• Constitutive production of c-di-GMP is associated with mutations in a variant of Pseudomonas aeruginosa with altered membrane composition.

      Blanka, Andrea; Düvel, Juliane; Dötsch, Andreas; Klinkert, Birgit; Abraham, Wolf-Rainer; Kaever, Volkhard; Ritter, Christiane; Narberhaus, Franz; Häussler, Susanne; Institute for Molecular Bacteriology, TWINCORE,30625 Hannover, Germany. (2015)
      Most bacteria can form multicellular communities called biofilms on biotic and abiotic surfaces. This multicellular response to surface contact correlates with an increased resistance to various adverse environmental conditions, including those encountered during infections of the human host and exposure to antimicrobial compounds. Biofilm formation occurs when freely swimming (planktonic) cells encounter a surface, which stimulates the chemosensory-like, surface-sensing system Wsp and leads to generation of the intracellular second messenger 3',5'-cyclic-di-guanosine monophosphate (c-di-GMP). We identified adaptive mutations in a clinical small colony variant (SCV) of Pseudomonas aeruginosa and correlated their presence with self-aggregating growth behavior and an enhanced capacity to form biofilms. We present evidence that a point mutation in the 5' untranslated region of the accBC gene cluster, which encodes components of an enzyme responsible for fatty acid biosynthesis, was responsible for a stabilized mRNA structure that resulted in reduced translational efficiency and an increase in the proportion of short-chain fatty acids in the plasma membrane. We propose a model in which these changes in P. aeruginosa serve as a signal for the Wsp system to constitutively produce increased amounts of c-di-GMP and thus play a role in the regulation of adhesion-stimulated bacterial responses.
    • The PqsR and RhlR transcriptional regulators determine the level of Pseudomonas quinolone signal synthesis in Pseudomonas aeruginosa by producing two different pqsABCDE mRNA isoforms.

      Brouwer, Stephan; Pustelny, Christian; Ritter, Christiane; Klinkert, Birgit; Narberhaus, Franz; Häussler, Susanne (2014-12)
      Regulation of gene expression plays a key role in bacterial adaptability to changes in the environment. An integral part of this gene regulatory network is achieved via quorum sensing (QS) systems that coordinate bacterial responses under high cellular densities. In the nosocomial pathogen Pseudomonas aeruginosa, the 2-alkyl-4-quinolone (pqs) signaling pathway is crucial for bacterial survival under stressful conditions. Biosynthesis of the Pseudomonas quinolone signal (PQS) is dependent on the pqsABCDE operon, which is positively regulated by the LysR family regulator PqsR and repressed by the transcriptional regulator protein RhlR. However, the molecular mechanisms underlying this inhibition have remained elusive. Here, we demonstrate that not only PqsR but also RhlR activates transcription of pqsA. The latter uses an alternative transcriptional start site and induces expression of a longer transcript that forms a secondary structure in the 5' untranslated leader region. As a consequence, access of the ribosome to the Shine-Dalgarno sequence is restricted and translation efficiency reduced. We propose a model of a novel posttranscriptional regulation mechanism that fine-tunes PQS biosynthesis, thus highlighting the complexity of quorum sensing in P. aeruginosa.