Summary: The function of Ca in a psychrophilic Achromobacter, previously found to bind large amounts of these ions to its envelope, has been studied. Bacteria suspended in media of low ionic content showed decreases in wet weight, dry weight and growth capacity, and increases in light scattering and in the release of u.v.-absorbing substances into the medium. The permeability barrier to Ca was also damaged, and there was a release of radioactivity from bacteria labelled with Ca. These events occurred at the optimum growth temperature, and took place at increased rates at higher temperatures. Damage was prevented to about the same extent by 0.1 mM-CaCl, BaCl or MgCl and by 10 mM-NaCl, KCl or LiCl. Ion competition experiments showed that Ca was preferentially taken up and retained in comparison with Ba, Mg and Na, in that order. Isolated envelopes gave similar results. The dry weight of envelopes was reduced by 35% when they were suspended in water at 40 °C.

It is clear that the function of certain envelope components in Achromobacter is highly dependent on divalent cations; and that both the integrity of the permeability barrier and the stability of the envelope are affected at low ion concentrations.


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