Model-based estimation of optimal dissolved oxygen profile in Agrobacterium sp. fed-batch fermentation for improvement of curdlan production under nitrogen-limited condition

Dissolved oxygen tension (DOT) is an important factor influencing curdlan fermentative production by Agrobacterium sp. ATCC 31749. Therefore, optimization of dissolved oxygen profile is crucial to improve curdlan production. In this study, an unstructured mathematical models that consider nitrogen source as growth-limiting substrates were developed to estimate the kinetic parameters of cell growth, curdlan formation, and glucose consumption during Agrobacterium sp. ATCC 31749 fermentation at various DOTs (5-75%). The estimated kinetic parameters were used to establish models with Origin 8.0. All models of kinetic parameters were coupled with the kinetic model derived from Agrobacterium sp. ATCC 31749 fermentation to determine the effect of DOT on curdlan fermentation. The combined kinetic models satisfactorily fit the experimental data. The optimal dissolved oxygen profile was obtained using genetic algorithms coupled with iterative dynamic programming algorithms in MATLAB 10b. The optimal dissolved oxygen during curdlan production (20-120 h) was approximately 52% DOT, and the maximum curdlan concentration of 48.5 g/L was obtained at this DOT profile. To our knowledge, this study is the first to optimize DOT for curdlan fermentation under nitrogen-limited conditions. This report significantly contributes to the improvement of curdlan production on an industrial scale.