Characterizing the nitrate reduction pathway in C. ljungdahlii. (A) Pathway map of the reconstructed nitrate reduction pathway with the respective genes associated to the reactions. Inset shows the differential expression of the genes in the nitrate reduction pathway under ammonium-free medium with nitrate compared to nitrate-free medium with ammonium as the nitrogen source. Reaction abbreviations: NO3t2 (nitrate transporter), NO2t2r (nitrite transporter), NTRARf (nitrate reductase), NTRIR5 (nitrite reductase), HAMR (hydroxylamine reductase), NH4t (ammonium transporter). (B) Physiological data when C. ljungdahlii is grown on fructose in ammonium-free media with nitrate as the nitrogen source. Purple line represents fructose, green line represents OD600, brown line represents acetate, red line represents nitrate and orange line represents ammonia measurements respectively.