The chromosomal fur gene regulates the extracellular haemolytic activiy encoded by certain hly plasmids

Abstract

The haemolytic activity encoded by thirteen hly-plasmids of different origin and sources was examined as a function of the Fe 3+-concentration in E. coli fur + and E. coli fur − strains, respectively. In E. coli fur + the relatively low haemolytic activity of five hly-plasmids isolated in Berne and one isolated in Paris was increased significantly under iron-limiting growth conditions. Contrastingly, in E. coli fur − strains containing the same plasmids, a considerably higher amount of secreted haemolysin was detected. This activity could not be further increased by limiting the extracellular iron concentration. Seven other hly-plasmids expressed similar and non-inducible amounts of secreted haemolysin in both E. coli fur + and E. coli fur − strains. These results indicate that the extracellular haemolytic activity encoded by certain hly-plasmids was controlled by the chromosomally encoded fur gene.