Effect of ammonium ion concentration and osmotic pressure on growth of Ureaplasma urealyticum (T-strain mycoplasma)

Abstract

The effect of NH4+ concentration and osmotic pressure on growth of U. urealyticum type VIII was determined by using a well-buffered broth medium containing 10 mM urea. The addition of NH4Cl to the medium at concentrations up to 10 mM did not affect growth, but addition of larger quantities progressively decreased both the specific growth rate (.mu.) and the maximum yield of the culture, with concentrations of 80 mM completely inhiting growth. Addition of 150 mM KCl or NaCl to the medium did not inhibit growth, indicating that the growth-inhibitory effect was specific to NH4+ and was neither a result of increased Cl- concentration nor increased osmotic pressure. Concentrations of NH4Cl as high as 100 mM did not affect growth of either Acholeplasma laidlawii or Mycoplasma hominis. U. urealyticum was more sensitive to osmotic pressure: osmotic pressures of 710-780 mosmol/kg (with KCl, NaCl or sucrose) resulted in both a substantially lower growth rate and a 5- to 10-fold lower peak yield of organisms. Both A. laidlawii and M. hominis were less sensitive to increased osmotic pressure.