Factors affecting catalase expression in Pseudomonas aeruginosa biofilms and planktonic cells

Previous work with Pseudomonas aeruginosa showed that catalase activity in biofilms was significantly reduced relative to that in planktonic cells. To better understand biofilm physiology, we examined possible explanations fo r the differential expression of catalase in cells cultured in these two di fferent conditions. For maximal catalase activity, biofilm cells required s ignificantly more iron (25 muM as FeCl3,) in the medium, whereas planktonic cultures required no addition of iron. However, iron-stimulated catalase a ctivity in biofilms was still only about one-third that in planktonic cells . Oxygen effects on catalase activity were also investigated. Nitrate-respi ring planktonic cultures produced approximately twice as much catalase acti vity as aerobic cultures grown in the presence of nitrate; the nitrate stim ulation effect could also be demonstrated in biofilms. Cultures fermenting arginine had reduced catalase levels; however, catalase repression was also observed in aerobic cultures grown in the presence of arginine. It was con cluded that iron availability, but not oxygen availability, is a major fact or affecting catalase expression in biofilms.