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Glucose uptake and growth of glucose-limited chemostat cultures of Aspergillus niger and a disruptant lacking MstA, a high-affinity glucose transporter

Bjarne R. Poulsen^2,

George J. G. Ruijter^2,

Jaap Visser^2,

¹ Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
² Section Molecular Genetics of Industrial Microorganisms, Wageningen University, Dreijenlaan 2, 6703 HA Wageningen, The Netherlands
³ Leiden University, Institute of Biology Leiden, Clusius Laboratory, Department of Fungal Genetics and Metabolomics, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands

Correspondence
Jens J. L. Iversen
jjli{at}bmb.sdu.dk

This is a study of high-affinity glucose uptake in Aspergillus niger and the effect of disruption of a high-affinity monosaccharide-transporter gene, mstA. The substrate saturation constant (K_s) of a reference strain was about 15 µM in glucose-limited chemostat culture. Disruption of mstA resulted in a two- to fivefold reduction in affinity for glucose and led to expression of a low-affinity glucose transport gene, mstC, at high dilution rate. The effect of mstA disruption was more subtle at low and intermediate dilution rates, pointing to some degree of functional redundancy in the high-affinity uptake system of A. niger. The mstA disruptant and a reference strain were cultivated in glucose-limited chemostat cultures at low, intermediate and high dilution rate (D=0.07 h^–1, 0.14 h^–1 and 0.20 h^–1). Mycelium harvested from steady-state cultures was subjected to glucose uptake assays, and analysed for expression of mstA and two other transporter genes, mstC and mstF. The capacity for glucose uptake (v_max) of both strains was significantly reduced at low dilution rate. The glucose uptake assays revealed complex uptake kinetics. This impeded accurate determination of maximum specific uptake rates (v_max) and apparent affinity constants () at intermediate and high dilution rate. Two high-affinity glucose transporter genes, mstA and mstF, were expressed at all three dilution rates in chemostat cultures, in contrast to batch culture, where only mstC was expressed. Expression patterns of the three transporter genes suggested differential regulation and functionality of their products.

Present address: Department of Clinical Genetics, Erasmus Medical Center, PO Box 1738, 3000 DR Rotterdam, The Netherlands.

Present address: Fungal Genetics and Technology Consultancy, PO Box 396, 6700 AJ Wageningen, The Netherlands.

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