Ferrous and ferrichrome iron transport and regulation system in the photosynthetic bacterium R. ubrivivax gelatinosus

Abstract

Iron is an essential redox component of most of the living organisms. It is particularly important for photoautotrophs since iron is a crutial part of many proteins involved in the electron transfer process. Despite its crucial role in photosynthesis almost nothing is known on the iron acquisition in these organisms, and no details are available on the molecular basis of the transport system(s). Here we report the identification of four genes (fitQRSA) involved in ferrous and ferrichrome iron acquisition in R. gelatinosus. fitQ and fitA show significant similarities to the ferrichrome receptor (fhuA) from E. coli. Unlike the E. coli fhuA, the R. gelatinosus fitQA are flanking the fitRS genes that show significant similarities to the ferric dicitrate regulatory genes fecIR from E. coli. fitR encode a Fur-regulated ECF sigma factor while fitS encode the transmembrane sensor. fitRSA expression is iron-regulated and is induced upon iron starvation as shown by the m me iron uptake. Moreover, no induction was obtained in the fitQ null mutant, suggesting that FitQ receptor is also requiered for the signal transduction under iron limiting conditions. These results provide the first molecular insight into iron transport by phototrophic bacteria, and a model addressing iron transport in R. gelatinosus is discussed.