Therefore, we first asked if transcription of the Mgfnr gene itself is under oxygen-dependent regulation. WT cells expressing Mgfnr-gusA showed the lowest β-glucuronidase activity under microaerobic conditions in the absence of nitrate, while the presence of nitrate

RG7420 price slightly increased microaerobic check details expression of Mgfnr (Figure 4B). The expression of Mgfnr was induced approximately 4-fold in the presence of nitrate and more than 2-fold in the absence of nitrate under aerobic conditions relative to microaerobic conditions, which again suggested that MgFnr is likely active and acts as a repressor under aerobic conditions. In the ΔMgfnr mutant, Mgfnr-gusA also exhibited the highest β-glucuronidase activity under aerobic conditions in the presence of nitrate. However, compared to WT under aerobic conditions, expression levels of Mgfnr in ΔMgfnr mutant were significantly decreased, which indicated that expression of Mgfnr is also probably

autoregulated. However, we failed to observe a putative Fnr binding site in the Mgfnr promoter region, implying other unknown proteins may be involved in the regulation of Mgfnr. MgFnr can complement E. coli ΔEcfnr mutant All previous observations were pointing towards a scenario, in which MgFnr may also repress expression of denitrification genes under aerobic conditions, which however has never been reported for any Fnr protein from other bacteria. Therefore, the question arose as to whether MgFnr is a genuine oxygen-responsive regulator. Consequently, an XAV-939 chemical structure Ecfnr deletion mutant

ΔEcfnr was transcomplemented with Mgfnr. As shown before [11], ΔEcfnr cells displayed deficient anaerobic growth when nitrate was used as the sole electron acceptor on Thalidomide lactate minimal medium, whereas they grew to similar yields as the WT anaerobically growing on glucose medium (Figure 4C). However, in the ΔEcfnr + pLYJ132 strain which contained the WT-Mgfnr gene, anaerobic growth in the presence of nitrate was restored back to E. coli WT-like level, which demonstrated that MgFnr is also functional in E. coli. Vice versa, the MSR-1 ΔMgfnr strain containing Ecfnr gene (ΔMgfnr + pLYJ153) generated N2 bubbles after 24 h (Figure 4A), suggesting that EcFnr also functions in MSR-1. As shown in Figure 2C and Table 1, ΔMgfnr + pLYJ153 strain containing Ecfnr again synthesized WT-like magnetite crystals. Under anaerobic conditions, overexpression of EcFnr resulted in a decrease in crystals size as overexpression of MgFnr does (Table 1, Additional file 1). However, when EcFnr was overexpressed in MSR-1 WT under microaerobic conditions, magnetite crystals with WT size were formed, contrary to what was observed with overexpression of MgFnr.