Production of a microbial lipase by Staphylococcus carnosus (pLipMut2) in a bubble column reactor and a centrifugal field bioreactor

Extracellular lipase production by the recombinant strain Staphylococcus carnosus (pLipMut2) has been studied. First substrate optimization was carried out in shaken cultures. As a result, the best substrate yield of 20 units/g (peptone + yeast extract) and maximum lipase activity in the culture supernatant of 1.7 units/cm³ could be obtained by a nutrient rich complex medium consisting of 75 kg/m³ yeast extract, 15 kg/m³ tryptone, 5 kg/m³ glucose and 0.5 kg/m³ K₂HPO₄. Higher initial substrate concentration caused inhibition of growth. Antifoam agent at higher levels than 1 cm³/ dm³ resulted in a negative influence on lipase yield. Comparative fermentation studies have been carried out in a bubble column reactor and in a centrifugal field bioreactor. Direct proportionality between growth, lipase production and oxygen consumption was observed. In the bubble column reactor usual superficial air velocities (4 cm/s) caused intensive foam generation, thus fermentation was only possible after installation of a broader column head to allow coalescence. In the centrifugal field bioreactor higher productivities were obtained without foam problems at superficial gas velocities which were one order of magnitude lower than in the bubble column. Fermentations have been performed batchwise and without holding pH constant. Neither pH control nor glucose feeding could improve the substrate yield further. Compared to former fermentation studies with the strain S. carnosus (pLipPS1) lipase yield (lipase activity/cell density) could be improved by 300% and substrate yield (lipase activity/substrate concentration) by 600%.