Dynamic responses of Pseudomonas fluorescens DF57 to nitrogen or carbon source addition

Cultures of Pseudomonas fluorescens DF57 were grown on different carbon and nitrogen sources. Glucose, succinate and acetate were used as carbon sourc e and pulsed to an aerobic steady-state cultivation of P. fluorescens DF57 at D = 0.1 h(-1) with citrate as limiting carbon source. Glucose was utilis ed with the fastest uptake rate (19.4 C mmol l(-1) h(-1))compared to succin ate (8.8 C mmol l(-1) h(-1)) and acetate (4.3 C mmol l(-1) h(-1)). Acetate triggered an inhibition of cellular metabolism, which resulted in 2-h long growth arrest after its addition to the steady-state culture. The influence of the nitrogen source was investigated in an aerobic cultivation on a mix ture of ammonium and nitrate as limiting nitrogen sources and citrate as no n-limiting carbon source. When ammonia and nitrate were pulsed to the stead y-state culture, they were mainly assimilated into biomass with a maximum u ptake rate of 111 and 33 mg N l(-1) h(-1), respectively. Nitrate uptake was never complete as the residual concentration in the chemostat cultivation was 30 mg N l(-1) nitrate. A pulse of nitrite in the cultivation broth resu lted in an inhibition of the growth but not of the primary metabolism, as n itrite was taken up at 38 mg N l(-1) h(-1), citrate was consumed and cofact ors were produced continuously. In all experiments, oxygen was used as elec tron acceptor. (C) 2001 Elsevier Science B.V. All rights reserved.