Iron uptake in colicin B-resistant mutants of Escherichia coli K-12.

Four classes of colicin B-resistant mutants of Escherichia coli K-12 were examined for defects in iron uptake. All four mutant classes (cbt, exbC, exbB, and tonB) were defective in the uptake of ferri-ennterochelin. The tonB mutant was also defective in citrate-, ferrichrome-, and rhodoturulic acid-mediated iron uptake. The defects in iron transport were reflected in increased sensitivity to iron chelators and to chromium and aluminium salts, and in hypersecretion of enterochelin. One of the mutants (cbt) was apparently defective in outer membrane ferri-enterochelin receptor activity. aroE derivatives (unable to synthesize enterochelin) of the four mutant classes and the parent strain produced increased amounts of two outer membranes polypeptides when grown under iron stress. These polypeptides are implicated in ferri-enterochelin receptor activity.