SUMMARY: Anaerobic continuous cultures of 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 h. Nitrite reductase, glutamate dehydrogenase and glutamine synthetase activities and cytochrome synthesis were derepressed when growth of strain OR75 was limited by the 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 and are discussed in the context of the selective pressures which are applied to bacteria in continuous culture. We conclude that K12 has alternative pathways for synthesizing glutamate, and because the of glutamate dehydrogenase for NH 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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