Transcriptional and translational expression patterns associated with immobilized growth of Campylobacter jejuni

Antimicrobial Resistance Gene Transfer from Campylobacter jejuni in Mono- and Dual-Species Biofilms

Horizontal gene transfer (HGT) is a driving force for the dissemination of antimicrobial resistance (AMR) genes among Campylobacter jejuni organisms, a leading cause of foodborne gastroenteritis worldwide. Although HGT is well documented for C. jejuni planktonic cells, the role of C. jejuni biofilms in AMR spread that likely occurs in the environment is poorly understood. Here, we developed a cocultivation model to investigate the HGT of chromosomally encoded AMR genes between two C. jejuni F38011 AMR mutants in biofilms. Compared to planktonic cells, C. jejuni biofilms significantly promoted HGT (P < 0.05), resulting in an increase of HGT frequencies by up to 17.5-fold. Dynamic study revealed that HGT in biofilms increased at the early stage (i.e., from 24 h to 48 h) and remained stable during 48 to 72 h. Biofilms continuously released the HGT mutants into supernatant culture, indicating spontaneous dissemination of AMR to broader niches. DNase I treatment confirmed the role of natural transformation in genetic exchange. HGT was not associated with biofilm biomass, cell density, or bacterial metabolic activity, whereas the presence of extracellular DNA was negatively correlated with the altered HGT frequencies. HGT in biofilms also had a strain-to-strain variation. A synergistic HGT effect was observed between C. jejuni with different genomic backgrounds (i.e., C. jejuni NCTC 11168 chloramphenicol-resistant strain and F38011 kanamycin-resistant strain). C. jejuni performed HGT at the frequency of 10-7 in Escherichia coli-C. jejuni biofilms, while HGT was not detectable in Salmonella enterica-C. jejuni biofilms. IMPORTANCE Antimicrobial-resistant C. jejuni has been listed as a high priority of public health concern worldwide. To tackle the rapid evolution of AMR in C. jejuni, it is of great importance to understand the extent and characteristics of HGT in C. jejuni biofilms, which serve as the main survival strategy of this microbe in the farm-to-table continuum. In this study, we demonstrated that biofilms significantly enhanced HGT compared to the planktonic state (P < 0.05). Biofilm cultivation time and extracellular DNA (eDNA) amount were related to varied HGT frequencies. C. jejuni could spread AMR genes in both monospecies and dual-species biofilms, mimicking the survival mode of C. jejuni in food chains. These findings indicated that the risk and extent of AMR transmission among C. jejuni organisms have been underestimated, as previous HGT studies mainly focused on the planktonic state. Future AMR controlling measures can target biofilms and their main component eDNA.

Static Growth Promotes PrrF and 2-Alkyl-4(1H)-Quinolone Regulation of Type VI Secretion Protein Expression in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that is frequently associated with both acute and chronic infections. P. aeruginosa possesses a complex regulatory network that modulates nutrient acquisition and virulence, but our knowledge of these networks is largely based on studies with shaking cultures, which are not likely representative of conditions during infection. Here, we provide proteomic, metabolic, and genetic evidence that regulation by iron, a critical metallonutrient, is altered in static P. aeruginosa cultures. Specifically, we observed a loss of iron-induced expression of proteins for oxidative phosphorylation, tricarboxylic acid (TCA) cycle metabolism under static conditions. Moreover, we identified type VI secretion as a target of iron regulation in P. aeruginosa cells under static but not shaking conditions, and we present evidence that this regulation occurs via PrrF small regulatory RNA (sRNA)-dependent production of 2-alkyl-4(1H)-quinolone metabolites. These results yield new iron regulation paradigms in an important opportunistic pathogen and highlight the need to redefine iron homeostasis in static microbial communities.IMPORTANCE Host-mediated iron starvation is a broadly conserved signal for microbial pathogens to upregulate expression of virulence traits required for successful infection. Historically, global iron regulatory studies in microorganisms have been conducted in shaking cultures to ensure culture homogeneity, yet these conditions are likely not reflective of growth during infection. Pseudomonas aeruginosa is a well-studied opportunistic pathogen and model organism for iron regulatory studies. Iron homeostasis is maintained through the Fur protein and PrrF small regulatory sRNAs, the functions of which are highly conserved in many other bacterial species. In the current study, we examined how static growth affects the known iron and PrrF regulons of P. aeruginosa, leading to the discovery of novel PrrF-regulated virulence processes. This study demonstrates how the utilization of distinct growth models can enhance our understanding of basic physiological processes that may also affect pathogenesis.

