Study On The Fermentation And Metabolic Characteristics Of Microbial Polysaccharide-Curdlan In CSTR

Curdlan is an extra-cellular polysaccharide produced by Alcaligenes faecalis or Agrobacterium species. It has extensive applications in food industry for its peculiar thermo-gelling property. In this work, the kinetics of A. faecalis and characteristics of cell growth and curdlan production were investigated. Metabolic network of A. faecalis was preliminarily constructed and main nodal points in metabolic network were analyzed and determined.It was showed that the kinetics of cell growth and glucose consumption wereμ=0.227S/(0.177+S) and qS=4.338μ+0.021, respectively, under glucose-limited conditions. At the same times, under NH₄Cl-limited conditions, kinetic of cell growth wasμ=0.619S/(0.162+S), and kinetics of glucose consumption and curdlan production were q_S=3.906μ+0.384 and q_P=251 mg/(g-cell·h), respectively. The growth maintenance coefficient under NH4Cl-limited conditions was two times than that of under glucose-limited conditions.The characteristics of cell growth and curdlan production were investigated and the results showed that the productivity of cell growth in continuous cultivation was 98% higher than that of batch fermentation at least. However, the productivity of curdlan production was decreased comparing that of batch fermentation. The specific production rate of curdlan was improved by 39% and 73%. The productivity of cell growth was proportional to glucose/NH₄Cl consumption ratio under glucose-limited culture condition. Meanwhile, the productivity of cell growth and curdlan productivity was related to the glucose/NH4Cl consumption ratio.A metabolic flux mass balance model of Alcaligenes faecalis was preliminarily constructed and the distribution of metabolic flux was determined. The results showed that G-6-P was an important flexible nodal point and PYR was a weak rigidity nodal point. Metabolic flux of HMP, HMP and ED pathways were decreased in the curdlan production phase. The HMP pathway flux was decreased significantly by 13%. With the increased dilution rate, the mass flux of curdlan synthesis pathway was transferred to HMP pathway, where more energy produced to support the exo-polysaccharide biosynthesis.