A fermentation system designed to independently evaluate mixing and/or oxygen tension effects in microbial processes: development, application and performance

Abstract

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.

Morphogenesis of Streptomyces in Submerged Cultures

“…Most studies show an optimum stirring speed for production of the metabolite of interest, where initially the production increases with stirrer speed and then decreases again at very high speeds (Heydarian et al, 1999;Large, Ison, & Williams, 1998;Mehmood et al, 2010;Roubos, Krabben, de Laat, Babuška, & Heijnen, 2002). Because oxygen transfer is closely linked with agitation, the effects of the one from the other need to be distinguished (Bartholomew, Karow, Sfat, & Wilhelm, 1950a, 1950bMehmood et al, 2010;Rocha-Valadez, Albiter, Caro, Serrano-Carreón, & Galindo, 2007;Shioya, Morikawa, Kajihara, & Shimizu, 1999). Leakage of lipase into culture fluid, indicative of cell damage, was exclusively observed in stirred vessels (Ohta et al, 1995).…”

Effects of carbon/nitrogen ratio, dissolved oxygen and impeller type on gellan gum production in Sphingomonas paucimobilis

“…The inhomogeneity caused by poor mixing in reactors containing high viscosity fluids makes the fermentation process difficult to control (Rocha Valadez et al 2007), with the resulting nutrient and oxygen transfer limitations being the critical factors found to restrict gellan gum production (Dreveton et al 1996). The available information concerning the effects of DO and mixing conditions on gellan gum production is limited and still controversial.…”

Oxygen transfer and bubble sizes occurring in a pilot‐scale cultivation of Bacillus velezensis 83 for the production of poly(γ‐glutamic acid) under two schemes of power drawn

“…There are several methods to measure this parameter in stirred tank reactors, as detailed by Ascanio et al 18 For pilot-plant stirred reactors, the most reliable method measures the shaft torque using a torquemeter. 19 Commercial bench and pilot-scale fermenters are rarely equipped with torquemeters. This is an important limitation as the power input (and not the stirring speed) is a crucial parameter determining the yields and productivity of fermentation processes.…”