Persistent contamination of raw milk by Campylobacter jejuni ST-883

Campylobacter jejuni has caused several campylobacteriosis outbreaks via raw milk consumption. This study reports follow-up of a milk-borne campylobacteriosis outbreak that revealed persistent C. jejuni contamination of bulk tank milk for seven months or longer. Only the outbreak-causing strain, representing sequence type (ST) 883, was isolated from milk, although other C. jejuni STs were also isolated from the farm. We hypothesized that the outbreak strain harbors features that aid its environmental transmission or survival in milk. To identify such phenotypic features, the outbreak strain was characterized for survival in refrigerated raw milk and in aerobic broth culture by plate counting and for biofilm formation on microplates by crystal violet staining and quantification. Furthermore, whole-genome sequences were studied for such genotypic features. For comparison, we characterized isolates representing other STs from the same farm and an ST-883 isolate that persisted on another dairy farm, but was not isolated from bulk tank milk. With high inocula (105 CFU/ml), ST-883 strains survived in refrigerated raw milk longer (4-6 days) than the other strains (≤3 days), but the outbreak strain showed no outperformance among ST-883 strains. This suggests that ST-883 strains may share features that aid their survival in milk, but other mechanisms are required for persistence in milk. No correlation was observed between survival in refrigerated milk and aerotolerance. The outbreak strain formed a biofilm, offering a potential explanation for persistence in milk. Whether biofilm formation was affected by pTet-like genomic element and phase-variable genes encoding capsular methyltransferase and cytochrome C551 peroxidase warrants further study. This study suggests a phenotypic target candidate for interventions and genetic markers for the phenotype, which should be investigated further with the final aim of developing control strategies against C. jejuni infections.

The Rho-Independent Transcription Terminator for the porA Gene Enhances Expression of the Major Outer Membrane Protein and Campylobacter jejuni Virulence in Abortion Induction

Campylobacter jejuni is a leading cause of foodborne illnesses worldwide. Its porA gene encodes the major outer membrane protein (MOMP) that is abundantly expressed and has important physiological functions, including a key role in systemic infection and abortion induction in pregnant animals. Despite the importance of porA in C. jejuni pathogenesis, mechanisms modulating its expression levels remain elusive. At the 3' end of the porA transcript, there is a Rho-independent transcription terminator (named T _porA in this study). Whether T _porA affects the expression and function of MOMP remains unknown and is investigated in this study. Green fluorescent protein (GFP) fusion constructs with the porA promoter at the 5' end and an intact T _porA or no T _porA at the 3' end of the gfp coding sequence revealed that both the transcript level of gfp and its fluorescence signals were more than 2-fold higher in the construct with T _porA than in the one without T _porA Real-time quantitative PCR (qRT-PCR) analysis of the porA mRNA and immunoblot detection of MOMP in C. jejuni showed that disruption of T _porA significantly reduced the porA transcript level and the expression of MOMP. An mRNA decay assay demonstrated that disruption of T _porA resulted in a shortened transcript half-life of the upstream gfp or porA gene, indicating that T _porA enhances mRNA stability. In the guinea pig model, the C. jejuni construct with an interrupted T _porA was significantly attenuated in abortion induction. Together, these results indicate that T _porA enhances the expression level of MOMP by stabilizing its mRNA and influences the virulence of C. jejuni.

Sub-lethal antimicrobial photodynamic inactivation affects Pseudomonas aeruginosa PAO1 quorum sensing and cyclic di-GMP regulatory systems

BACKGROUND

Antimicrobial photodynamic inactivation (APDI) is a new therapeutic modality which needs more precision during application due to the possibility of exposure of bacteria to sub-lethal doses (sAPDI). In this study, we aimed to evaluate the effect of sAPDI on Pseudomonas aeruginosa quorum sensing (QS) and c-di-GMP signaling which are important virulence factor regulatory systems.

METHODS

Biofilm formation, pyoverdine, pyocyanin and protease production of P. aeruginosa was evaluated before and after a single sAPDI treatment with 0.8 mM methylene blue (MB) plus 1, 2, and 5-min irradiation with red laser light. Fluorescent lasB, rhlA, pqsA, and cdrA reporters of P. aeruginosa PAO1 and P. aeruginosa ΔmexAB-oprM were treated individually with sAPDI and the regulatory signals were detected. The gene expressions were also assessed after sAPDI using quantitative real-time PCR analysis.

