Oxygen-uptake and oxygen mass-transfer rates in cultures of Pseudomonas putida [a genetically modified organism (GMO) able to desulfurize dibenzothiophene and its derivatives] have been determined in a stirred tank bioreactor under different transport conditions. The oxygen-uptake rate has been measured by applying a modified dynamic method using a step of pure oxygen, because of the very low oxygen concentration in the broth. A kinetic model is proposed, obtaining the kinetic parameter values: specific maintenance and yield coefficients. Volumetric mass-transfer coefficient, k L a, has been determined, in a wide interval of hydrodynamic conditions, and predicted using a theoretical model. An increase of the transport rate is detected with the increase of the biomass and oxygen-uptake rate, which is described by a biological enhancement factor, E, which is also calculated by a theoretical model. Experimental values of k L a and E are compared with those predicted by the models with good agreement. Influences of mass-transfer conditions have been observed in growth and desulfurization capability of the cells. The oxygen-dissolved concentration is calculated from the estimations of the oxygen-transfer rate and from the oxygen-uptake rate; the models proposed are able to reasonably predict the experimental change of the oxygen concentration with the time course of the process.
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Gómez et al. (2006) studied this question.