Differential regulation of the Proteus mirabilis urease gene cluster by UreR and H-NS

Proteus mirabilis UreR coordinates cellular functions required for urease activity

A hallmark of Proteus mirabilis infection of the urinary tract is the formation of stones. The ability to induce urinary stone formation requires urease, a nickel metalloenzyme that hydrolyzes urea. This reaction produces ammonia as a byproduct, which can serve as a nitrogen source and weak base that raises the local pH. The resulting alkalinity induces the precipitation of ions to form stones. Transcriptional regulator UreR activates expression of urease genes in a urea-dependent manner. Thus, urease genes are highly expressed in the urinary tract where urea is abundant. Production of mature urease also requires the import of nickel into the cytoplasm and its incorporation into the urease apoenzyme. Urease accessory proteins primarily acquire nickel from one of two nickel transporters and facilitate incorporation of nickel to form mature urease. In this study, we performed a comprehensive RNA-seq to define the P. mirabilis urea-induced transcriptome as well as the UreR regulon. We identified UreR as the first defined regulator of nickel transport in P. mirabilis. We also offer evidence for the direct regulation of the Ynt nickel transporter by UreR. Using bioinformatics, we identified UreR-regulated urease loci in 15 Morganellaceae family species across three genera. Additionally, we located two mobilized UreR-regulated urease loci that also encode the ynt transporter, implying that UreR regulation of nickel transport is a conserved regulatory relationship. Our study demonstrates that UreR specifically regulates genes required to produce mature urease, an essential virulence factor for P. mirabilis uropathogenesis.

IMPORTANCE

Catheter-associated urinary tract infections (CAUTIs) account for over 40% of acute nosocomial infections in the USA and generate $340 million in healthcare costs annually. A major causative agent of CAUTIs is Proteus mirabilis, an understudied Gram-negative pathogen noted for its ability to form urinary stones via the activity of urease. Urease mutants cannot induce stones and are attenuated in a murine UTI model, indicating this enzyme is essential to P. mirabilis pathogenesis. Transcriptional regulation of urease genes by UreR is well established; here, we expand the UreR regulon to include regulation of nickel import, a function required to produce mature urease. Furthermore, we reflect on the role of urea catalysis in P. mirabilis metabolism and provide evidence for its importance.

Features of Hemolysin Biosynthesis by Morganella morganii

We studied the influence of medium composition and aeration on the hemolytic activity of uropathogenic Morganella morganii strain MM 190. The maximum level of hemolysis was observed in LB (59%), DMEM supplemented with fetal bovine serum (62%), and urine (53%) under aeration conditions during the exponential growth phase. The presence of 2% urea in the medium suppressed hemolysin synthesis. Moreover, addition of bacterial culture fluid containing hemolysin to a monolayer of T-24 bladder carcinoma and OKP-GS kidney carcinoma cells led to 25 and 42% cell death, respectively. We found that the maximum expression of the hemolysin gene hlyA was observed in 2-h culture in LB medium, which correlated with the hemolytic activity of the bacteria in this medium and indicated the predominance of the short hlyCA transcript in the cells.

N-acetylcysteine prevents catheter occlusion and inflammation in catheter associated-urinary tract infections by suppressing urease activity

Introduction

Proteus mirabilis is a key pathobiont in catheter-associated urinary tract infections (CA-UTIs), which is well known to form crystalline biofilms that occlude catheters. Urease activity alkylates urine through the release of ammonia, consequentially resulting in higher levels of Mg2+ and Ca2+ and formation of crystals. In this study, we showed that N-acetyl cysteine (NAC), a thiol antioxidant, is a potent urease inhibitor that prevents crystalline biofilm formation.

Methods

To quantify urease activity, Berthelot's method was done on bacterial extracts treated with NAC. We also used an in vitro catheterised glass bladder model to study the effect of NAC treatment on catheter occlusion and biofilm encrustation in P. mirabilis infections. Inductively-coupled plasma mass spectrometry (ICP-MS) was performed on catheter samples to decipher elemental profiles.

