A-NO2−-mediated killing of P. aeruginosa PAO1 under anaerobic conditions. NaNO2 concentrations tested were 0 μg ml−1 (closed circles), 256 μg ml−1 (open circles), 512 μg ml−1 (squares), 1,024 μg ml−1 (triangles), 2,048 μg ml−1 (diamonds), and 4,096 μg ml−1 (stars). The graphs display the averages and standard deviations of three independent cultures analyzed concurrently.