Additional file 8: Figure S2. Analysis of resazurin specificity. Multiple oxygen gradients were prepared using M9 minimal medium (A) or LB (B), with agarose concentrations of 1, 2, 3, 4, 5, or 6 g/l. The concentration of dissolved oxygen was determined in mg/l using a micro-electrode. The micro-electrode was moved from high to low oxygen levels by 1 mm/min to ensure stabilization of both the readings and the gradient. The readings were compared to the colour of the resazurin to determine its specificity. The dashed purple line indicates the resazurin colour turning point from pink to colourless.