An Endogenously Produced Substance Essential for Growth Initiation of Pasteurella tularensis

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Abstract
Material produced by growing P. tularensis and required for the initiation of growth of P. tularensis from small inocula (growth-initiating substance, GIS) was purified by Sephadex gel filtration and ion-exchange resin chroma-tography. The purified material was characterized as an anionic compound of low molecular weight, heat-stable at neutral pH and in dilute alkali but destroyed by heating in dilute acid. Out of large variety of known nutrients tested, only iron salts and some iron-chelating compounds (sideramines) replaced partially GIS in supporting growth of different P. tularensis strains from small inocula. GIS formed complexes with iron and copper ions. The production of GIS by P. tularensis in a chemically defined medium was enhanced by added ornithine. Isotopic evidence established the role of ornithine as a biosynthetic precursor of GIS.