The Gac-Rsm and SadB Signal Transduction Pathways Converge on AlgU to Downregulate Motility in Pseudomonas fluorescens

Flagella mediated motility in Pseudomonas fluorescens F113 is tightly regulated. We have previously shown that motility is repressed by the GacA/GacS system and by SadB through downregulation of the fleQ gene, encoding the master regulator of the synthesis of flagellar components, including the flagellin FliC. Here we show that both regulatory pathways converge in the regulation of transcription and possibly translation of the algU gene, which encodes a sigma factor. AlgU is required for multiple functions, including the expression of the amrZ gene which encodes a transcriptional repressor of fleQ. Gac regulation of algU occurs during exponential growth and is exerted through the RNA binding proteins RsmA and RsmE but not RsmI. RNA immunoprecipitation assays have shown that the RsmA protein binds to a polycistronic mRNA encoding algU, mucA, mucB and mucD, resulting in lower levels of algU. We propose a model for repression of the synthesis of the flagellar apparatus linking extracellular and intracellular signalling with the levels of AlgU and a new physiological role for the Gac system in the downregulation of flagella biosynthesis during exponential growth

The aliphatic amidase AmiE is involved in regulation of Pseudomonas aeruginosa virulence

© The Author(s) 2017.We have previously shown that the eukaryotic C-type natriuretic peptide hormone (CNP) regulates Pseudomonas aeruginosa virulence and biofilm formation after binding on the AmiC sensor, triggering the amiE transcription. Herein, the involvement of the aliphatic amidase AmiE in P. aeruginosa virulence regulation has been investigated. The proteome analysis of an AmiE over-producing strain (AmiE +) revealed an expression change for 138 proteins, including some that are involved in motility, synthesis of quorum sensing compounds and virulence regulation. We observed that the AmiE + strain produced less biofilm compared to the wild type, and over-produced rhamnolipids. In the same line, AmiE is involved in P. aeruginosa motilities (swarming and twitching) and production of the quorum sensing molecules N-acyl homoserine lactones and Pseudomonas Quinolone Signal (PQS). We observed that AmiE overproduction reduced levels of HCN and pyocyanin causing a decreased virulence in different hosts (i.e. Dictyostelium discoideum and Caenorhabditis elegans). This phenotype was further confirmed in a mouse model of acute lung infection, in which AmiE overproduction resulted in an almost fully virulence decrease. Taken together, our data suggest that, in addition to its role in bacterial secondary metabolism, AmiE is involved in P. aeruginosa virulence regulation by modulating pilus synthesis and cell-to-cell communication

The opening of the two pores of the Hv1 voltage-gated proton channel is tuned by cooperativity.

In voltage-gated sodium, potassium and calcium channels, the functions of ion conduction and voltage sensing are performed by two distinct structural units: the pore domain and the voltage-sensing domain (VSD). In the hydrogen voltage-gated channel 1 (Hv1), the VSD, unusually, performs both functions. Hv1 was recently found to dimerize and to form channels made of two pores. However, the channels were also found to function when dimerization was prevented, raising a question about the functional role of dimerization. Here we show that the two subunits of the human Hv1 dimer influence one another during gating, with positive cooperativity shaping the response to voltage of the two pores. We also find that the two voltage sensors undergo conformational changes that precede pore opening and that these conformational changes are allosterically coupled between the two subunits. Our results point to an important role for dimerization in the modulation of Hv1 activity