FUMONISIN PRODUCTION BY FUSARIUM SPECIES ON SOLID SUBSTRATES

Fumonisins were produced by strains of Fusarium moniliforme and F: pro liferatum on a medium consisting of 500 g yellow corn kernels and 500 mL distilled water added to a 30.5 x 61 cm autoclavable polyethylene b ag. The corn was inoculated by drawing a suspension from a lyophilized culture into a sterile 5 mL syringe fitted with a 19 gauge needle and injecting 1 mL through the side of each polyethylene culture bag. Bag s of inoculated corn were incubated in the dark at 20 degrees to 22 de grees C for 4 weeks. Seven to 8 days after inoculation, holes were pun ched near the tops of the bags to promote aeration. After a 4 week inc ubation, cultures were soaked in chloroform-acetone (50 + 50, v/v) in 4 L flasks overnight to kill fungus and to remove water. Next, the cul ture media was filtered through 2 mm nylon mesh screens and air dried from 24 to 48 h. Fumonisin concentrations were determined by liquid ch romatography/o-phthalaldialdehyde fluorescence. Confirmation was by ga s chromatography/mass spectrometry. We observed that the 3 most import ant factors in the production of fumonisins in bulk corn cultures were temperature control, moisture, and aeration. Extraction by acetonitri le-water (50 + 50, v/v) for 30 min produced the highest yields of fumo nisins. Measurable concentrations were reduced by as much as 50% when culture material was heated at 50 degrees C overnight. Fusarium monili forme strains consistently produced fumonisin B-1 as the major compone nt, but some strains of F. proliferatum produced fumonisin B-2 and/or fumonisin B-3 at higher concentrations than fumonisin B-1. Results wer e calculated on the basis of dried culture material.