An autoinducer-independent RhlR quorum-sensing receptor enables analysis of RhlR regulation.

TitleAn autoinducer-independent RhlR quorum-sensing receptor enables analysis of RhlR regulation.
Publication TypeJournal Article
Year of Publication2019
AuthorsMcCready, AR, Paczkowski, JE, Cong, J-P, Bassler, BL
JournalPLoS Pathog
Volume15
Issue6
Paginatione1007820
Date Published2019 Jun
ISSN1553-7374
Abstract

Quorum sensing is a chemical communication process that bacteria use to coordinate group behaviors. Pseudomonas aeruginosa, an opportunistic pathogen, employs multiple quorum-sensing systems to control behaviors including virulence factor production and biofilm formation. One P. aeruginosa quorum-sensing receptor, called RhlR, binds the cognate autoinducer N-butryl-homoserine lactone (C4HSL), and the RhlR:C4HSL complex activates transcription of target quorum-sensing genes. Here, we use a genetic screen to identify RhlR mutants that function independently of the autoinducer. The RhlR Y64F W68F V133F triple mutant, which we call RhlR*, exhibits ligand-independent activity in vitro and in vivo. RhlR* can drive wildtype biofilm formation and infection in a nematode animal model. The ability of RhlR* to properly regulate quorum-sensing-controlled genes in vivo depends on the quorum-sensing regulator RsaL keeping RhlR* activity in check. RhlR is known to function together with PqsE to control production of the virulence factor called pyocyanin. Likewise, RhlR* requires PqsE for pyocyanin production in planktonic cultures, however, PqsE is dispensable for RhlR*-driven pyocyanin production on surfaces. Finally, wildtype RhlR protein is not sufficiently stabilized by C4HSL to allow purification. However, wildtype RhlR can be stabilized by the synthetic ligand mBTL (meta-bromo-thiolactone) and RhlR* is stable without a ligand. These features enabled purification of the RhlR:mBTL complex and of RhlR* for in vitro examination of their biochemical activities. To our knowledge, this work reports the first RhlR protein purification.

DOI10.1371/journal.ppat.1007820
Alternate JournalPLoS Pathog.
PubMed ID31194839
PubMed Central IDPMC6564026