Use of autoradiography to quantify aspects of fungal growth and starvation in submerged liquid culture

Abstract

Autoradiographic analyses, using N -acetyl-[ 3 H]-D-glucosamine, were made of steady state chemostat, shear-stressed and nutrient-starved populations of Trichoderma aureoviride . The proportion of actively growing hyphal tips was dilution rate dependent and varied from approximately 45 % at low rates (0.02 h −1 ) to 75 % at rates approaching the maximum specific growth rate. These data have been used to calculate a true specific growth rate, μ h , of the fungus at different steady state dilution rates. The proportion of growing tips was also affected by the impeller stirring rate and varied in a complex way as a function of mixing efficiency, shear damage to the hyphae and, probably, the ability of the fungus to synthesize shear resistant walls at high liquid shear rates. Shear stress produced only small changes in the macromolecular composition of the mycelium and neither the adenylate energy charge nor the efficiency of RNA in protein synthesis were adversely affected even at the highest shear rates imposed. Carbon starvation of glucose-limited populations resulted in immediate and rapid hyphal wall turnover as judged by N -acetyl-glucosamine incorporation and a cessation of polar growth. Starvation also induced sporulation and the process was almost complete after 30 h of starvation.