Characterization of the ferrioxamine uptake system of Nitrosomonas europaea

摘要

The chemolithoautotroph Nitrosomonas europaea has two genes predicted to encode outer-membrane (OM) ferrioxamine transporters. Expression of the ferrioxamine uptake system required induction, as shown by the shorter lag phase in ferrioxamine-containing cultures when ferrioxamine-exposed cells were used as an inoculum. The two OM ferrioxamine siderophore transporters encoded by foxA1(NE1097) and foxA2(NE1088) were produced only in cells grown in Fe-limited ferrioxamine-containing medium. The inactivation of foxA1, singly or in combination with foxA2, prevented growth in Fe-limited medium containing excess desferrioxamine (DFX). The foxA2-disrupted single mutant grew poorly in the regular Fe-limited (0.2?μM) medium with 10?μM DFX, but grew well when the Fe level was raised to 1.0?μM with 10?μM DFX. For efficient acquisition of Fe-loaded ferrioxamine, N. europaea needs both ferrioxamine transporters FoxA1 and FoxA2. FoxA1 probably regulates its own production, and it controls the production of FoxA2 as well.