Pseudomonas aeruginosa biofilm matrix polysaccharide Psl is regulated transcriptionally by RpoS and post‐transcriptionally by RsmA

Abstract

Extracellular polysaccharides are important components of biofilms. In non-mucoid Pseudomonas aeruginosa strains, the Pel and Psl polysaccharides are major structural components of the biofilm matrix. In this study, we demonstrate that the alternative σ-factor RpoS is a positive transcriptional regulator of psl gene expression. Furthermore, we show that psl mRNA has an extensive 5′ untranslated region, to which the post-transcriptional regulator RsmA binds and represses psl translation. Our observations suggest that upon binding RsmA, the region spanning the ribosome binding site of psl mRNA folds into a secondary stem-loop structure that blocks the Shine–Dalgarno sequence, preventing ribosome access and protein translation. This constitutes a novel mechanism for translational repression by this family of regulators.

Importance of positioning for microbial evolution

“…RsmE is one of three Rsm proteins in the Pf0-1 genome. Among the pseudomonads, Rsm proteins are known to promote motility (28) and suppress various secreted products, such as protease, extracellular polysaccharides, and a quorum-sensing system that regulates phenazine biosynthesis (25,(29)(30)(31). Given the nature of such components, the Gac/Rsm regulatory cascade has previously been proposed as a key modulator of bacterial social behavior (25).…”

“…This finding supports the notion that the original mutation in the MV results in loss of RsmE function and is sufficient to cause the MV phenotype. Note that RsmE is a global repressor, so although the mutations cause a loss of function at the level of RsmE, the dominant phenotypic outcome is predicted to be an increase in multiple types of secretion under the control of the Gac/Rsm regulatory cascade (25,(29)(30)(31).…”

Sticky Situations: Key Components That Control Bacterial Surface Attachment

“…Ultimately, this system controls attachment and virulence via the CsrA homolog RsmA (18). While RsmA is thought to elevate type III secretion system (TTSS) transcript abundance, binding of RsmA to the 5= untranslated region of psl mRNA was recently shown to prevent ribosome access and protein translation (66). In P. aeruginosa, RsmA function is antagonized by the sRNAs rsmZ and rsmY, whose expression is directly controlled by GacA/GacS, the TCS homolog of the E. coli BarA/UvrY system (reviewed in reference 107).…”

“…For instance, the sigma factor RpoS is a positive regulator of psl gene expression in P. aeruginosa (66), yet inactivation of rpoS has been correlated with more-substantial biofilm biomass accumulation compared to that of the wild type (59). Similarly, P. aeruginosa rpoN mutants are capable of forming biofilms but are impaired in attachment while demonstrating in-creased production of sadB, which is essential for attachment (20,57,143,151).…”

Self-produced exopolysaccharide is a signal that stimulates biofilm formation inPseudomonas aeruginosa

“…Binding of c-di-GMP by PelD, a protein in the Pel biosynthetic complex, is also required for Pel biosynthesis (11). Additionally, the transcriptional repressor RsmA regulates translation of the psl transcript (12).…”