title: Replacement of potassium ions by ammonium ions in different micro-organisms grown in potassium-limited chemostat culture.
abstract: The biomass concentration extant in potassium-limited 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 evident 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 NH4+, a proposition consistent with the close similarity of the ionic radii of the potassium ion (1.33 A) and the ammonium ion (1.43 A). 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 potassium-limited medium containing initially 0.5 mM K+.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Microbiology, University of Amsterdam, The Netherlands.
authors.forename: E T
authors.initials: ET
authors.lastname: Buurman
authors.forename: J
authors.initials: J
authors.lastname: Pennock
authors.forename: D W
authors.initials: DW
authors.lastname: Tempest
authors.forename: M J
authors.initials: MJ
authors.lastname: Teixeira de Mattos
authors.forename: O M
authors.initials: OM
authors.lastname: Neijssel
mesh_terms: D003470:Culture Media; D001411:Geobacillus stearothermophilus / Q000254:growth & development*; D006863:Hydrogen-Ion Concentration; D007711:Klebsiella pneumoniae / Q000254:growth & development*; D011188:Potassium / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
chemical_list: D003470:Culture Media; D000644:Quaternary Ammonium Compounds; D011188:Potassium