Results

NAC inhibits urease activity of clinical P. mirabilis isolates at concentrations as low as 1 mM, independent of bacterial killing. The study also showed that NAC is bacteriostatic on P. mirabilis, and inhibited biofilm formation and catheter occlusion in an in vitro. A significant 4-8log10 reduction in viable bacteria was observed in catheters infected in this model. Additionally, biofilms in NAC treated catheters displayed a depletion of calcium, magnesium, or phosphates (>10 fold reduction), thus confirming the absence of any urease activity in the presence of NAC. Interestingly, we also showed that not only is NAC anti-inflammatory in bladder epithelial cells (BECs), but that it mutes its inflammatory response to urease and P. mirabilis infection by reducing the production of IL-6, IL-8 and IL-1b.

Discussion

Using biochemical, microbiological and immunological techniques, this study displays the functionality of NAC in preventing catheter occlusion by inhibiting urease activity. The study also highlights NAC as a strong anti-inflammatory antibiofilm agent that can target both bacterial and host factors in the treatment of CA-UTIs.

New vectors for urea-inducible recombinant protein production

We have developed a novel urea-inducible recombinant protein production system by exploiting the Proteus mirabilis urease ureR-ureD promoter region and the ureR AraC-family transcriptional regulator. Experiments using the expression of β-galactosidase and green fluorescent protein (GFP) showed that promoter activity is tightly regulated and that varying the concentration of urea can give up to 100-fold induction. Production of proteins of biopharmaceutical interest has been demonstrated, including human growth hormone (hGH), a single chain antibody fragment (scFv) against interleukin-1β and a potential Neisserial vaccine candidate (BamA_ENm). Expression levels can be fine-tuned by temperature and different urea concentrations, and can be induced with readily available garden fertilisers and even urine. As urea is an inexpensive, stable inducer, a urea-induced expression system has the potential to considerably reduce the costs of large-scale recombinant protein production.

Breast milk urea as a nitrogen source for urease positive Bifidobacterium infantis

Human milk stimulates a health-promoting gut microbiome in infants. However, it is unclear how the microbiota salvages and processes its required nitrogen from breast milk. Human milk nitrogen sources such as urea could contribute to the composition of this early life microbiome. Urea is abundant in human milk, representing a large part of the non-protein nitrogen (NPN). We found that B. longum subsp. infantis (ATCC17930) can use urea as a main source of nitrogen for growth in synthetic medium and enzyme activity was induced by the presence of urea in the medium. We furthermore confirmed the expression of both urease protein subunits and accessory proteins of B. longum subsp. infantis through proteomics. To the same end, metagenome data were mined for urease-related genes. It was found that the breastfed infant's microbiome possessed more urease-related genes than formula fed infants (51.4:22.1; 2.3-fold increase). Bifidobacteria provided a total of 106 of urease subunit alpha alignments, found only in breastfed infants. These experiments show how an important gut commensal that colonizes the infant intestine can metabolize urea. The results presented herein further indicate how dietary nitrogen can determine bacterial metabolism in the neonate gut and shape the overall microbiome.

Proteomic analysis deciphers the multi-targeting antivirulence activity of tannic acid in modulating the expression of MrpA, FlhD, UreR, HpmA and Nrp system in Proteus mirabilis

In the present study, the multi-targeting antivirulence activity of tannic acid (TA) was explored against Proteus mirabilis through MS-based proteomic approach. The in vitro biofilm biomass quantification assay and microscopic analysis demonstrated the antibiofilm activity of TA against P. mirabilis in which, minimum biofilm inhibitory concentration (MBIC) of TA was found to be 200 μg/mL concentration. Moreover, the nanoscale liquid chromatography coupled to tandem mass spectrometry (nano LC-MS/MS) analysis revealed that TA (at MBIC) differentially regulated the proteins involved in fimbrial adhesion, flagellar motility, iron acquisition, Fe-S cluster assembly, heat shock response, virulence enzymes, and toxin secretion. Further, the transcriptomic analysis validated the outcomes of proteomic analysis in which, the expression level of virulence genes responsible for MR/P fimbrial adhesion (mrpA), flagellar transcriptional activation (flhD), biosynthesis of urease (ureR), hemolysin (hpmA), non-ribosomal peptide siderophore system (Nrp), oxidative stress responsible enzymes and fitness factors proteins were down-regulated in TA exposed P. mirabilis. These observations were also in correspondence with the in vitro bioassays. Thus, this study reports the feasibility of TA to act as a promising therapeutic agent against multifactorial P. mirabilis infections.

