FIG. 4.

The nickel promoter effect in MG1655 ompR234 PHL818 biofilm formation does not rely on the nickel efflux pump RcnA. (A) Biofilm fractions. (B) Planktonic fractions. Growth of MG1655 ompR234 (PHL818; closed symbols) and its rcnA mutant (PHL1374; open symbols) was estimated from the OD₆₀₀ in supernatant and biofilm fractions in 24-well polystyrene plates. The fluorescence of PHL818 harboring the rncA::gfp fusion (PHL1370) was measured in supernatant and biofilm fractions using a spectrofluorimeter, as described in Materials and Methods. Specific activity for GFP fluorescence (dashed lines) was calculated as follows: (GFP fluorescence - initial fluorescence)/OD₆₀₀. If OD₆₀₀ values of one of the fractions were low (below 0.1 U), assays were repeated in petri dishes to collect larger volumes of culture, leading to a more precise quantification of bacterial growth.