Synechococcus OS-B' , a thermophilic unicellular cyanobacterium, recently isolated from the microbial mats in Octopus Spring (Yellowstone National Park), induces a suite of genes, including phosphatases and transporters, in response to phosphorus (P) starvation. Here we describe two different approaches to examine the ability of Synechococcus OS-B' to synthesize and breakdown polyphosphate (poly P), a key storage compound in many prokaryotes. First, we developed a transformation protocol to create mutants in the polyphosphate kinase (ppk), the major enzyme responsible for the synthesis of poly P. The ppk mutant exhibited a pleiotropic phenotype with defects in poly P accumulation, aberrant levels of pho regulon transcripts, growth defects and changes in cell size and exopolysaccharide levels, among others. Second, we measured transcripts of ppk and ppx (encoding the polyphosphatase) directly from mat samples and found that the levels varied dramatically over a diel cycle. We also used Western blot analysis to quantify levels of PPK and PPX and found that these enzymes differentially accumulated during the diel cycle. Levels of polyphosphate kinase peaked at night, while polyphosphatase levels were highest during the early morning hours. We hypothesize that the opposing activities of these two enzymes allow cells to store and utilize poly P to optimize growth over a diel cycle.

The Escherichia coli regulator MarR represses the multiple antibiotic resistance operon marRAB and responds to phenolic compounds, including sodium salicylate, which inhibit its activity. Crystals obtained in the presence of a high concentration of salicylate indicated two possible salicylate sites, SAL-A and SAL-B. However, it was unclear whether these sites were physiologically significant or were simply a result of the crystallization conditions. A study carried out on MarR homologue MTH313 suggested the presence of a salicylate binding site buried at the interface between the dimerization and the DNA-binding domains. Interestingly, the authors of the study indicated a similar pocket conserved in the MarR structure. Since no mutagenesis analysis had been performed to test which amino acids were essential in salicylate-binding, we examined the role of residues that could potentially interact with salicylate. We demonstrated that mutations in residues shown as interacting with salicylate at SAL-A and SAL-B in the MarR-salicylate structure had no effect on salicylate binding, indicating that these sites were not the physiological regulatory sites. However, some of these residues (P57, R86, M74 and R77) were important for DNA-binding. Furthermore, mutations in residues R16, D26 and K44 significantly reduced binding to both salicylate and 2,4-dinitrophenol, while a mutation in residue H19 impaired the binding to 2,4-dinitrophenol only. These findings indicate, as for MTH313, the presence of a ligand binding pocket located between the dimerization and the DNA-binding domains.

A defining characteristic of biofilms is antibiotic tolerance that can be up to 1,000-fold greater than that of planktonic cells. In P. aeruginosa, biofilm tolerance to antimicrobial agents requires the biofilm-specific MerR-type transcriptional regulator BrlR. However, the mechanism by which BrlR mediates biofilm tolerance has not been elucidated. Genome-wide transcriptional profiling indicated that brlR was required for maximal expression of genes associated with antibiotic resistance, in particular those encoding the multidrug efflux pumps MexAB-OprM and MexEF-OprN. Chromatin immunoprecipitation (ChIP) analysis revealed a direct regulation of these genes by BrlR with DNA binding assays confirming BrlR binding to the promoter regions of the mexAB-oprM and mexEF-oprN operons. qRT-PCR analysis further indicated BrlR to be an activator of mexAB-oprM and mexEF-oprN gene expression. Moreover, immunoblot analysis confirmed increased MexA abundance in cells overexpressing brlR. Inactivation of both efflux pumps rendered biofilms significantly more susceptible to five different classes of antibiotics by affecting MIC but not the recalcitrance of biofilms to killing by cidal antimicrobial agents. Overexpression of either efflux pump in a ΔbrlR strain partly restored tolerance of ΔbrlR biofilms to antibiotics. Expression of brlR in mutant biofilms lacking both efflux pumps partly restored antimicrobial tolerance of biofilms to wild type levels. Our results indicate that BrlR acts as an activator of multidrug efflux pumps to confer tolerance to P. aeruginosa biofilms and to resist the action of antimicrobial agents.

