Phosphorylation and dephosphorylation at Ser-46 in HPr, a phosphocarrier protein of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) is controlled by the bifunctional HPr kinase/phosphorylase (HprK/P). In Gram-positive bacteria, P-Ser-HPr controls (1) sugar uptake via the PTS; (2) catabolite control protein A (CcpA)-mediated carbon catabolite repression, and (3) inducer exclusion. Genome sequencing revealed that HprK/P is absent from Gram-negative enteric bacteria, but present in many other proteobacteria. These organisms also possess (1) HPr, the substrate for HprK/P; (2) enzyme I, which phosphorylates HPr at His-15, and (3) one or several enzymes IIA, which receive the phosphoryl group from P∼His-HPr. The genes encoding the PTS proteins are often organized in an operon with hprK. However, most of these organisms miss CcpA and a functional PTS, as enzymes IIB and membrane-integrated enzymes IIC seem to be absent. HprK/P and the rudimentary PTS phosphorylation cascade in Gram-negative bacteria must therefore carry out functions different from those in Gram-positive organisms. The gene organization in many HprK/P-containing Gram-negative bacteria as well as some preliminary experiments suggest that HprK/P might control transcription regulators implicated in cell adhesion and virulence. In α-proteobacteria, hprK is located downstream of genes encoding a two-component system of the EnvZ/OmpR family. In several other proteobacteria, hprK is organized in an operon together with genes from the rpoN region of Escherichia coli (rpoN encodes a σ54). We propose that HprK/P might control the phosphorylation state of HPr and EIIAs, which in turn could control the transcription regulators.

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Bacterial surface-associated proteins play crucial roles in host-pathogen interactions and pathogenesis. The identification of these proteins represents an important goal of bacterial proteomics for vaccine development, but also for environmental concerns such as microbial biosensing. Here, we developed such an approach for Legionella pneumophila, a bacterium that causes severe pneumonia. We propose a complementary strategy consisting of (1) a fluorescent labelling of surface-exposed proteins in parallel with (2) a fractionation of the outer-membrane protein extract. These two distinct protein populations were subsequently separated using two-dimensional gel electrophoresis and characterised by mass spectrometry. Within these populations, we found proteins which were expected for the compartments studied, but also a great number of proteins never experimentally described, and also a non-negligible fraction of proteins never described in these fractions. These data provided new routes of inspection for transport and host recognition for Legionella pneumophila. In addition, these results on the membranome and surfaceome show that Legionella in the stationary phase of growth possesses the major determinants to infect host cells.

Better understanding of uranyl toxicity in bacteria is necessary to optimize strains for bioremediation purposes or for using bacteria as biodetectors for bioavailable uranyl. In this study, after different steps of optimization, Escherichia colicells were exposed to uranyl at low pH to minimize uranyl precipitation and to increase its bioavailability. Bacteria were adapted to mid acidic pH before exposure to 50 or 80 µM uranyl acetate for two hours at pH≈3. To evaluate the impact of uranium, growth in these conditions were compared and the same rates of cells survival were observed in control and uranyl exposed cultures. Additionally, this impact was analyzedby two-dimensional differential gel electrophoresis proteomics to discover protein actors specifically present or accumulated in contact with uranium.Exposure to uranium resulted in differential accumulation of proteins associated with oxidative stress and in the accumulation of the NADH/quinone oxidoreductase WrbA. This FMN dependent protein performs obligate two-electron reduction of quinones, and may be involved in cells response to oxidative stress. Interestingly, this WrbA protein presents similarities with the chromate reductase from E. coli, which was shown to reduce uranyl in vitro.