Detection and automatic control of ammonium ion concentration in miceobial culture with an ammonium ion selective electrode

Abstract

An ammonium ion selective electrode (AISE) had a membrane of polyvinyl chloride in which the antibodies nonactin and monacin were embedded. The detection range was 0.1–200 mM. The step response was 90% in 20 seconds. The output of the AISE increased 6% with a 1°C rise temperature. The output of the AISE was constant between pH 4–7. The selectively coefficient of potassium ion was 0.158 and hence its interferring effect must be considered. The selectivity coeficcients of other cations were small enough to be negligible. Throughout a batch culture of Escherichia coli, values calculated by subtrating (selectivity coefficient) × (potassium ion concentration) from the detected output of the AISE agreed with actual concentrations of ammonium ion. An automatic. constant-value, feebdack control system of ammonium ion concentration was attempted by on-off controlled supply of solution containing both ammonium and potassium ions, the proportion of whose concentration was made equal to the proportion of their average volumetric consumption rates by a microorganism in batch culture. By this control system, ammonium ion concentrations in culture supernatants of fed-batch cultures of Escherichia coli and Saccharomyces cerevisiae could be maintained vitrually at constant levels (5±0.8 mM for the cultivation of E. coli and 50±5 M for the cultivation of S. cerevisiae).