Figure 2.

Effect of nitrite (NO₂^–) on strains sensitive to nitrosative stress. (A) Strain RK4353 (ytfE⁺) or JCB5211 (RK4353 ΔytfE) was transformed with the reporter plasmid pNF383 and grown in duplicate anaerobic cultures. When OD_650 nm reached 0.2, one culture was treated with 2.5 mM NaNO₂, and the other served as a control. Samples were assayed for β-galactosidase activity at the times indicated. β-Galactosidase activity was significantly (p = 0.0062) higher in response to nitrite in RK4353 (ytfE⁺) than JCB5211 (RK4353 ΔytfE). Error bars indicate standard deviation (n = 4) from biological replicates. (B) Strains JC5280 (ΔytfE) and JCB5270 (ytfE⁺), which both lack nitrate and nitrite reductases and NO-consuming enzymes, were grown in the presence (red line) or absence (black line) of 1 mM NaNO₂ and growth was monitored (OD_650 nm) for ∼6 h post addition. (C) Strain JC5280 (ΔytfE) (triangles) or JC5270 (ytfE⁺) (circles) transformed with pBB2016, a ytfE expression plasmid, in the presence (red line) or absence (black line) of 1 mM NaNO₂. The OD_650 nm of samples removed at intervals was determined. The arrow indicates nitrite-induced change in growth. Growth curves were repeated at least twice on different days with different inoculum and medium batches. Representative results from single experiments are shown.