THE GROWTH-PROMOTING EFFECT OF BACTERIAL IRON FOR SERUM-EXPOSED BACTERIA

Abstract

Bacterial ability to obtain Fe in bovine serum or in media containing transferrin (Tr) or conalbumin (Ca) was investigated by using serum-resistant (virulent) and serum-sensitive (avirulent) strains of Escherichia coli and Salmonella typhimurium. Bacteria growing in bovine serum enriched with radioactive Fe-saturated Tr or with radioactive Fe-saturated enterobactin (E) did not acquire radioactive Fe. The passage of siderophore(Si)-Fe complexes into bacteria is blocked in serum by Tr and in Ca-containing medium by Ca. The investigation of bacterial ability to take Fe in synthetic media showed that bacteria taken in Si-bound but not Tr-bound radioactive Fe. In the absence of free Fe, the growth of serum-exposed virulent bacteria was supported by their stored Fe. Virulent bacteria passaged in medium void of usable Fe became depleted in stored Fe and did not grow in animal sera unless sera were enriched by the addition of exogenous Fe. Experiments with serum-exposed avirulent bacteria showed that their growth in Si-enriched serum should not be attributed to the Fe-providing activity of Si but to the stimulating effect of Si which facilitates the use of stored Fe. As distinct from avirulent bacteria, virulent bacteria used stored Fe without the stimulating activity of extracellular Si.