Sugar Uptake and Kinetics in Aspergillus niger

Aspergillus niger predominantly grows on dead decaying plant material which mostly consists of polysaccharides like hemicellulose and pectin. These structural heteropolysacharides represent a significant part of agriculture waste that is currently insufficiently used.

Having the capacity to degrade plant cell wall wastes, this filamentous ascomycete can hydrolyse sugar polymers due to high levels of excreted enzymes, and further ferment both hexose as well as pentose monomer substrates.

Besides glucose, sugar monomers in hemicellulose can include xylose (in higher amounts), mannose, rhamnose, arabinose, and small amounts of galacturonic acid. Pectins on the other hand are rich in galacturonic acid. The mentioned substrates were selected for kinetic and uptake studies.

Preliminary experiments consisted of batch cultivations on both single carbon sources and an equimolar mixture of these. All carbon sources have been characterized in terms of biomass yields and maximum growth rates. Interestingly, in combination, some of the carbon sources were consumed simultaneously and some sequentially.

Previously, a well-defined chemostat protocol and tools for quantitative metabolomics were developed and optimized for A. niger (Lameiras, Heijnen, & van Gulik, 2015). With these tools, an accelerostat experiment was performed on a mixture of six sugars for characterization of the transport kinetics. It was found that the uptake of glucose, xylose and mannose could be described with Michaelis Menten kinetics, while the uptake of arabinose, galacturonic acid and rhamnose appeared to be inhibited by the presence of other sugars.

References:

Lameiras, F., Heijnen, J. J., & van Gulik, W. M. (2015). Development of tools for quantitative intracellular metabolomics of Aspergillus niger chemostat cultures. Metabolomics, 11(5), 1253–1264. doi:10.1007/s11306-015-0781-z