Phylogenetically diverse species of bacteria can catalyze the oxidation of ferrous iron (Fe(II)) coupled to nitrate (NO3(-)) reduction, often referred to as nitrate-dependent iron oxidation (NDFO). Very little is known about the biochemistry of NDFO, and though growth benefits have been observed, mineral encrustations and nitrite accumulation likely limit growth. Acidovorax ebreus, like other species in the Acidovorax genus, is proficient at catalyzing NDFO. Our results suggest that the induction of specific Fe(II) oxidoreductase proteins is not required for NDFO. No upregulated periplasmic or outer membrane redox active proteins, like those involved in Fe(II) oxidation by acidophilic iron oxidizers or anaerobic photoferrotrophs, were observed in proteomics experiments. We demonstrate that while "abiotic" extracellular reactions between Fe(II) and biogenic NO2(-)/NO can be involved in NDFO, intracellular reactions between Fe(II) and periplasmic components are essential to initiate extensive NDFO. We present evidence that an organic co-substrate inhibits NDFO, likely by keeping periplasmic enzymes in their reduced state or by stimulating metal efflux pumping, or both, and that growth during NDFO relies on the capacity of a nitrate-reducing bacterium to overcome the toxicity of Fe(II) and reactive nitrogen species. Based on our data and evidence in the literature, we postulate that all respiratory nitrate-reducing bacteria are innately capable of catalyzing NDFO. Our findings have implications for a mechanistic understanding of NDFO, the biogeochemical controls on anaerobic Fe(II) oxidation, and the production of NO2(-), NO and N2O in the environment.

Lyme disease is a multi-systemic disorder caused by Borrelia burgdorferi infection. Upon infection, some B. burgdorferi genes are up-regulated, including members of the microbial surface components recognizing adhesive matrix molecule (MSCRAMM) protein family, which facilitate B. burgdorferi adherence to extracellular matrix components of the host. Comparative genome analysis has revealed a new family of B. burgdorferi proteins containing the von Willebrand factor A (vWFA) domain. In the present study, we characterized the expression and membrane association of the vWFA domain-containing protein BB0172, using in vitro transcription/translation systems in the presence of microsomal membranes, and detergent phase separation assays. Our results show evidence of BB0172 localization in the outer membrane, the orientation of the vWFA domain to the extracellular environment, and its function as a metal ion-dependent integrin-binding protein. This is the first report of a borrelial adhesin with a metal ion-dependent adhesion site (MIDAS) motif that is similar to those observed in eukaryotic integrins and has a similar function.

During growth in the environment bacteria encounter stresses which can delay or inhibit their growth. To defend against these stresses bacteria induce both resistance and repair mechanisms. Many bacteria regulate these resistance mechanisms using a group of alternative σ factors called Extra-Cytoplasmic Function (ECF) σ factors. ECF σ factors represent the largest and most diverse family of σ factors. Here we demonstrate that activation of a member of the subfamily of ECF σ factors (ECF30), represented by σ(V) in Bacillus subtilis, is controlled by the proteolytic destruction of the anti-σ factor RsiV. We will demonstrate that degradation of RsiV, and thus activation of σ(V), requires multiple proteolytic steps. Upon exposure to the inducer lysozyme, the extracellular domain of RsiV is removed by an unknown protease, which cleaves at Site-1. This cleavage is independent of PrsW, the B. subtilis Site-1 protease, which cleaves the anti-σ factor RsiW. Following cleavage by the unknown protease the N-term-RsiV requires further processing, which requires the Site-2 intramembrane protease RasP. Our data indicates that N-term-RsiV(1-60) lacking the extracellular domain is constitutively degraded unless RasP is absent, indicating RasP cleavage is constitutive. This suggests the regulatory step in RsiV degradation, and thus σ(V) activation, is controlled at the level of the Site-1 cleavage. Finally, we provide evidence that increased resistance to lysozyme decreases σ(V) activation. Collectively these data provide evidence that the mechanism for σ(V) activation in B. subtilis is controlled by Regulated Intramembrane Proteolysis (RIP) and requires the Site-2 protease RasP.

