Aspergillus flavus can contaminate corn, groundnuts and other oil seed crops with acutely toxic and carcinogenic aflatoxin. Atoxigenic biocontrol strains of A. flavus reduce aflatoxin of toxigenic strains in a thigmoregulated manner. G protein-coupled receptor (GPCR) mutants of A. flavus were obtained from Nancy Keller at the University of Wisconsin. Since GPCRs are membrane bound proteins involved in signaling, we determined whether loss of signal receptor proteins affected intraspecific aflatoxin inhibition. Aflatoxin production was quantified using HPLC of extracts from four-day old, glucose-salts medium cultures grown in 24-well plates. Several atoxigenic isolates, both commercially developed biocontrol strains and isolates from Louisiana, were screened against the wild-type CA14 and the CA14N1 Nit mutant (the genetic background for gene knock outs) for intraspecific aflatoxin inhibition. Only two strains from Louisiana completely inhibited aflatoxin production of CA14 and CA14N1. One inhibitory biocontrol strain was grown with the GPCR mutants to look for loss of biocontrol function. The biocontrol strain inhibited aflatoxin production in all mutants. Toxigenic strains can also have biocontrol ability and inhibit aflatoxin production, therefore the mutants were grown with four toxigenic strains representing small or large sclerotial strains of both mating types. Only two GPCR mutants did not inhibit aflatoxin production of the toxigenic strains. When non-inhibitory GPCR mutants were germinated 12 hours prior to inoculation (due to slow growth) with competing toxigenic strains, the ability to inhibit toxin production was restored. Giving the slow-growing GPCR mutants a head start presumably reduced aflatoxin production because competing germinated hyphae now touched within the 1st 12 hours. This reiterates earlier observations that touch must occur early during the germination of the toxigenic isolate, otherwise aflatoxin production will be unaltered by a competing strain. Single G protein-coupled receptor protein knockouts did not change aflatoxin inhibition, but further studies are needed during the 12-18 hour critical window to understand what signaling leads to successful intraspecific aflatoxin inhibition.
Full conference title:
The Fourteenth International Aspergillus Meeting, Asilomar Conference Center, Pacific Grove, CA, USA
- Asperfest 14 (2017)