Regulation of ammonia assimilation in ammonia-limited chemostat cultures of Escherichia coli ML 30: Evidence of bistability

✍ Scribed by Dr. P. J. Müller; Beate von Frommannshausen; H. Schütz

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 778 KB
• Volume: 21
• Category: Article
• ISSN: 0233-111X
• DOI: 10.1002/jobm.19810210503

✦ Synopsis

I n a preceding paper evidence of two stationary stable states (bistability) in the specific activity of glutamine synthetase (GS) in ammonia-limited steady-state cultures of Escherichia coli ML 30 at dilution rates (D) about 0.15 h-l was described (MULLER et aE. 1977). For better understanding of the regulation mechanisms leading to GS bistability chemostat experiments were performed over a wide range of dilution rates up t o D = 0.8 h-l. For each steady state the specific activities of GS and glutamate dehydrogenase (GDH) -the other key enzyme of the two NH, assimilation routes in E. coliand in addition the remaining NH, concentration in the culture liquid were determined.

Parallel to GS bistability two states of GDH activity andNH, concentration are found. The higher state of GS is connected with a lower GDH activity and NH, concentration. With rising D the GS activities decrease whereas GDH activities and NH, concentrations increase.

Since no adenylation of the GS is detectable GS bistability seems to be regulated on the level of enzyme synthesis like GDH bistability.

From t h e experimental findings a mathematical model is derived based on the bottle neck enzyme theory of growth. It describes the dependence between the specific growth rates on the one hand and the specific enzyme activities and NH, concentration on the other. It is shown t h a t the specific uptake rate of the limiting NH, and the specific growth rates, respectively, depend on the simultaneous action of two bottle neck enzymes which are connected by a regulative link.

Chemostat cultures allow to investigate the enzyme regulation in microorganisms under steady-state conditions in dependence on the specific growth rate (p) or dilution