A fermentation system designed to independently evaluate mixing and/or oxygen tension effects in microbial processes: development, application and performance
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In order to evaluate the independent effects of hydrodynamic conditions and/or oxygen tension on culture physiology and productivity, a fermentation system designed to control dissolved oxygen at constant power drawn (P/V) was developed. The system included a fully instrumented 14 l bioreactor coupled to a PC for data acquisition and control. Power drawn was measured (using a commercial torquemeter coupled to the shaft) and maintained constant by varying the agitation speed; while gas blending was used to control dissolved oxygen concentration. To validate the system, rheological-complex fermentations involving xanthan gum production and filamentous fungal cultivation (using Xanthomonas campestris and Trichoderma harzianum) were developed. In both cases, and despite the changing environmental conditions (due to increased broth viscosities and microbial respiration), both variables were controlled at the desired set points. Through such a system, a rigorous evaluation of the hydrodynamic conditions and/or oxygen tension on culture physiology and productivity is now feasible.
KeywordsDissolved oxygen tension (DOT) Fermentation system Power drawn Rheological-complex cultures Trichoderma harzianum Xanthomonas campestris
The financial support of CONACyT (39906 and U44098), IFS (E/2548-2) and DGAPA-UNAM (226202) is gratefully acknowledged. JARV thanks CONACyT for his postdoctoral fellowship. We thank C. Flores and M. Ortiz for strain maintenance. The technical support of A. Aguilar, R. Godoy and D. Llorente in the construction of the fermentation system is acknowledged with thanks. The authors also thank J.M. Hurtado and S. Ainsworth for computer support and bibliographic assistance.
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