The outer membrane (OM) protein profile of grown in an iron rich chemically defined medium (Fe + CDM) showed three major proteins of 32.5, 35.5 and 39.0 kDal. The 35.5 and 39.0 kDal proteins were non-covalently associated with peptidoglycan. At least six new iron regulated outer membrane proteins (IRMP) of 69, 70, 73, 75, 78 and 83 kDal, which were not peptidoglycan associated, were apparent in the OM of grown in iron restricted (serum) or iron deficient (Fe-CDM) media. An 18.5 kDal protein was also present in the OM of stationary phase following growth in Fe + CDM, in iron saturated serum and in citrate supplemented CDM but was repressed in Fe-CDM or in serum. Enterochelin but not aerobactin was detected in the spent supernates of iron deficient Inoculation of iron replete into low iron CDM (≤17 × 10 -Fe) produced IRMP and enterochelin within two generations, and several generations before the end of exponential phase. Inoculation of iron depleted cells into Fe + CDM resulted in dilution rather than active excretion from the OM of the IRMP, 1.5 generations being required for the initial level to decrease by one-half and 4 generations for it to return to that observed after growth to stationary phase in Fe + CDM. The appearance of the IRMP of grown under iron depletion was unaffected by prior growth of the inoculum in a gross excess of iron which suggested that whether or not was capable of storing iron, it rapidly responded to the extracellular iron concentration.


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