Improved curdlan fermentation process based on optimization of dissolved oxygen combined with pH control and metabolic characterization of Agrobacterium sp. ATCC 31749
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A significant problem in scale-down cultures, rarely studied for metabolic characterization and curdlan-producing Agrobacterium sp. ATCC 31749, is the presence of dissolved oxygen (DO) gradients combined with pH control. Constant DO, between 5% and 75%, was maintained during batch fermentations by manipulating the agitation with PID system. Fermentation, metabolic and kinetic characterization studies were conducted in a scale-down system. The curdlan yield, intracellular nucleotide levels and glucose conversion efficiency into curdlan were significantly affected by DO concentrations. The optimum DO concentrations for curdlan production were 45–60%. The average curdlan yield, curdlan productivity and glucose conversion efficiency into curdlan were enhanced by 80%, 66% and 32%, respectively, compared to that at 15% DO. No apparent difference in the gel strength of the resulting curdlan was detected. The comparison of curdlan biosynthesis and cellular nucleotide levels showed that curdlan production had positive relationship with intracellular levels of UTP, ADP, AMP, NAD+, NADH and UDP-glucose. The curdlan productivity under 45% DO and 60% DO was different during 20–50 h. However, after 60 h curdlan productivity of both conditions was similar. On that basis, a simple and reproducible two-stage DO control process for curdlan production was developed. Curdlan production yield reached 42.8 g/l, an increase of 30% compared to that of the single agitation speed control process.
KeywordsAgrobacterium sp. ATCC 31749 Curdlan Dissolved oxygen Two-stage DO control strategy Kinetic characterization
This work was supported by research grants from the National Natural Science Foundation of China (20676055, 60604028 and 20806034), Ministry of Science and Technology of China (National Basic Research Program of China, 2007CB714303) and Research on the Preparation Technology of Edible Emulsifier and its Industrialization (National Key-technologies R&D Program of China, 2011BAD23B00). The work was also supported by the Program for Introducing Talents of Discipline to the Universities, No. 111-2-06. The authors would like to thank these organizations for their kind financial support.
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