The influence of hydrodynamic conditions in a laboratory-scale bioreactor on pseudomonas aeruginosa metabolite production

Highlights
This study demonstrated that the process production of Pseudomonas aeruginosa metabolites might be successfully carried out by using a batch bioreactor. This process is dependent on the hydrodynamic conditions. Therefore, we tested and analyzed the fluid behaviour for gassed and ungassed conditions with the application of the various types of hydrodynamic criteria (e.g., power consumption, mixing time, mixing energy, the volumetric gas-liquid mass transfer coefficient). The obtained hydrodynamic parameters might be successfully used in the bioprocessing of the different substances with the application of the tested bioreactor. The growth and metabolite production of Pseudomonas aeruginosa was analyzed under selected hydrodynamic conditions. We found that the highest oxygen mass transfer is connected with the most intensive pyocyanin production. The rhamnolipids were produced under low mixing conditions and moderate oxygen mass transfer. The obtained data showed that the process production of Pseudomonas aeruginosa metabolites is possible with the use of a batch bioreactor. It should be emphasized that the hydrodynamic conditions in the used mixing system have strongly influenced the obtained product. Therefore, the hydrodynamic analysis for bioprocessing or process production of bioproducts with the application of the mixing systems is required.

Abstract
Hydrodynamic conditions are critical in bioprocessing because they influence oxygen availability for cultured cells. Processes in typical laboratory bioreactors need optimization of these conditions using mixing and aeration control to obtain high production of the desired bioproduct. It could be done by experiments supported by computational fluid dynamics (CFD) modeling. In this work, we characterized parameters such as mixing time, power consumption and mass transfer in a 2 L bioreactor. Based on the obtained results, we chose a set of nine process parameters to test the hydrodynamic impact on a selected bioprocess (mixing in the range of 0–160 rpm and aeration in the range of 0–250 ccm). Therefore, we conducted experiments with P. aeruginosa culture and assessed how various hydrodynamic conditions influenced biomass, pyocyanin and rhamnolipid production. We found that a relatively high mass transfer of oxygen (kLa = 0.0013 s−1) connected with intensive mixing (160 rpm) leads to the highest output of pyocyanin production. In contrast, rhamnolipid production reached maximal efficiency under moderate oxygen mass transfer (kLa = 0.0005 s−1) and less intense mixing (in the range of 0–60 rpm). The results indicate that manipulating hydrodynamics inside the bioreactor allows control of the process and may lead to a change in the metabolites produced by bacterial cells.