenotype MicroArray technology may represent an additional value for our goal if the specific metabolic features of different afla- strains could be correlated to their competitive ability. In the present study we have performed, as a preliminary approach, experiments to verify if afla+ and afla- strains may be differentiated by the use of the Biolog FF physiological identification kit.