Urease Expression in Pathogenic Yersinia enterocolitica Strains of Bio-Serotypes 2/O:9 and 1B/O:8 Is Differentially Regulated by the OmpR Regulator

Yersinia enterocolitica exhibits a dual lifestyle, existing as both a saprophyte and a pathogen colonizing different niches within a host organism. OmpR has been recognized as a regulator that controls the expression of genes involved in many different cellular processes and the virulence of pathogenic bacteria. Here, we have examined the influence of OmpR and varying temperature (26°C vs. 37°C) on the cytoplasmic proteome of Y. enterocolitica Ye9N (bio-serotype 2/O:9, low pathogenicity). Differential label-free quantitative proteomic analysis indicated that OmpR affects the cellular abundance of a number of proteins including subunits of urease, an enzyme that plays a significant role in acid tolerance and the pathogenicity of Y. enterocolitica. The impact of OmpR on the expression of urease under different growth conditions was studied in more detail by comparing urease activity and the transcription of ure genes in Y. enterocolitica strains Ye9N and Ye8N (highly pathogenic bio-serotype 1B/O:8). Urease expression was higher in strain Ye9N than in Ye8N and in cells grown at 26°C compared to 37°C. However, low pH, high osmolarity and the presence of urea did not have a clear effect on urease expression in either strain. Further analysis showed that OmpR participates in the positive regulation of three transcriptional units encoding the multi-subunit urease (ureABC, ureEF, and ureGD) in strain Ye9N, but this was not the case in strain Ye8N. Binding of OmpR to the ureABC and ureEF promoter regions was confirmed using an electrophoretic mobility shift assay, suggesting that this factor plays a direct role in regulating the transcription of these operons. In addition, we determined that OmpR modulates the expression of a ureR-like gene encoding a putative regulator of the ure gene cluster, but in the opposite manner, i.e., positively in Ye9N and negatively in Ye8N. These findings provide some novel insights into the function of OmpR in adaptation strategies of Y. enterocolitica.

Pathogenesis of Proteus mirabilis Infection

Proteus mirabilis, a Gram-negative rod-shaped bacterium most noted for its swarming motility and urease activity, frequently causes catheter-associated urinary tract infections (CAUTIs) that are often polymicrobial. These infections may be accompanied by urolithiasis, the development of bladder or kidney stones due to alkalinization of urine from urease-catalyzed urea hydrolysis. Adherence of the bacterium to epithelial and catheter surfaces is mediated by 17 different fimbriae, most notably MR/P fimbriae. Repressors of motility are often encoded by these fimbrial operons. Motility is mediated by flagella encoded on a single contiguous 54-kb chromosomal sequence. On agar plates, P. mirabilis undergoes a morphological conversion to a filamentous swarmer cell expressing hundreds of flagella. When swarms from different strains meet, a line of demarcation, a "Dienes line," develops due to the killing action of each strain's type VI secretion system. During infection, histological damage is caused by cytotoxins including hemolysin and a variety of proteases, some autotransported. The pathogenesis of infection, including assessment of individual genes or global screens for virulence or fitness factors has been assessed in murine models of ascending urinary tract infections or CAUTIs using both single-species and polymicrobial models. Global gene expression studies performed in culture and in the murine model have revealed the unique metabolism of this bacterium. Vaccines, using MR/P fimbria and its adhesin, MrpH, have been shown to be efficacious in the murine model. A comprehensive review of factors associated with urinary tract infection is presented, encompassing both historical perspectives and current advances.

Emerging medical and engineering strategies for the prevention of long-term indwelling catheter blockage

Urinary catheters have been used on an intermittent or indwelling basis for centuries, in order to relieve urinary retention and incontinence. Nevertheless, the use of urinary catheters in the clinical setting is fraught with complication, the most common of which is the development of nosocomial urinary tract infections, known as catheter-associated urinary tract infections. Infections of this nature are not only significant owing to their high incidence rate and subsequent economic burden but also to the severe medical consecutions that result. A range of techniques have been employed in recent years, utilising various technologies in attempts to counteract the perilous medical cascade following catheter blockage. This review will focus on the current advancement (within the last 10 years) in prevention of encrustation and blockage of long-term indwelling catheters both from engineering and medical perspectives, with particular emphasis on the importance of stimuli-responsive systems.