In the low G+C Gram-positive bacteria, resistance against antimicrobial peptides is often mediated by so-called resistance modules. These consist of a two-component system and an ATP-binding cassette transporter and are characterized by an unusual mode of signal transduction where the transporter acts as sensor of antimicrobial peptides, because the histidine kinase alone cannot detect the substrates directly. Thus the transporters fulfill a dual function as sensors and detoxification systems to confer resistance, but the mechanistic details of these processes are unknown. The paradigm and best-understood example for this is the BceRS-BceAB module of Bacillus subtilis, which mediates resistance against bacitracin, mersacidin and actagardine. Using a random mutagenesis approach, we here show that mutations that affect specific functions of the transporter BceAB are primarily found in the C-terminal region of the permease, BceB, particularly in the eighth transmembrane helix. Further, we show that while signalling and resistance are functionally interconnected, several mutations could be identified that strongly affected one activity of the transporter, but only had minor effects on the other. Thus a partial genetic separation of the two properties could be achieved by single amino-acid replacements, providing first insights into the signalling mechanism of these unusual modules.

Pseudomonas aeruginosa PAO1 has two differentially expressed methionine sulfoxide reductase genes: msrA (PA5018) and msrB (PA2827). The msrA gene is expressed constitutively at a high level throughout all growth phases, whereas msrB expression is highly induced by oxidative stress, such as sodium hypochlorite (NaOCl) treatment. Inactivation of either msrA or msrB or both genes (msrA-msrB) rendered the mutants less resistant than the parental PAO1 strain to oxidants such as NaOCl and H2O2. Unexpectedly, msr mutants have disparate resistance patterns when exposed to paraquat, a superoxide generator. The msrA mutant had a higher paraquat resistance level than the msrB mutant, which had a lower paraquat resistance level than the PAO1 strain. The expression levels of msrA showed an inverse correlation with the paraquat resistance level, and this atypical paraquat resistance pattern was not observed with msrB. Virulence testing using a Drosophila melanogaster model revealed that msrA, msrB and, to a greater extent, double msrA-msrB mutants had an attenuated virulence phenotype. The data indicate that msrA and msrB are essential genes for oxidative stress protection and bacterial virulence. The pattern of expression and mutant phenotypes of P. aeruginosa msrA and msrB differ from previously characterized msr genes from other bacteria. Thus, as highly conserved genes, the msrA and msrB have diverse expression patterns and physiological roles that depend on the environmental niche where the bacteria thrive.

During the transition from a free-swimming, single-cell life-style to a sessile, multicellular state called a biofilm, bacteria produce and secrete an extracellular matrix comprised of nucleic acids, exopolysaccharides and adhesion proteins. The Vibrio cholerae biofilm matrix contains three major protein components, RbmA, Bap1 and RbmC, which are unique to Vibrio cholerae and appear to support biofilm formation at particular steps in the process. Here, we focus on RbmA, a structural protein with an unknown fold. RbmA participates in the early cell-cell adhesion events, and is found throughout the biofilm where it localizes to cell-cell contact sites. We determined crystal structures of RbmA and revealed that the protein folds into tandem fibronectin III (FnIII) folds. The protein is dimeric in solution and in crystals, with the dimer interface displaying a surface groove that is lined with several positively charged residues. Structure-guided mutagenesis studies establish a crucial role for this surface patch for RbmA function. Based on the structure, we hypothesize that RbmA serves as a tether by maintaining flexible linkages between cells and the extracellular matrix.

The intracellular bacterial agent of Q fever, Coxiella burnetii, translocates effector proteins into its host cell cytosol via a Dot/Icm type IV secretion system (T4SS). The T4SS is essential for parasitophorous vacuole formation, intracellular replication, and inhibition of host cell death, but effectors mediating these events remain largely undefined. Six Dot/Icm substrate-encoding genes were recently discovered on the C. burnetii cryptic QpH1 plasmid, three of which are conserved among all C. burnetii isolates, suggesting they are critical for conserved pathogen functions. However, remaining hypothetical proteins encoded by plasmid genes have not been assessed for their potential as T4SS substrates. In the current study, we further defined the T4SS effector repertoire encoded by the C. burnetii QpH1, QpRS, and QpDG plasmids that were originally isolated from acute disease, chronic disease, and severely attenuated isolates, respectively. Hypothetical proteins, including those specific to QpRS or QpDG, were screened for translocation using the well-established Legionella pneumophila T4SS secretion model. In total, six novel plasmid-encoded proteins were translocated into macrophage-like cells by the Dot/Icm T4SS. Four newly identified effectors are encoded by genes only present on the QpDG plasmid from severely attenuated Dugway isolates, suggesting presence of specific effectors correlates with decreased virulence. These results further support a critical role for extrachromosomal elements in C. burnetii pathogenesis.