Optimization of in vitro growth conditions of Pyrenophora teres for production of the phytotoxin aspergillomarasmine A

摘要

In liquid cultures of Pyrenophora teres, three phytotoxins may be found: L,L-N-(2-amino-2-carboxyethyl) aspartic acid (toxin A), anhydtoasperigillomarasmine A (toxin B) and asperigillomarasmine A (toxin C). In particular, toxins A and C cause chlorotic and necrotic symptoms in detached barley leaves, toxin C being the damaging, whereas toxin B is only weakly phytotoxic. When P. teres is grown in liquid modified Fries medium, toxim B is the main toxin accumulated, possibly due to a ring closure of toxin C at the low pH value of th emedium. The amount of toxin B produced by 11 isolates of P. teres was compared in modified Fries medium. Generally, the most virulent isolates of P. teres produced higher amounts of toxin B than the less virulent isolates. During growth, the pH of the media decreased from 6.7 to about 3.0-3.5, followed by a slight increase to about 3.5-4.0. All isolates, except one, produced toxin B, whereas only two isolates produced toxin C and toxin A. Maintaining th epH at about 6.5 by sterile tritation with 1 M MaOH resulted in a shift in toxin accumulation from toxin B to toxin C. The addition of tris or phosphate buffer to the media resulted in higher pH during the growth period, an increase in the total amounto of toxins produced, and a shift in toxin accumulation from toxin B to toxin C. The higher pH value probably prevented the conversion of toxin C to toxin B. No toxins were produced in two routinely used media, potatoe glucose broth and grass broth. Toxin B and toxin C were purified by ion exchange chromatography and precipitation with HCl.