Carbon Dioxide Fixation and Conidiation in Fusarium culmorum Grown in Continuous Culture

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Abstract
The rate of CO2 fixation by F. culmorum during vegetative growth in glucose-limited continuous culture at pH 3.5 was 0.036 .mu.mol CO2 fixed (mg hyphae)-1 h-1; during conidium production at pH 6.5 it reached a maximum value of 0.29 .mu.mol CO2 fixed (mg hyphae)-1 h-1. During growth in phosphate-limited continuous cultures, containing sufficient glucose to suppress conidiation, the rate of CO2 fixation was 0.045 .mu.mol CO2 fixed (mg hyphae)-1 h-1 and did not increase substantially following an increase in pH to 6.5. The internal hyphal pH remained at approximately 6.5 despite changes in the eternal pH from 3.5-6.5. Phosphoenolpyruvate carboxykinase (EC 4.1.1.32) and pyruvate carboxylase (EC 6.4.1.1) activities estimated in hyphal extracts gave a fixation rate approximately 3 times the rate of CO2 fixation in vivo in glucose-limited and phosphate-limited vegetative continuous cultures at pH 3.5. In conidiating cultures, phosphoenolpyruvate carboxykinase and pyruvate carboxylase activities approximately equalled the highest CO2 fixation rates in vivo. Fixed 14C was distributed among all the major cell components, with the highest percentage in the conidial protein fraction.