Magnesium-limited Growth of Bacillus subtilis, in Pure and Mixed Cultures, in a Chemostat

Abstract

SUMMARYThe influence of Mg2+-limitation on the growth of a typical Gram-positive organism-Bacillus subtilis-was investigated and the data compared with that obtained with Aerobacter aerogenes grown under similar conditions. The magnesium contents of both organisms varied with growth rate but were very similar at corresponding growth rates. With Mg2+-limited chemostat cultures of each organism, uptake of Mg2+ was almost complete at specific growth rates less than 0.7 x maximum. Cellular Mg2+ was tightly bound, none being removed by suspension of the organisms at 2 0 ' in 0.85 yo (w/v) NaC1. When Mg2+-limited organisms were suspended in environments containing Mg2+, this ion was rapidly adsorbed; the amount adsorbed varied with both the initial extracellular Mg2+ concentration and the composition of the diluent. B. d t i l i s had a greater capacity for Mg2+ adsorption than A . aerogenes but its affinity for this ion was less. The latter difference correlated with the ability of A. aerogenes to outgrow B. subtilis rapidly in Mg2+-limited chemostat cultures containing both organisms. The significance of these results is discussed in relation to the reports from other laboratories concerning differences between Gram-positive and Gram-negative bacteria in Mg2+ content, uptake of Mg2+ and ability to grow in media of low Mg2+ content.

The Influence of Growth-limiting Substrate and Medium NaCl Concentration on the Synthesis of Magnesium-binding Sites in the Walls of Bacillus subtilis var. niger

“…We reported previously (Tempest, Dicks & Meers, 1967) that the affinities with which Bacillus subtilis and Aerobacter aerogenes cell walls bound magnesium ions were different, and that this difference correlated with the ability of the Gram-negative organisms to outgrow the bacilli in Mg2+-limited mixed cultures in a chemostat. The above mentioned adsorption experiments were made with organisms grown in Mg2+-limited culture only; but since the wall composition of organisms is known to vary with the chemical nature of the environment (Ellwood & Tempest, 1967;Tempest, Dicks & Ellwood, I 968), it was of interest to determine whether the affinity with which organisms bound Mg2+ at their surfaces also varied with changes in the nature of the growth limitation.…”

Morphological and Chemical Characteristics of a Cytophaga sp. Grown under Conditions of Magnesium Excess and Magnesium Limitation

“…The continuous culture experiments indicated that Mg2+ content, bacterial dry weight, S-factor production and extracellular carbohydrate, as well as intracellular protein and carbohydrate contents, are all dependent both on the Mg2+ content of the medium and on the growth rate, while the change in RNA content is independent of Mg2+ content and reflects only the bacterial growth rate. A similar series of experiments measuring protein, carbohydrate and RNA content in Klebsiella (Aerobacter) aerogenes and Bacillus subtilis (Tempest et al, 1965(Tempest et al, , 1967 showed the same tendency, but the percentage differences obtained were smaller than those reported here. A change to Mg2+-limited growth results in morphological and chemical changes in Cytophaga sp.…”

The Influence of Extracellular Products on the Behaviour of Mixed Microbial Populations in Magnesium-limited Chemostat Cultures

“…jluorescens have more efficient mechanisms for the uptake of magnesium from their environment than the Gram-positive organisms listed above. It is important to point out that S. epidermidis would grow only in simple salts media that had been supplemented with Casamino acids (I %, w/v) and yeast extract (0.001 %, w/v), each of which contain substances that stimulated growth and the uptake of magnesium by B. subtilis (Tempest et al 1967) and presumably also by the Staphylococcus organisms. Nevertheless, S. epidermidis cultures still were rapidly outgrown by either A. aerogenes or P. fEuorescens organisms.…”

“…Continuous cultures of organisms were maintained in 0.25 1. chemostats (designed by Dr D. Herbert) without pH control. The magnesium-limited medium was basically that described previously (Tempest et al, 1967), but the magnesium content was varied as indicated in the Results section. The potassiumlimited medium was that described by Tempest, Dicks & Hunter (1966)~ but with the potassium concentration decreased to 0-1 5 mM ; the carbon-limited medium was that of Tempest, Hunter & Sykes (1965) but with glucose ( I g./l.)…”

“…The technique for growing mixed cultures of organisms in the chemostat was that described by Tempest et al (1967). For batch culture experiments, 20 ml.…”