Production of xanthan by in-flow cultures of Xanthomonas campestris |
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Authors: | J. Carlos Roseiro A. Nick Emery P. Simões F. Estêvão M. T. Amaral-Collaço |
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Affiliation: | (1) Departamento de Technologia das Industrias Quimicas, Unidade de Microbiologia Industrial-Biotechnologia, Laboratório Nacional de Engenharia e Technologia Industrial, Azinhaga dos Lameiros, 1699 Lisbon Codex, Portugal;(2) Centre for Biochemical Engineering, School of Chemical Engineering, University of Birmingham, P.O. Box 363, B15 2TT Birmingham, UK |
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Abstract: | The kinetics of xanthan formation in Xanthomonas campestris continuous and fed-batch fermentations was studied along with metabolic changes due to growth rate variation. A maximum growth rate within the range 0.11–0.12 h–1 was obtained from the continuous culture data in defined medium, producing xanthan at rates up to 0.36 g l–1 h–1 corresponding to a maximum 67% glucose conversion at a dilution rate (D) of 0.05 h–1. Comparatively, fed-batch cultivation was more efficient, producing maximum xanthan at 0.75 g l–1 h–1 and 63% glucose conversion at 0.1 h–1. When reaching D=0.062 h–1 in continuous cultures, a change was observed and the values of the specific rate of substrate consumption shifted, initiating an uncoupled growth region expressing a lack of balance of the catabolic and anabolic reactions. The deviation was not accompanied by a change in specific xanthan production indicating that xanthan metabolism was not affected by D. For fed-batch-grown X. campestris cells within the range D=0.03–0.1 h–1, both metabolic parameters changed linearly with the growth rate showing a wide region coupled to growth. Outside that range, glucose accumulated and the specific xanthan production dropped, suggesting substrate inhibition.Correspondence to: J. C. Roseiro |
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