Fig. 2.

Nitric oxide plays a critical role in the recovery of Dr growth after UV radiation as monitored by OD₆₀₀. (A) The complementation strain Δnos:pNOS was generated by introducing an IPTG inducible recombinant nos gene on expression plasmid p11530. Cells were grown to OD ≈0.2 and IPTG was added to induce the nos gene until the cell density reached OD ≈1.0 before irradiation. Uninduced Δnos and Δnos:pNOS served as controls. The cell growth (assessed by OD₆₀₀) is shown as mean ± SD relative to irradiated wt cells at 22 h after exposure. The complemented strain grows more slowly than Δnos due to the added pressure of antibiotic selection. (B) Both wt (dark gray bars) and Δnos (light gray bars) cells were grown for 22 h with preincubation (prt) or postincubation (pst) of NO donors (SNP and exogenous NO) and NO scavenger (cPTIO) after 5 min of UV radiation. Control cells were grown in the absence of additive compounds. The relative growth at 22 h after UV was compared to that of wt cells, which were given a value of 100. Inset: Degree of NO rescue by the addition of exogenous NO at various times post irradiation. These values are set relative to the growth of wt cells post-irradiation. The data represents an average of three independent experiments ± SD.