Relation between pristinamycins production by Streptomyces pristinaespiralis, power dissipation and volumetric gas–liquid mass transfer coefficient, kLa

During bioreactor cultures, microorganisms are submitted to non-optimal conditions such as nutritional and hydrodynamic stresses which may lead to modifications of the physiological cell response; this is especially true for filamentous microorganisms like Streptomycetes also subjected to significant morphological changes. In the present work, growth and production of pristinamycins by Streptomyces pristinaespiralis in shaking flasks have been related to power dissipation. The filamentous bacteria were grown in different flask conditions with various total and working volumes and at two agitation rates, to test the influence of power dissipation and gas–liquid mass transfer coefficient on growth and antibiotics production. As a first step, computational fluid dynamics–volume of fluid (CFD–VOF) calculations were shown to be able to predict power dissipations for the various operating conditions in Newtonian flow conditions. Then, in non-Newtonian flow conditions (biomass concentration superior to 14 g L−1), the rheological model of Sisko was implemented in CFD simulations for the calculation of the fluid viscosity and then of power dissipation. Whereas microbial growth was correlated to kLa, the antibiotics production onset was linked to the volume mean power dissipation. Once a minimal cell concentration of 15 g L−1 was reached, the concentration of antibiotics was correlated to power dissipation with an optimal range of production, between 5.5 and 8.5 kW m−3. Higher power dissipation entailed a drop in production which could be explained by hydrodynamic cell damages.