FIG. 3.
Nitrate respiration and denitrification pathways in bacteria. The organization of the anaerobic electron transport chains for nitrate respiration and denitrification is shown at the top. The E. coli respiratory nitrate reductase (nar) gene clusters and the Pseudomonas stutzeri denitrification nos, nir, and nor gene clusters are also shown. Genes are drawn approximately to scale, and arrows show the direction of transcription. The genes and their products are drawn in the same color. Regulatory genes are indicated by black arrows with white vertical lines. The products of the white genes are not shown. The quinone pool is indicated by the white oval labeled QH2⇄Q. cyt, cytochrome.