Characteristics of glucose uptake by glucose- and NH4-limited grown Penicillium ochrochloron at low, medium and high glucose concentration

Abstract

Glucose uptake by Penicillium ochrochloron (formerly Penicillium simplicissimum) was studied from 0.01 to 400mM glucose using chemostat culture and bioreactor batch culture. The characteristics of glucose uptake varied considerably with the conditions of growth, harvest and uptake assay. Glucose-limited grown mycelium showed one saturable transport system [KS below 0.01mM; vmax 1.1–1.2mmol (gdry weight)−1h−1] plus a first order process (permeability P=1.2×10−7cms−1). Ammonium-limited grown mycelium showed only one saturable transport system [KS 0.3–0.7mM; vmax 0.5–0.8mmol (gdry weight)−1h−1]. During exponential growth at high glucose concentration (300–400mM) a first order process was found with a P value of 5.6−9.3×10−7cms−1. After ammonium exhaustion a second first order phase showed a lower P value (6.1–9.3×10−8cms−1). A similar change in permeability was also found after a re-evaluation of published data for Gibberella fujikuroi, Aspergillus niger, Aspergillus awamori and Saccharomycopsis lipolytica. For the first order processes simple diffusion was ruled out as a mechanism for glucose uptake. Glucose uptake by P. ochrochloron was controlled more strongly by metabolism than by transport and was not rate limiting for overflow metabolism.