Determinants of the regulation of Helicobacter pylori adhesins include repeat sequences in both promoter and coding regions as well as the two-component system ArsRS

PURPOSE

We investigated the transcription of adhesin-encoding genes sabA, hopZ and labA in Helicobacter pylori strain J99. Each possesses a repeating homopolymeric nucleotide tract within their promoter regions, and sabA and hopZ possess repeats within their 5' coding regions.

METHODOLOGY

We altered the repeat lengths associated with the adhesin genes and quantified mRNA levels by real-time quantitative PCR. Using adherence to AGS cells and IL-8 assays, we examined the effects of altered transcript levels. We assessed the role of ArsRS in transcription using an arsS null mutant and by examining ArsR binding to promoter regions via electrophoretic mobility shift assays.

RESULTS

Extensions or truncations of promoter region repeats in hopZ and labA increased transcript levels, mirroring results shown by our lab and others for mutations in the sabA promoter. Altered lengths of the poly-cytosine thymine tract within the 5' coding region of sabA demonstrated that switching from phase-off to phase-on significantly increased mRNA levels. However, mutations in the poly-thymine tract of sabA, which increased mRNA levels, do not behave synergistically with phase-on mutations. Phase-on mutations of sabA resulted in increased H. pylori adherence to AGS cells, but only a modest effect on IL-8. hopZ and labA, and sabA paralogue sabB, transcript levels were increased in an arsS mutant and ArsR bound the promoter regions for each of these genes in vitro.

CONCLUSION

This work highlights the complex nature of adhesin regulation, its impact on H. pylori attachment and the pervasive role of ArsRS in adhesin expression. Such regulation may help facilitate the decades-long persistence of infection.

Role of the Histone-Like Nucleoid Structuring Protein (H-NS) in the Regulation of Virulence Factor Expression and Stress Response in Vibrio vulnificus

Temperature is one of the important parameters regulating the expression of virulence factors in bacteria. The global regulator, a histone-like nucleoid structuring protein (H-NS), is known to play a crucial role in this regulation. In the present study, we first clarified the role of H-NS in the temperature-dependent regulation of virulence factor production in Vibrio vulnificus, including that of the cytolytic toxin (V. vulnificus hemolysin: VVH) and the proteolytic enzyme (V. vulnificus protease: VVP). The expression of hns itself was subjected to temperature regulation, where hns was expressed more at 26 ℃ than at 37 ℃. VVH production and the expression of its gene vvhA were increased by disruption of the hns gene. H-NS appeared to affect the vvhA expression by the well-documented transcriptional silencing mechanism. On the other hand, hns disruption resulted in the reduction of VVP production and the expression of its gene vvpE. H-NS was suggested to positively regulate vvpE expression through the increase in the level of the rpoS mRNA. Moreover, H-NS was found to contribute to the survival of V. vulnificus in stressful environments. When compared to the wild type strain, the hns mutant exhibited reduced survival rates when subjected to acidic pH, hyperosmotic and oxidative stress.

Proteus mirabilis and Urinary Tract Infections

Proteus mirabilis is a Gram-negative bacterium and is well known for its ability to robustly swarm across surfaces in a striking bulls'-eye pattern. Clinically, this organism is most frequently a pathogen of the urinary tract, particularly in patients undergoing long-term catheterization. This review covers P. mirabilis with a focus on urinary tract infections (UTI), including disease models, vaccine development efforts, and clinical perspectives. Flagella-mediated motility, both swimming and swarming, is a central facet of this organism. The regulation of this complex process and its contribution to virulence is discussed, along with the type VI-secretion system-dependent intra-strain competition, which occurs during swarming. P. mirabilis uses a diverse set of virulence factors to access and colonize the host urinary tract, including urease and stone formation, fimbriae and other adhesins, iron and zinc acquisition, proteases and toxins, biofilm formation, and regulation of pathogenesis. While significant advances in this field have been made, challenges remain to combatting complicated UTI and deciphering P. mirabilis pathogenesis.

