Analysis of Δ Mgfnr mutant. (A) N2 production in WT, ΔMgfnr mutant, ΔMgfnr mutant plus pLYJ110, and ΔMgfnr mutant plus pLYJ153 cultures in oxygen gradient tubes with 0.3% agar. ΔMgfnr mutant plus pLYJ110, and ΔMgfnr mutant plus pLYJ153 cells contained respective fnr gene from MSR-1 and E. coli. Gas bubbles were indicated by white arrows. (B) Transcription of Mgfnr promoter fused to gusA in both WT and ΔMgfnr mutant under different conditions. Expression was measured by β-glucuronidase activity. Cultures were grown aerobically or microaerobically in nitrate and ammonium medium. (C) Heterologous transcomplementation of ΔEcfnr mutant harboring the plasmid pLYJ132 which contains Mgfnr. Cultures were anaerobically grown to stationary phase at 30°C in glucose minimal medium (black box) and lactate minimal medium (gray box). (D) Transcription of nosZ fused to gusA in Mgfnr variant strains under aerobic conditions in the presence of nitrate. Expression was measured by β-glucuronidase activity.