Comparison of iron binding and uptake from FeCl3 and Fe-citrate by Neisseria meningitidis

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Abstract
Fe-starved N. meningitidis SD1C took up Fe added as FeCl3 by a 2-step process: a rapid phase occurring during the 1st min after Fe addition and unaffected by 0.5 mM KCN and a slower secondary phase of uptake sensitive to various metabolic inhibitors. The rate and extent of energy-dependent Fe uptake from stable dicitrate and nitrilotriacetate Fe3+ complexes were essentially identical to FeCl3, indicating the presence of a high-affinity Fe acquisition system. The sulfonated siderophore Desferal (deferrioxamine .beta.-mesylate) effectively prevented any uptake of Fe from the citrate complex and was unable to remove that Fe already bound by either poisoned or active cells. The energy-independent system rapidly deferrated Fe3I+ dicitrate and bound Fe to a finite number of cellular sites. Fe derived from FeCl3 was associated with these same sites and with a large number of apparently nonspecific sites. The extent of low-affinity, nonspecific binding was concentration dependent. Both enenergy-independent and energy-dependent systems involved in the uptake of Fe from the Fe3I+ dicitrate were inactivated by 5 min at 60.degree. C, but not by 45.degree. C. The citrate carrier itself was recycled, being neither bound separately nor in concert with Fe3+ by these sites.