Virulence Gene Regulation in Escherichia coli

Escherichia colicauses three types of illnesses in humans: diarrhea, urinary tract infections, and meningitis in newborns. The acquisition of virulence-associated genes and the ability to properly regulate these, often horizontally transferred, loci distinguishes pathogens from the normally harmless commensal E. coli found within the human intestine. This review addresses our current understanding of virulence gene regulation in several important diarrhea-causing pathotypes, including enteropathogenic, enterohemorrhagic,enterotoxigenic, and enteroaggregativeE. coli-EPEC, EHEC, ETEC and EAEC, respectively. The intensely studied regulatory circuitry controlling virulence of uropathogenicE. coli, or UPEC, is also reviewed, as is that of MNEC, a common cause of meningitis in neonates. Specific topics covered include the regulation of initial attachment events necessary for infection, environmental cues affecting virulence gene expression, control of attaching and effacing lesionformation, and control of effector molecule expression and secretion via the type III secretion systems by EPEC and EHEC. How phage control virulence and the expression of the Stx toxins of EHEC, phase variation, quorum sensing, and posttranscriptional regulation of virulence determinants are also addressed. A number of important virulence regulators are described, including the AraC-like molecules PerA of EPEC, CfaR and Rns of ETEC, and AggR of EAEC;the Ler protein of EPEC and EHEC;RfaH of UPEC;and the H-NS molecule that acts to silence gene expression. The regulatory circuitry controlling virulence of these greatly varied E. colipathotypes is complex, but common themes offerinsight into the signals and regulators necessary forE. coli disease progression.

Evolutionary adaptation of an AraC-like regulatory protein in Citrobacter rodentium and Escherichia species

The evolution of pathogenic bacteria is a multifaceted and complex process, which is strongly influenced by the horizontal acquisition of genetic elements and their subsequent expression in their new hosts. A well-studied example is the RegA regulon of the enteric pathogen Citrobacter rodentium. The RegA regulatory protein is a member of the AraC/XylS superfamily, which coordinates the expression of a gene repertoire that is necessary for full pathogenicity of this murine pathogen. Upon stimulation by an exogenous, gut-associated signal, namely, bicarbonate ions, RegA activates the expression of a series of genes, including virulence factors, such as autotransporters, fimbriae, a dispersin-like protein, and the grlRA operon on the locus of enterocyte effacement pathogenicity island. Interestingly, the genes encoding RegA homologues are distributed across the genus Escherichia, encompassing pathogenic and nonpathogenic subtypes. In this study, we carried out a series of bioinformatic, transcriptional, and functional analyses of the RegA regulons of these bacteria. Our results demonstrated that regA has been horizontally transferred to Escherichia spp. and C. rodentium. Comparative studies of two RegA homologues, namely, those from C. rodentium and E. coli SMS-3-5, a multiresistant environmental strain of E. coli, showed that the two regulators acted similarly in vitro but differed in terms of their abilities to activate the virulence of C. rodentium in vivo, which evidently was due to their differential activation of grlRA. Our data indicate that RegA from C. rodentium has strain-specific adaptations that facilitate infection of its murine host. These findings shed new light on the development of virulence by C. rodentium and on the evolution of virulence-regulatory genes of bacterial pathogens in general.

Repetitive sequence variations in the promoter region of the adhesin-encoding gene sabA of Helicobacter pylori affect transcription

The pathogenesis of diseases elicited by the gastric pathogen Helicobacter pylori is partially determined by the effectiveness of adaptation to the variably acidic environment of the host stomach. Adaptation includes appropriate adherence to the gastric epithelium via outer membrane protein adhesins such as SabA. The expression of sabA is subject to regulation via phase variation in the promoter and coding regions as well as repression by the two-component system ArsRS. In this study, we investigated the role of a homopolymeric thymine [poly(T)] tract -50 to -33 relative to the sabA transcriptional start site in H. pylori strain J99. We quantified sabA expression in H. pylori J99 by quantitative reverse transcription-PCR (RT-PCR), demonstrating significant changes in sabA expression associated with experimental manipulations of poly(T) tract length. Mimicking the length increase of this tract by adding adenines instead of thymines had similar effects, while the addition of other nucleotides failed to affect sabA expression in the same manner. We hypothesize that modification of the poly(T) tract changes DNA topology, affecting regulatory protein interaction(s) or RNA polymerase binding efficiency. Additionally, we characterized the interaction between the sabA promoter region and ArsR, a response regulator affecting sabA expression. Using recombinant ArsR in electrophoretic mobility shift assays (EMSA), we localized binding to a sequence with partial dyad symmetry -20 and +38 relative to the sabA +1 site. The control of sabA expression by both ArsRS and phase variation at two distinct repeat regions suggests the control of sabA expression is both complex and vital to H. pylori infection.

