Coordination of cell envelope biology by Escherichia coli MarA protein potentiates intrinsic antibiotic resistance.

The multiple antibiotic resistance activator (MarA) protein is a transcription factor implicated in control of intrinsic antibiotic resistance in enteric bacterial pathogens. In this work, we screened the Escherichia coli genome computationally for MarA binding sites. By incorporating global maps of transcription initiation, and clustering predicted targets according to gene function, we were able to avoid widespread misidentification of MarA sites, which has hindered prior studies. Subsequent genetic and biochemical analyses identified direct activation of genes for lipopolysaccharide (LPS) biosynthesis and repression of a cell wall remodelling endopeptidase. Rewiring of the MarA regulon, by mutating subsets of MarA binding sites, reveals synergistic interactions between regulatory targets of MarA. Specifically, we show that uncoupling LPS production, or cell wall remodelling, from regulation by MarA, renders cells hypersensitive to mutations altering lipid trafficking by the MlaFEDCB system. Together, our findings demonstrate how MarA co-regulates different aspects of cell envelope biology to maximise antibiotic resistance.