Figure 2.

Experimental system established for this study. We constructed three isogenic mutant strains of P. stutzeri A1501 that differ in their ability to consume nitrate (NO₃⁻) and nitrite (NO₂⁻) as terminal electron acceptors. Strain A1601 completely consumes nitrate to dinitrogen gas (N₂), strain A1602 has a loss-of-function deletion in the nar gene cluster and cannot consume nitrate and strain A1603 has a loss-of-function deletion in the nir gene cluster and cannot consume nitrite. Definitions: Nar, nitrate reductase encoded by the nar gene cluster; Nir, nitrite reductase encoded by the nir gene cluster; Nor, nitric oxide (NO) reductase encoded by the nor gene cluster; and Nos, nitrous oxide (N₂O) reductase encoded by the nos gene cluster. Arrows indicate the metabolic steps that each strain can perform.