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 51.5μg/mg cell wall and 122.9μg/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 136.2μg/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 162.4μg/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.