2013 Annual Report
Extracellular hydrolase (enzyme that breaks down chemical bonds) activity is different in some strains of Aspergillus (A.) flavus used for biocontrol. This research is necessary to determine if introduced non-aflatoxigenic biocontrol A. flavus would be less or more likely to cause damage to the crop. The research was done by ARS scientists in the Food and Feed Safety Research Unit at Southern Regional Research Center, New Orleans, LA. Afla-guard, an atoxigenic strain used for biocontrol of aflatoxin in corn, produced lower pectinolytic activity (ability to break down pectin) when pectin (a complex sugar found in cell walls) was used for enzyme induction than either AF36, a strain used predominantly for biocontrol of aflatoxin in cottonseed, or the wild-type aflatoxin-producing A. flavus used for comparison. Generally, xylanolytic (ability to break down xylan, another complex sugar) and pectanolytic activities were similar for all strains when the fungi were grown on a natural substrate, corn. These studies show that there is no more likelihood for crop damage from the introduced biocontrol strain than from the natural populations in the agricultural fields.
Recombination among Aspergillus (A.) flavus isolates. Assessing the ability of A. flavus to outcross (introducing unrelated genetic material) is necessary to accurately determine the fate of introduced non-aflatoxigenic biocontrol strains to mediate aflatoxin production. Work was done by scientists at North Carolina State University, Department of Plant Pathology, Raleigh, NC and in the Food and Feed Safety Research Unit at the Southern Regional Research Center, New Orleans, LA. Out-crossing among A. flavus mutants and wild-type strains has been proven to occur under laboratory conditions and under conditions closely mimicking field conditions. Out-crossing can occur between strains from different vegetative compatibility groups (VCGs) proving that VCG is not a barrier to recombination. Mating type populations dictate both the isolate’s ability to out-cross as well as its ability to infect the seed. Formation of sexual structures allowing such out-crossing can occur under optimal conditions in as little as two months. This research provides strong evidence that outcrossing among biocontrol and natural populations in the field is likely to occur within a single growing season and refutes prior studies that suggested that such outcrossing could not occur.
Chettri, P., Ehrlich, K., Cary, J.W., Collemare, J., Cox, M.P., Griffiths, S.A., Olson, M.A., De Wit, P.J., Bradshaw, R.E. 2013. Dothistromin genes at multiple separate loci are regulated by AflR. Fungal Genetics and Biology. 51:12-20.
Ehrlich, K., Mack, B.M., Wei, Q., Li, P., Roze, L.V., Dazzo, F., Cary, J.W., Bhatnagar, D., Linz, J.E. 2012. Association with AflR in endosomes reveals new functions for AflJ in aflatoxin biosynthesis. Toxins. 4:1582-1600.
Bradshaw, R.E., Slot, J.C., Moore, G.G., Chettri, P., De Wit, P., Ehrlich, K., Ganley, A., Olson, M.A., Rokas, A., Carbone, I., Cox, M.P. 2013. Fragmentation of an aflatoxin-like gene cluster in a forest pathogen. New Phytologist. 198:525-535.
Chang, P., Ehrlich, K. 2013. Genome-wide analysis of the Zn(II)2Cys6 zinc cluster-encoding gene family in Aspergillus flavus. Applied Microbiology and Biotechnology. 97(10):4289-4300.
Chang, P-K., Scharfenstein, L.L., Mack, B.M., Ehrlich, K. 2012. Deletion of the Aspergillus flavus orthologue of A. nidulans fluG reduces conidiation and promotes production of sclerotia but does not abolish aflatoxin biosynthesis. Applied and Environmental Microbiology. 78(21):7557-7563.
Chang, P.-K., Scharfenstein, L.L., Ehrlich, K., Wei, Q., Bhatnagar, D., Ingber, B.F. 2012. Effects of laeA deletion on Aspergillus flavus conidial development and hydrophobicity may contribute to loss of aflatoxin production. Fungal Biology. 116:298-307.
Mellon, J.E., Zelaya, C.A., Dowd, M.K., Beltz, S.B., Klich, M.A. 2012. Inhibitory effects of gossypol, gossypolone, and apogossypolone on a collection of economically important filamentous fungi. Journal of Agricultural and Food Chemistry. 60:2740-2745.
Mellon, J.E., Dowd, M.K., Beltz, S.B. 2013. Effects of temperature and medium composition on inhibitory activities of gossypol-related compounds against aflatoxigenic fungi. Journal of Applied Microbiology. 115:179-186.