Energy-independent binding of iron complexed to small organic chelants by Neisseria meningitidis.

Abstract

Fe3+-dicitrate binding and iron uptake from citrate have been characterized in three carrier and three case isolates of Neisseria meningitidis. Culture in Fe3+-dicitrate rich medium did not induce subsequent Fe3+-dicitrate binding as it does for Escherichia coli and other bacteria. Growth in iron-restricted conditions slightly stimulated the Fe3+-dicitrate binding system in all the strains studied. Total binding of citrate as Fe3+-dicitrate was 2.5 times that of citrate in the absence of iron. Affinity for Fe3+-dicitrate ranged from 6.3×104 to 2.6×105l/mol, and the number of receptors per cell ranged from 8, 500 to 64, 800. The binding system was highly specific for Fe3+-dicitrate (it did not bind other iron complexes with isocitrate, lactate, pyruvate or EDDA). Fe uptake efficiency was significatively higher in the case strains but, due to the higher number of receptors per cell in the carrier strains, the resulting iron uptake rate is similar in both groups.