Gray boxes indicate DNA-binding motif. Single residue changes which are capable to activate transcription of nitrate

reductase genes under aerobic conditions in E. coli are shown in red. Amb4369 is from M. magneticum strain and Magn03010404 is from M. magnetotacticum. We constructed Selleckchem Anlotinib an Epoxomicin purchase unmarked ΔMgfnr mutant by a modified cre-lox based technique as described previously [29]. In both microaerobic ammonium medium and anaerobic nitrate medium, ΔMgfnr mutant cells displayed WT-like growth and magnetic response (Cmag) (data not shown) and produced WT-like magnetosome crystals (Figure 2A and B) with similar crystal size (40.2 ± 15.3 nm versus 38.0 ± 15.8 nm in WT under anaerobic conditions; 30.0 ± 13.6 nm versus 29.9 ± 14.5 nm in WT in microaerobic ammonium medium). However, although the ΔMgfnr mutant grew as the WT in microaerobic nitrate medium, Cmag values were slightly lower than those in the WT during the entire growth (Figure 3). In agreement with this, ΔMgfnr mutant cells contained smaller and aberrantly shaped particles in addition to particles with a WT-like size and appearance (Table 1, Figure 2B). Transcomplementation of ΔMgfnr strain with the WT allele (ΔMgfnr + pLYJ110) restored magnetosome formation back to the WT level with similar crystal size (Figure 2C, Table 1). However, WT overexpressing

Mgfnr (WT + pLYJ110) produced smaller magnetite particles Caspase Inhibitor VI mouse under anaerobic conditions (30.3 ± 15.1 nm, which was similar

to that of WT in microaerobic nitrate medium) (Table 1, Additional file 1) and also under microaerobic conditions in the presence of nitrate (23.5 ± 13.8 nm versus 30.5 ± 12.4 in WT). This indicated that MgFnr is involved in magnetosome formation during nitrate reduction, and that the expression level of MgFnr is crucial for proper magnetite biomineralization. Figure 2 Effects of Mgfnr deletions on magnetosome formation. (A) Left: TEM images of whole cells of WT (from top to bottom) in anaerobic nitrate medium, microaerobic ammonium medium, and microaerobic nitrate medium. Bar, 500 nm. Right: Closeup views of magnetosome crystals shown on the left. Bar, 100 nm. (B) Left: TEM images of whole cells of ΔMgfnr mutant (from top to bottom) in anaerobic nitrate medium, Exoribonuclease microaerobic ammonium medium, and microaerobic nitrate medium. Bar, 500 nm. Right: Closeup views of magnetosome crystals shown on the left. Irregular shaped particles are indicated by black arrows. Bar, 100 nm. (C) Left: TEM images of ΔMgfnr mutant complemented with plasmids pLYJ110 harboring Mgfnr gene and pLYJ153 harboring Ecfnr gene in microaerobic nitrate medium. Bar, 500 nm. Right: Closeup views of magnetosome crystals shown on the left. Bar, 100 nm. Figure 3 Time courses of nitrate and nitrite utilization during microaerobic growth of WT and Δ Mgfnr mutant in nitrate medium.