Effects of fluid-dynamic conditions in Shimwellia blattae (p424IbPSO) cultures in stirred tank bioreactors: Hydrodynamic stress and change of metabolic routes by oxygen availability

Cultures of Shimwellia blattae (p424IbPSO) under different fluid dynamic conditions have been studied. Runs have been performed in a STBR changing the stirrer speed from 100 to 1200 rpm. Growth rates have been determined measuring biomass concentration with time. A kinetic model has been fitted to experimental data. Results show that hydrodynamic stress appears in experiments performed at high agitation, from 1000 to 1200 rpm. Moreover, cell viability has been measured by colony forming units, the hydrodynamic stress is evident from 800 rpm and a growth time of 15 h. In addition, metabolites produced during growth have been measured. The results point out that the oxygen availability has a big influence because the metabolite distribution clearly changes in runs carried out in conditions under which hydrodynamic stress does not appear yet but oxygen transfer rate has been increased. The increasing of stirrer speed provokes an increase in the oxygen transport and uptake rates, and in some cases, in the dissolved oxygen concentration, changing the metabolic routes favored and accordingly the product distribution. Moreover, cells cultured under different fluid dynamic and oxygen availability conditions present a different behavior when employed in resting cell showing, in general, a similar behavior to that detected in experiments employing growing cells.