Specific oxygen uptake rate as indicator of cell response of Rhodococcus erythropolis cultures to shear effects

Specific oxygen uptake rate, qO2, on Rhodococcus erythropolis IGTS8 cultures has been measured under different fluid dynamic conditions in a STBR, changing stirrer speed, between 100 and 700 rpm, and air flow rate, between 1 and 10 L min−1. Experimental results indicate that qO2 values for R. erythropolis cultures can be influenced by the fluid dynamics inside the bioreactor. Under non oxygen-limited conditions, the oxygen consumption rate by the cells does not depend on the oxygen transfer rate; hence, the specific oxygen uptake rate is constant. However, when the stirrer speed is increased over a limit value, around 450 rpm in the culture studied, a change is clearly detected and, as higher stirrer speeds are used, specific oxygen uptake rate suffers a significant decrease. Nevertheless, when the hydrodynamics are varied changing the air flow rate, between 1 and 10 L min−1, this variable does not affect the oxygen uptake rate. According to these results, specific oxygen uptake rate measurement provides a good indication of whole stress generated by the hydrodynamic conditions into the bioreactor. A simple method to determine changes into the cell response due to the fluid dynamic environment in the bioreactor is herein proposed. According to this method, shear effects on the culture can be detected by the change on specific oxygen uptake rate measured at laboratory scale, employing the usual gas in-gas out dynamic method. This assay combines oxygen transfer, oxygen uptake rate and possible cell damage in a one simple method that can considerably simplify and accelerate fundamental research on the development and scale-up of bioprocesses.