On the other hand, in the magnetotactic Magnetovibrio blakemorei strain MV-1 which is capable of anaerobic respiration with N2O as electron acceptor, a putative periplasmic Fe (II) oxidase was identified and proposed as N2O reductase NosZ [35], which suggests that N2O reductase might be also involved in magnetite biomineralization by unknown functions. In addition,
in ΔMgfnr BB-94 mutant the different phenotypes observed under anaerobic and microaerobic conditions in the presence of nitrate indicate that MgFnr plays a more important role in magnetite biomineralization when O2 respiration and denitrification occur simultaneously. Necrostatin-1 concentration Our recent findings showed that maintaining a balance between aerobic respiration and denitrification is crucial for WT-like magnetite biomineralization [34]. In this case, MgFnr might provide the
main contribution to mediate the expression of denitrification genes and therefore, poise the redox state for magnetosome formation. Since deletion of Mgfnr altered oxygen-dependent regulation Cell Cycle inhibitor of denitrification genes under aerobic conditions, we hypothesized that MgFnr protein is active under aerobic conditions. Consistent with this, the expression of Mgfnr was upregulated by oxygen, which, however, was never reported for any Fnr protein from other bacteria. Studies on EcFnr mutants in E. coli have established the important role of a [4Fe-4S]2+ cluster in regulating EcFnr activity, and some single amino acid substitutions at positions not conserved in the Fnr family led to increased stability of Fnr to oxygen and activated transcription of nitrate reductase genes under aerobic growing conditions Florfenicol [24, 25, 30, 32, 36]. None of these
reported amino acids of EcFnr are conserved in MgFnr, which might cause a more active MgFnr under aerobic conditions. Among them, Asn-27 and Ile-34 of MgFnr are located very closely to Cys-28 and Cys-37, two of the four cysteine residues that bind the [4Fe-4S]2+ cluster [37, 38]. An E. coli EcFnr mutant protein containing amino acid substitution at either of these two positions showed increased expression of an EcFnr-dependent lac promoter under aerobic conditions [30, 32, 36]. In agreement with these observations, MgFnr mutants including N27D and I34L showed increased aerobic expression of nosZ promoter, suggesting that Asn-27 and Ile-34 of MgFnr are required for a functional MgFnr and likely play a role in maintaining the stability of [4Fe-4S]2+ cluster. However, MgFnr was able to complement ΔEcfnr mutant back to WT-like growth, which indicates that MgFnr also has the universal properties of EcFnr.