Merging mythology and morphology: the multifaceted lifestyle of Proteus mirabilis

Proteus mirabilis, named for the Greek god who changed shape to avoid capture, has fascinated microbiologists for more than a century with its unique swarming differentiation, Dienes line formation and potent urease activity. Transcriptome profiling during both host infection and swarming motility, coupled with the availability of the complete genome sequence for P. mirabilis, has revealed the occurrence of interbacterial competition and killing through a type VI secretion system, and the reciprocal regulation of adhesion and motility, as well as the intimate connections between metabolism, swarming and virulence. This Review addresses some of the unique and recently described aspects of P. mirabilis biology and pathogenesis, and emphasizes the potential role of this bacterium in single-species and polymicrobial urinary tract infections.

Induction of the ferritin gene (ftnA) of Escherichia coli by Fe(2+)-Fur is mediated by reversal of H-NS silencing and is RyhB independent

FtnA is the major iron-storage protein of Escherichia coli accounting for < or = 50% of total cellular iron. The FtnA gene (ftnA) is induced by iron in an Fe(2+)-Fur-dependent fashion. This effect is reportedly mediated by RyhB, the Fe(2+)-Fur-repressed, small, regulatory RNA. However, results presented here show that ftnA iron induction is independent of RyhB and instead involves direct interaction of Fe(2+)-Fur with an 'extended' Fur binding site (containing five tandem Fur boxes) located upstream (-83) of the ftnA promoter. In addition, H-NS acts as a direct repressor of ftnA transcription by binding at multiple sites (I-VI) within, and upstream of, the ftnA promoter. Fur directly competes with H-NS binding at upstream sites (II-IV) and consequently displaces H-NS from the ftnA promoter (sites V-VI) which in turn leads to derepression of ftnA transcription. It is proposed that H-NS binding within the ftnA promoter is facilitated by H-NS occupation of the upstream sites through H-NS oligomerization-induced DNA looping. Consequently, Fur displacement of H-NS from the upstream sites prevents cooperative H-NS binding at the downstream sites within the promoter, thus allowing access to RNA polymerase. This direct activation of ftnA transcription by Fe(2+)-Fur through H-NS antisilencing represents a new mechanism for iron-induced gene expression.

The DNA static curvature has a role in the regulation of the ompS1 porin gene in Salmonella enterica serovar Typhi

The DNA static curvature has been described to play a key role as a regulatory element in the transcription process of several bacterial genes. Here, the role of DNA curvature in the expression of the ompS1 porin gene in Salmonella enterica serovar Typhi is described. The web server mutacurve was used to predict mutations that diminished or restored the extent of DNA curvature in the 5' regulatory region of ompS1. Using these predictions, curvature was diminished by site-directed mutagenesis of only two residues, and curvature was restored by further mutagenesis of the same two residues. Lowering the extent of DNA curvature resulted in an increase in ompS1 expression and in the diminution of the affinity of the silencer proteins H-NS and StpA for the ompS1 5' regulatory region. These mutations were in a region shown not to contain the H-NS nucleation site, consistent with the notion that the effect on expression was due to changes in DNA structural topology.

HlyU acts as an H-NS antirepressor in the regulation of the RTX toxin gene essential for the virulence of the human pathogen Vibrio vulnificus CMCP6

In Vibrio vulnificus, HlyU upregulates the expression of the large RTX toxin gene. In this work we identified the binding site of HlyU to -417 to -376 bp of the rtxA1 operon transcription start site. lacZ fusions for a series of progressive deletions from the rtxA1 operon promoter showed that transcriptional activity increased independently of HlyU when its binding site was absent. Thus HlyU must regulate the rtxA1 operon expression by antagonizing a negative regulator. Concomitantly we found that an hns mutant resulted in an increase in the expression of the rtxA1 operon genes. Multiple copies of HlyU can increase the promoter activity only in the presence of H-NS underscoring the hypothesis that HlyU must alleviate the repression by this protein. H-NS binds to a region that extends upstream and downstream of the rtxA1 operon promoter. In the upstream region it binds to five AT-rich sites of which two overlap the HlyU binding site. Competitive footprinting and gel shift data demonstrate HlyU's higher affinity as compared with H-NS resulting in the de-repression and a corresponding increased expression of the rtxA1 operon.

