Public defence, Biotechnology, MSc An Nguyen

Title of the thesis: Enhancing yeast chitin production: From targeted engineering to adaptive evolution 

Thesis defender: An Nguyen
Opponent: Prof. Verena Siewers, Chalmers University of Technology, Sweden
Custos: Prof. Paula Jouhten, Aalto University School of Chemical Engineering

Chitin is among the most abundant biopolymers in nature, forming the structural material of crustacean shells and fungal cell walls. It has established value in biomedicine, food preservation, agriculture and sustainable materials, yet almost all chitin used today is extracted from crustacean shells. This source, however, comes with drawbacks: inconsistent seasonal supply, chemically demanding extraction, and the presence of shellfish allergens.

Fungal biomass offers an appealing animal-free alternative, with a simpler extraction process and without the seasonal and geographical constraints of crustacean harvesting. Among fungi, baker's yeast (Saccharomyces cerevisiae) stands out: it is already cultivated at industrial scale, is well understood genetically, and is recognized as safe. The obstacle is quantity — chitin makes up only 1–2% of the cell wall of baker's yeast.

This thesis set out to overcome this bottleneck via two strategies. In the first, genetic switches were designed to activate the yeast's natural cell-wall integrity pathway, increasing chitin content roughly five-fold and enabling its co-production alongside other valuable compounds at bioreactor scale. In the second, adaptive laboratory evolution was used: yeast populations were cultured in the presence of an antifungal compound that weakens the yeast's cell wall, driving the cells to adapt over successive generations by over-producing chitin. Whole-genome sequencing of the chitin-rich population identified the enriched mutations, and a strain reconstructed with three of these mutations achieved a 7.2-fold increase in chitin content relative to the wild type. Further analysis indicated that this elevated content arises not from an increase in the abundance of the chitin-synthesizing machinery but more likely from changes in how that machinery is distributed within the cell. The thesis examined also how engineered traits persist over prolonged cultivation of cells, an essential consideration for any future industrial use.

Together, this work delivered a set of genetic and evolutionary tools for boosting chitin content in yeast. Furthermore, the demonstrated co-production possibility and the insights into the evolutionary persistence of traits help move yeast-derived chitin closer to industrial exploitation.

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.

Contact information: 
Email: an.a.nguyen@aalto.fi 
Phone: +3584578773529
Research Group: https://www.aalto.fi/en/school-of-chemical-engineering/microbial-physiology 
LinkedIn: linkedin.com/in/an-nguyen-17b196196