FIG. 1.

P. aeruginosa biofilms require more iron for maximal catalase activity. (A) Comparison of catalase activities in biofilms (○) and stationary-phase planktonic cultures (●) grown in the presence of the iron-specific chelator 2,2-dipyridyl, without added iron, or with increasing iron concentrations. Catalase activity is shown as units of activity per milligram of protein, where 1 U is defined as the amount which decomposes 1 μmol of H₂O₂ min⁻¹. Error bars, where visible, represent ±1 standard error of the mean for three separate cultures. (B) SOD activity stain of planktonic and biofilm whole-cell proteins (50 μg per lane) resolved in a native gel. The locations of the isozymes Mn-SOD and Fe-SOD are designated to the left of the gel image. Total protein concentration was determined using a Bio-Rad protein assay kit with bovine serum albumin fraction V as a standard.