Replacement of potassium ions by ammonium ions in different micro-organisms grown in potassium-limited chemostat culture |
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Authors: | Edward T Buurman Jill Pennock David W Tempest M Joost Teixeira de Mattos Oense M Neijssel |
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Institution: | (1) Department of Microbiology, Biotechnology Centre, University of Amsterdam, P.O. Box 20245, 1000 HE Amsterdam, The Netherlands;(2) Department of Microbiology, University of Sheffield, S10 2TN Sheffield, UK |
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Abstract: | The biomass concentration extant in potassiumlimited cultures of either Klebsiella pneumoniae or Bacillus stearothermophilus (when growing at a fixed temperature and dilution rate in a glucose/ammonium salts medium) increased progressively as the medium pH value was raised step-wise from 7.0 to 8.5. Because the macromolecular composition of the organisms did not vary significantly, this increase in biomass could not be attributed to an accumulation of storage-type polymers but appeared to reflect a pH-dependent decrease in the cells' minimum K+ requirement. Significantly, this effect of pH was not eviden with cultures in which no ammonium salts were present and in which either glutamate or nitrate was added as the sole nitrogen source; however, it was again manifest when various concentrations of NH4Cl were added to the glutamate-containing medium. This suggested a functional replacement of K+ by NH
4
+
, a proposition consistent with the close similarity of the ionic radii of the potassium ion (1.33 Å) and the ammonium ion (1.43 Å). At pH 8.0, and with a medium containing both glutamate (30 mM) and NH4Cl (100 mM), cultures of B. stearothermophilus would grow without added potassium at a maximum rate of 0.7 h-1. Under these conditions the cells contained maximally 0.1% (w/w) potassium (derived from contaminating amounts of this element in the medium constituents), a value which should be compared with one of 1.4% (w/w) for cells growing in a potassiumlimited medium containing initially 0.5 mM K+. Qualitatively similar findings were made with cultures of K. pneumoniae; and whereas one may not conclude that NH
4
+
can totally replace K+ in the growth of these bacteria, it can clearly do so very extensively. |
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Keywords: | Potassium Ammonium Bacillus stearothermophilus Klebstella pneumoniae Chemostat culture Growth requirement-pH |
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