The fungus Aspergillus niger is used for the industrial production of proteins and organic acids. Fungi like A. niger grow by producing thread-like structures which are surrounded by a cell wall. This cell wall is dynamic, carbohydrate-active enzymes produce, change and degrade the carbohydrates in the cell wall. The focus of this thesis is on the physiological roles and biochemical properties of the carbohydrate-active enzymes that are made during carbon starvation. In times of nutrient shortage, the fungus can reuse his previously stored energy and carbon – for example in the cell wall – to produce stress-resistant spores. It was investigated which genes encoding carbohydrate-active enzymes are activated during carbon starvation, and how they are regulated. Two of the identified enzymes are subsequently characterized biochemically; chitinase CfcA and α-1,3-glucanase AgnB. This chitinase was found to have a role in cell wall degradation during carbon starvation. In addition, a set of genes was found that code for carbohydrate-active enzymes that are specifically activated when the fungus produces spores. These were mainly enzymes that were predicted to be active on the cell wall carbohydrates chitin and β-1,3-glucan, such as the chitinases CfcI en CtcB. Biochemical characterization of chitinase CfcI showed that it has a for fungal chitinases new activity; CfcI breaks down short chitin chains by leaving of the sugar monomer. A clear understanding of the enzymatic mechanisms behind cell wall changes, provides a firm basis for enzyme engineering, and potentially allows improvement of industrial fermentations.
|Translated title of the contribution||Koolhydraat-actieve enzymen actief op de celwand van Aspergillus niger: Biochemische eigenschappen en fysiologische rollen gedurende autolyse en differentiatie|
|Qualification||Doctor of Philosophy|
|Publication status||Published - 2014|