Fig. 4

Swarming motility of the P. aeruginosa MrpA and Complex I mutants compared to the wild-type strain (WT). The swarming motility was accessed after 18 h on semi-solid agars of pH 6.5, 7.5, or 8.5 and no additional NaCl or when supplemented with 400 mM NaCl. Swarming motility was measured as area of growth with the software ImageJ and graphed as square-pixels. Representative photographs are shown in Fig. 5. No statistical differences were observed at acidic pH (panel a). At pH 7.5 and without added sodium, the Complex I mutant showed significantly reduced swarming motility in compare to WT (p < 0.0001) while the Mrp mutant but not the Complex mutant showed hypomotility when 400 mM NaCl was added (panel b). Very little swarming motility was detected at pH 8.5 (panel c), with significant hypermotility of the Complex I mutant when no sodium was added p < 0.0001), but reduced swarming of the Mrp mutant (p < 0.001). When at pH 8.5 (panel c), 400 mM NaCl was added, the Mrp mutant did not grow on the semi-solid agar (see Fig. 5), and the Complex I mutant revealed significantly reduced swarming motility in compare to WT (both p < 0.0001)