FIG 7.

MdrR1 and MdrR2 regulate biofilm formation through the phz2 operon. (A) Various mutant strains of phz2 genes regulated by MdrR1 and MdrR2 have decreased biofilm formation. A biofilm assay was performed in triplicate, and average amounts of biofilm and standard errors of the means are shown. (B) Model of the MdrR1 and MdrR2 regulatory network summarizing the genes that they control. Heat maps display the spatial expression patterns of these genes summarized by using data from a previous study (38). Fold changes of spatially expressed genes are shown with a red-black-green double-color gradient. Green indicates upregulation and red indicates downregulation compared to levels under planktonic growth conditions, as shown in the color gradient bar (log₂ fold change, 2 to −2). For each location within the biofilm, the box represents the average fold change of data from three biological replicates. MdrR1 and MdrR2 were shown to repress one multidrug efflux pump (MexAB-OprM) while activating another (EmrAB). Additionally, MdrR1 and MdrR2 act together as an activator for a phenazine biosynthesis operon, phz2, and PA3462, a probable sensor/response regulator hybrid.