Complicated catheter-associated urinary tract infections due to Escherichia coli and Proteus mirabilis

Catheter-associated urinary tract infections (CAUTIs) represent the most common type of nosocomial infection and are a major health concern due to the complications and frequent recurrence. These infections are often caused by Escherichia coli and Proteus mirabilis. Gram-negative bacterial species that cause CAUTIs express a number of virulence factors associated with adhesion, motility, biofilm formation, immunoavoidance, and nutrient acquisition as well as factors that cause damage to the host. These infections can be reduced by limiting catheter usage and ensuring that health care professionals correctly use closed-system Foley catheters. A number of novel approaches such as condom and suprapubic catheters, intermittent catheterization, new surfaces, catheters with antimicrobial agents, and probiotics have thus far met with limited success. While the diagnosis of symptomatic versus asymptomatic CAUTIs may be a contentious issue, it is generally agreed that once a catheterized patient is believed to have a symptomatic urinary tract infection, the catheter is removed if possible due to the high rate of relapse. Research focusing on the pathogenesis of CAUTIs will lead to a better understanding of the disease process and will subsequently lead to the development of new diagnosis, prevention, and treatment options.

Transcriptional organization of the temperature-sensitive transfer system from the IncHI1 plasmid R27

One of the characteristic features of IncHI1 plasmids is a thermosensitive process of conjugation, which is optimal between 22 °C and 30 °C but inhibited at 37 °C. R27, the prototypical IncHI1 plasmid, contains transfer genes clustered in two regions of the plasmid, Tra1 and Tra2. In the present study, transcriptional analyses of thetragenes were undertaken at both 30 °C and 37 °C. Screening of 38tragenes showed thattragenes are transcriptionally linked in six operons, three in each Tra region. RT-PCR analysis showed that gene expression was reduced at 37 °C relative to that observed at 30 °C. The transcription start sites of the six transcripts were identified, promoters and upstream regions were cloned, and transcription was tested at both temperatures. In cells grown at 37 °C, in the presence of R27, the promoters were inhibited, except for promoters of the H operon and AN operon. Conditions that influenced DNA topology, such as osmolarity, anaerobiosis, quorum sensing and acidity, showed no significant influence on transfer frequency. These results should facilitate future understanding of the basis of temperature-sensitive transfer in this large conjugative plasmid.

SspA is required for acid resistance in stationary phase by downregulation of H-NS inEscherichia coli

The stringent starvation protein A (SspA) is a RNA polymerase-associated protein and is required for transcriptional activation of bacteriophage P1 late promoters. However, the role of SspA in gene expression in Escherichia coli is essentially unknown. In this work, we show that SspA is essential for cell survival during acid-induced stress. Apparently, SspA inhibits stationary-phase accumulation of H-NS, a global regulator which functions mostly as a repressor, thereby derepressing multiple stress defence systems including those for acid stress and nutrient starvation. Consequently, the gene expression pattern of the H-NS regulon is altered in the sspA mutant, leading to acid-sensitive and hypermotile phenotypes. Thus, our study indicates that SspA is a global regulator, which acts upstream of H-NS, and thereby plays an important role in the stress response of E. coli during stationary phase. In addition, our results indicate that the expression of the H-NS regulon is sensitive to small changes in the cellular level of H-NS, enabling the cell to response rapidly to environment cues. As SspA and H-NS are highly conserved among Gram-negative bacteria, of which many are pathogenic, the global role of SspA in the stress response and pathogenesis is discussed.

Molecular identification of the urea uptake system and transcriptional analysis of urea transporter- and urease-encoding genes in Corynebacterium glutamicum

The molecular identification of the Corynebacterium glutamicum urea uptake system is described. This ABC-type transporter is encoded by the urtABCDE operon, which is transcribed in response to nitrogen limitation. Expression of the urt genes is regulated by the global nitrogen regulator AmtR, and an amtR deletion strain showed constitutive expression of the urtABCDE genes. The AmtR repressor protein also controls transcription of the urease-encoding ureABCEFGD genes in C. glutamicum. The ure gene cluster forms an operon which is mainly transcribed in response to nitrogen starvation. To confirm the increased synthesis of urease subunits under nitrogen limitation, proteome analyses of cytoplasmic protein extracts from cells grown under nitrogen surplus and nitrogen limitation were carried out, and five of the seven urease subunits were identified.