BIOSTABILITY IN AMMONIUM-LIMITED CULTURES OFEscherichia coliB/r

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Abstract
The possibility of multiple steady-states and their prediction in chemical reactors was established by the pioneering work of Amundson and colleagues. This paper reports on a heretofore unknown type of multiple steady-state in a chemostat (CFSTR) with a pure culture of E. coli B/r growing under ammonium limitation. Two steady-states at dilution rate (0.91 hr−1) near the maximum growth rate (0.94 hr−1) result in residual concentrations of ammonium ion of ca. 40 mg/L and 1.5 mg/L. Dilution rate is the reciprocal of holding time. Models of single cells of E. coli can be used to predict the existence of such multiple steady-states. Ammonium uptake and assimilation both can occur via parallel pathways. The presence of the parallel pathways admits the possibility of this type of multiplicity. The parameters of the ammonium transport mechanism are crucial in allowing multiple steady-states. The model predicts specific growth rates higher than observed in batch culture for the chemostat low residual ammonium steady-state. Data consistent with the prediction of increased maximum specific growth rates is presented.