A growth initiation factor involved in magnesium utilization by certain soil bacteria

Abstract

Actinomyces humiferus was shown to require relatively high levels of magnesium for growth initiation. This growth initiation response to magnesium was graded. Live, but not heat-killed, cultures of Azotobacter vinelandii cells could replace at least a part of the magnesium requirement when Act. humiferus and Azo. vinelandii were grown together as a dual culture. However, it was necessary that the conditions for the dual culture be such that the Azo. vinelandii cells underwent some lysis. In fact, the initial rate of lysis of the Azo. vinelandii cells was increased in the presence of Act. humiferus, presumably because Act. humiferus was able to remove magnesium from the medium so it was not available to Azo. vinelandii. The magnesium requirement of Act. humiferus for growth initiation could also be replaced by a heat-labile factor found in culture filtrates of Act. humiferus and Azo. vinelandii grown as monocultures and dual cultures. This factor, however, was also present in culture filtrates of Arthrobacter globiformis, Nocardia salmonicolor, and Micrococcus luteus. It was not present in culture filtrates of Escherichia coli, Agromyces ramosus, or Ensifer adhaerens. From these results it appears that several, but not all, bacteria produce a heat-labile factor that is involved in marshalling magnesium for use in growth initiation.