Abstract
SummaryThe Escherichia coli marRAB operon is a paradigm for chromosomally encoded antibiotic resistance. The operon exerts its effect via an encoded transcription factor called MarA that modulates efflux pump and porin expression. In this work, we show that MarA is also a regulator of biofilm formation. Control is mediated by binding of MarA to the intergenic region upstream of the ycgZ‐ymgABC operon. The operon, known to influence the formation of curli fibres and colanic acid, is usually expressed during periods of starvation. Hence, the ycgZ‐ymgABC promoter is recognised by σ38 (RpoS)‐associated RNA polymerase (RNAP). Surprisingly, MarA does not influence σ38‐dependent transcription. Instead, MarA drives transcription by the housekeeping σ70‐associated RNAP. The effects of MarA on ycgZ‐ymgABC expression are coupled with biofilm formation by the rcsCDB phosphorelay system, with YcgZ, YmgA and YmgB forming a complex that directly interacts with the histidine kinase domain of RcsC.
Highlights
The Escherichia coli multiple antibiotic resistance locus was discovered as a genetic element providing resistance to tetracycline (George and Levy, 1983)
The Escherichia coli marRAB operon is a paradigm for chromosomally encoded antibiotic resistance.The operon exerts its effect via an encoded transcription factor called MarA that modulates efflux pump and porin expression
We show that MarA is a regulator of biofilm formation
Summary
The Escherichia coli multiple antibiotic resistance (mar) locus was discovered as a genetic element providing resistance to tetracycline (George and Levy, 1983). The region encodes an operon designated marRAB and provides resistance to quinolones, β-lactams and a range of phenolic compounds (George and Levy, 1983; Ariza et al, 1994; White et al, 1997). The ability of the operon to provide resistance against antimicrobial compounds is dependent on marA that encodes a transcriptional activator (Ariza et al, 1994; Rhee et al, 1998). MarA plays an important role in drug resistance by activating the expression of the acrAB-tolC encoded efflux pump (White et al, 1997; Zhang et al, 2008)
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