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. 2021 Mar 15;49(7):3981–3996. doi: 10.1093/nar/gkab149

Figure 7.

Figure 7.

The pHNSHP45 plasmid-encoded PcnR protein favours the fitness of bacteria carrying mcr-1-bearing IncI2 plasmids. (A) PcnR enhances the fitness of E. coli BW25113 harbouring pHNSHP45 by repressing the plasmid copy number. pHNSHP45 plasmid is the first discovered mcr-1+-IncI2 plasmid. Deletion of pcnR increases plasmid copy number by 10-fold and largely impairs the growth of the host. Deletion of mcr-1 completely rescues the growth of pcnR– strain, although with high plasmid copy number. Complementation of mcr-1 in E. coli BW25113 harbouring pHNSHP45ΔpcnR confirmed that host bacteria are sensitive to multicopy mcr-1. Complementation of pcnR represses the copy number of pHNSHP45ΔpcnR. Summary: PcnR maintains a balance between the mcr-1 expression level and bacterial fitness by limiting the copy number of the IncI2 plasmid pHNSHP45 to ensure an appropriate expression level of mcr-1. (B) PcnR maintains the plasmid copy number at a single copy by inhibiting the translation of repA. Deletion of pcnR derepresses the expression of repA and leads to the plasmid copy number increase to ∼10 copies.