EFFECTS OF OILSEED STORAGE PROTEINS ON AFLATOXIN PRODUCTION BY ASPERGILLUS-FLAVUS

Potential involvement of seed storage proteins in susceptibility to af latoxin contamination was assessed with in vitro tests. Initially, two oilseed storage proteins [cottonseed storage protein (CSP) and zein] were compared with bovine serum albumin (BSA) and collagen. Supplement ation of a complete defined medium with either oilseed storage protein resulted in significantly more aflatoxin production by Aspergillus fl avus than supplementation with either BSA or collagen. Little or no af latoxin was produced when either BSA, CSP, or zein was employed (at 0. 5%) as both the sole carbon and the sole nitrogen source. Media with c ollagen (0.5%) as the sole nitrogen and carbon source supported aflato xin production similar to the complete defined medium. Although lower than levels observed with defined medium, aflatoxin production increas ed with both increasing CSP concentration (0 to 2.0%) and increasing z ein concentration (CI to 6.0%) when these proteins served as both the sole carbon and sole nitrogen source. Denaturing polyacrylamide gel el ectrophoresis and protease activity assays indicated that fungal acqui sition of protein carbon was probably via hydrolysis mediated by the 3 5 kD metalloprotease of A. flavus. Media lacking nitrogen but containi ng sucrose (5.0%) and supplemented with either zein (1.7%) or CSP (2.0 %) supported three- to eightfold more aflatoxin production than the co mplete defined medium. The results suggest seed storage proteins, when present with an accessible carbon source, may predispose oilseed crop s to support production of high levels of aflatoxins by A. flavus duri ng seed infection.