Divalent cations in the envelope of a psychrophilic Achromobacter

The function of Ca2+ 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 Ca2+ was also damaged, and there was a release of radioactivity from bacteria labelled with 45Ca2+. 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-CaC12, BaC12 or MgC12 and by 10 mM-NaC1, KC1 or LiC1. Ion competition experiments showed that Ca2+ was preferentially taken up and retained in comparison with Ba2+, Mg2+ 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 degrees 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.