Inhibition of aflatoxin production by myxobacteria : Nannocystis exedens, Stigmatella erecta

Inhibition of fungal growth and aflatoxin production by two members of the myxobacteria as a bio control agent was studied. Aspergillus flavus ATCC 26946 and Aspergillus parasiticus NRRL 3145 were grown in the presence of Nannocystis exedens ATCC 25963 and Stigmatella erecta ATCC 25191 in 50 ml modified potato dextrose broth and incubated at 28°C. After 7 and 14 days incubation time, mycelial mat was extracted, dried and weighed to determine fungal growth while the aflatoxins in the broth were extracted using chloroform by separation and quantitation using high pressure liquid chromatography. The addition of Nannocystis exedens to Aspergillus parasiticus and Aspergillus flavus significantly reduced mycelial growth at 7 days incubution time (p<0.05). Mycelial growth was significantly reduced (p<0.05) when Nannocystis exedens was added to the broth containing the aflatoxigenic mold held at 14 days, while significant mycelial reduction were recorded at 14 days when Stigmatella erecta was added . Production of aflatoxin G₁ was significantly reduced (p<0.05) at 7 days incubation time in the presence of Nannocystis exedens while aflatoxins B₁ and G₁ were significantly reduced (p<0.05) at 14 days, when similar treatments were applied. Results show that approximately log 3 CFU/ml of Nannocystis exedens population is required to reduce Aspergillus parasiticus and Aspergillus flavus population of log 1 CFU/ml to non detectable levels on solid media. There was no significant reduction of mycelial growth (p>0.05) when Nannocystis exedens was placed in a dialysis membranes of 8000 Daltons and 300000 Daltons suggesting that the inhibitory action may be due to a parasitic action rather than the excretion of an enzyme or antibiotics.