Relation between pellet fragmentation kinetics and cellulolytic enzymes production by Aspergillus niger in conventional bioreactor with different impellers.

The hydrodynamic environment in bioreactors affects the oxygen transfer rate and the shear conditions during microbial cultivations. Therefore, assessment of the effect of the hydrodynamic environment on cellular morphology can contribute to favoring the production of metabolites of interest. The aim of this work was to use image analysis in order to quantify the fragmentation of Aspergillus niger pellets in a conventional bioreactor operated using different impeller speeds, air flow rates, and impeller configurations including Rushton turbines and Elephant Ear impellers, with evaluation of the influence of the hydrodynamic environment on the production of cellulolytic enzymes. An empirical kinetic model was proposed to describe the dynamics of pellet fragmentation and quantify the shear conditions. The results showed that the agitation speed affected the dynamics of pellet fragmentation in two ways, by accelerating the damage process and by increasing the magnitude of the fragmentation. Both endoglucanase and β-glucosidase production exhibited a linear relationship with the pellet fragmentation percentage, which was directly related to the shear conditions. Interestingly, β-glucosidase production was favored under high shear conditions, while the highest endoglucanase production occurred under low shear conditions. These findings may be useful for defining suitable systems and operating conditions for the production of metabolites including enzymes in bioreactors, as well as defining conditions that favour a specific pre-determined enzyme cocktail.