Abstract
In its natural environment, the filamentous fungus Aspergillus niger grows on decaying fruits and plant material, thereby enzymatically degrading the lignocellulosic constituents (lignin, cellulose, hemicellulose, and pectin) into a mixture of mono- and oligosaccharides. To investigate the kinetics and stoichiometry of growth of this fungus on lignocellulosic sugars, we carried out batch cultivations on six representative monosaccharides (glucose, xylose, mannose, rhamnose, arabinose, and galacturonic acid) and a mixture of these. Growth on these substrates was characterized in terms of biomass yields, oxygen/biomass ratios, and specific conversion rates. Interestingly, in combination, some of the carbon sources were consumed simultaneously and some sequentially. With a previously developed protocol, a sequential chemostat cultivation experiment was performed on a feed mixture of the six substrates. We found that the uptake of glucose, xylose, and mannose could be described with a Michaelis–Menten-type kinetics; however, these carbon sources seem to be competing for the same transport systems, while the uptake of arabinose, galacturonic acid, and rhamnose appeared to be repressed by the presence of other substrates.
Highlights
In white biotechnology, the feedstock represents the highest cost factor in the production of bulk chemicals
We studied the capacity of A. niger for uptake of six-selected monosaccharides present in lignocellulosic biomass, that is, three C6 sugars two C5 sugars, and a sugar acid
As a preliminary experiment to investigate which carbon sources would sustain growth and whether growth on different carbon sources would lead to different morphologies, A. niger was cultivated on minimal medium in shake flasks with six different substrates
Summary
The feedstock represents the highest cost factor in the production of bulk chemicals. There is an increasing interest in using cheaper biomass streams as feedstock for industrial biotechnology processes, the so-called second-generation feedstocks. The second-generation feedstocks have the advantage that they do not compete with food supplies, but have the disadvantage that they are much more complex than firstgeneration ones. The second-generation feedstocks consist of mixtures of different fermentable carbon sources from plant biomass of agricultural crops waste, which are currently insufficiently used. Of the global 200 × 109 tons per year of plant biomass produced, over 90% is lignocellulose. About 8–20 × 109 tons of this biomass is potentially accessible, but remains unexploited [1]
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