Effects of mixing on fed-batch fermentation of L-ornithine

The effects of mixing on L-ornithine fermentation were studied using an c-a rginine auxotrophic mutant of Brevibacterium ketoglutamicum ATCC 21092. Thr ee different modes of fed-batch culture using two different impeller types were studied in a 7l fermentor. The first two modes of fed-batch culture we re carried out in a fermenter equipped with six-hat-blade disk-turbine impe llers with top and bottom feeding. The third mode of fed batch culture was carried out using pitched-six-flat-blade disk-turbine impellers with top fe eding. The titre of L-ornithine increased up to 1.8 fold with bottom-feedin g or when the pitched-six-flat-blade disk-turbine impellers were used compa red to when the six-hat-blade disk-turbine impellers with top-feeding were used. It was observed that the mixing time of the limiting nutrients varied significantly depending on both the direction of feeding and the impeller type. Since the profiles of the specific rates of CO2 evolution, oxygen and glucose uptakes were very similar for the three culture modes, it could be reasonably assumed that the microorganism exhibited similar growth rates f or each mode used. However, different amino acid producing activities were observed in the three culture modes. From these results it is concluded tha t the productivity of L-ornithine fermentation is significantly improved by shortening the mixing time of the limiting nutrient in the fermenter.