PRODUCTION OF L-ORNITHINE BY ARGININE AUXOTROPHIC MUTANTS OF BREVIBACTERIUM-KETOGLUTAMICUM IN DUAL SUBSTRATE-LIMITED CONTINUOUS-CULTURE

Production of L-ornithine under dual limitation of arginine and phosph ate was investigated in a chemostat culture of an arginine auxotroph o f Brevibacterium ketoglutamicum. Under an arginine-limited condition, culture instability, including the formation of revertant cells, could be a serious problem due to the inherent instability of the auxotroph ic mutant strain. The difference in the growth rates between the auxot rophs and revertants was considered to be the main cause of the cultur e instability, and dual Limitation with arginine and phosphate was fou nd most appropriate to overcome this problem. When the ratio of the ph osphate to arginine concentration in the feed medium was varied betwee n 0.55 and 5.22 at a fixed dilution rate of 0.1 h(-1), three distinct growth phases were recognized: phosphate-limited (0.55 to 2.01), dual arginine- and phosphate-limited (2.01 to 2.16) and arginine-limited (a bove 2.16). In the dual arginine- and phosphate- limitation phase, the culture stability was markedly improved while the yield of L-ornithin e was maintained at a high level. When the dilution rate was varied fr om 0.04 h(-1) to 0.17 h(-1) under the dual-limitation condition, maxim um L-ornithine productivity was obtained at a value of 0.27 g/l/h at D =0.1 h(-1).