Enhanced bioproduction of chitin in engineered Pichia pastoris

Biopolymer chitin and its derivatives have a wide range of applications in different fields. Chitin is primarily produced from marine crustacean by strong acid and strong alkali treatment. To reduce the environmental hazardous in the production of chitin, post-fermentation fungal biomass waste like fungi cell walls provides a viable alternative source for chitin. In this study, improved chitin content in yeast cell wall was achieved by overexpressing chitin biosyntheic pathway related genes. The chitin content was 51.5 μg/mg cell wall and 122.9 μg/mg cell wall in strain GS-1.10 (gfat, uap and chs1 genes overexpression) and strain GS-2.6 (gfat, gna1, agm1, uap and chs1 genes overexpression), which were 44.3% and 244.4% higher than that in control strain GS115, respectively. By overexpressing another chitin synthase gene (chs3), the chitin content in strain GS-3.10 was further increased to 136.2 μg/mg cell wall, which was 10.8% and 281.6% higher than that in GS-2.6 and in control GS115, respectively. Moreover, chitin yield was further improved by various culture conditions optimization, and reached 162.4 μg/mg cell wall, which was 4.43 times of that in the starting strain GS115. The final titer of chitin was 2.23 g/L culture broth in 84 h fed-batch fermentation in a 5 L bioreactor. To our knowledge, this is the first report of chitin production in engineered Pichia pastoris via biosynthetic pathway enhancement.