Nitrite and ammonia assimilation by anaerobic continuous cultures of Escherichia coli

Cole, J. A., Coleman, K. J., Compton, B. E., Kavanagh, B. M. and Keevil, C. W. (1974) Nitrite and ammonia assimilation by anaerobic continuous cultures of Escherichia coli. Journal of General Microbiology, 85 (1), 11-22. (doi:10.1099/00221287-85-1-11).

Abstract

Anaerobic continuous cultures of E. coli strains HfrC and K12 OR75 assimilated nitrite to produce 63.7 g dry mass/g atom N. Washout occurred when these cultures were aerated, or when the dilution rate was above 0.05 hr^-1. Nitrite reductase, glutamate dehydrogenase and glutamine synthetase activities and cytochrome C₅₅₂ synthesis were depressed when growth of strain OR75 was limited by concentration of either nitrite or ammonia in the reservoir. Glutamate synthase activity was far less than glutamate dehydrogenase, but was highest when nitrite limited growth. These results indicate that enzymes which catalyse glutamate synthesis from inorganic nitrogen compounds are regulated in an interdependent manner, but that glutamine synthetase protein is unlikely to be the aporepressor for glutamate dehydrogenase synthesis in this organism. Possible reasons for apparently opposite regulatory mechanisms in E. coli and Klebsiella aerogenes are discussed in the context of the selective pressures which are applied to bacteria in continuous culture. It is concluded that E. coli K12 has alternative pathways for synthesizing glutamate, and because the Km of glutamate dehydrogenase for NH₃ is 1.6 mM, a growth limiting concentration of an inorganic nitrogen compound in the reservoir would be assimilated predominantly by the glutamine synthetase glutamate synthase pathway.

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Contributors

Author: C. W. Keevil

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