RESULTS

Morphological observations and molecular assessments indicated that sAPDI with 0.8 mM MB along with 2- and 5-min irradiation led to an increase in the expression of the Las QS system and c-di-GMP signaling, while 1 min irradiation revealed dissimilar results (increase in lasB expression and decrease in c-di-GMP levels). Expression of rhlA and pqsA did not change in response to sAPDI. Further, a severe lethal effect of sAPDI was observed in P. aeruginosa ΔmexAB-oprM as compared with the wild type strain, whilst there was no difference in QS and c-di-GMP levels as detected by reporters between treated and untreated samples.

CONCLUSION

The results suggest that sAPDI affects QS and c-di-GMP signaling inP. aeruginosa in a time-dependent manner.

Phototrophic marine benthic microbiomes: the ecophysiology of these biological entities

Phototrophic biofilms are multispecies, self-sustaining and largely closed microbial ecosystems. They form macroscopic structures such as microbial mats and stromatolites. These sunlight-driven consortia consist of a number of functional groups of microorganisms that recycle the elements internally. Particularly, the sulfur cycle is discussed in more detail as this is fundamental to marine benthic microbial communities and because recently exciting new insights have been obtained. The cycling of elements demands a tight tuning of the various metabolic processes and require cooperation between the different groups of microorganisms. This is likely achieved through cell-to-cell communication and a biological clock. Biofilms may be considered as a macroscopic biological entity with its own physiology. We review the various components of some marine phototrophic biofilms and discuss their roles in the system. The importance of extracellular polymeric substances (EPS) as the matrix for biofilm metabolism and as substrate for biofilm microorganisms is discussed. We particularly assess the importance of extracellular DNA, horizontal gene transfer and viruses for the generation of genetic diversity and innovation, and for rendering resilience to external forcing to these biological entities.

The VicRK System of Streptococcus mutans Responds to Oxidative Stress

In Streptococcus mutans, virulence and cariogenicity may be modulated via the two-component regulatory system VicRK. Environmental signals, sensed by VicK, inducing this modulation are still unclear, however, and were investigated in the present study. We found that VicRK displays homology with protein-domains that, in other bacteria, are involved in redox-sensing. After constructing a VicRK-promoter GFP-reporter strain, we showed increased fluorescence intensity under oxidative stress. Potential interference of alternative signals and experimental conditions on GFP expression was excluded by the use of negative and positive control strains. Finally, we constructed a clean vicK knockout mutant, which proved to be more sensitive to H2O2 than the wild-type. In conclusion, this study showed that the VicRK system responds to and protects against oxidative stress. As a result, a link between oxidative/redox stress and the cariogenic nature of S. mutans can be hypothesized.

Mechanistic lessons learned from studies of planktonic bacteria with metallic nanomaterials: implications for interactions between nanomaterials and biofilm bacteria

Metal and metal-oxide nanoparticles (NPs) are used in numerous applications and have high likelihood of entering engineered and natural environmental systems. Careful assessment of the interaction of these NPs with bacteria, particularly biofilm bacteria, is necessary. This perspective discusses mechanisms of NP interaction with bacteria and identifies challenges in understanding NP-biofilm interaction, considering fundamental material attributes and inherent complexities of biofilm structure. The current literature is reviewed, both for planktonic bacteria and biofilms; future challenges and complexities are identified, both in light of the literature and a dataset on the toxicity of silver NPs toward planktonic and biofilm bacteria. This perspective aims to highlight the complexities in such studies and emphasizes the need for systematic evaluation of NP-biofilm interaction.

Proteomics dedicated to biofilmology: What have we learned from a decade of research?

Advances in proteomics techniques over the past decade, closely integrated with genomic and physicochemical approach, have played a great role in developing knowledge of the biofilm lifestyle of bacteria. Despite bacterial proteome versatility, many studies have demonstrated the ability of proteomics approaches to elucidating the biofilm phenotype. Though these investigations have been largely used for biofilm studies in the last decades, they represent, however, a very low percentage of proteomics works performed up to now. Such approaches have offered new targets for combating microbial biofilms by providing a comprehensive quantitative and qualitative overview of their protein cell content. Herein, we summarized the state of the art in knowledge about biofilm physiology after one decade of proteomic analysis. In a second part, we highlighted missing research tracks for the next decade, emphasizing the emergence of posttranslational modifications in proteomic studies stemming from recent advances in mass spectrometry-based proteomics.

Nitrate and periplasmic nitrate reductases

The nitrate anion is a simple, abundant and relatively stable species, yet plays a significant role in global cycling of nitrogen, global climate change, and human health. Although it has been known for quite some time that nitrate is an important species environmentally, recent studies have identified potential medical applications. In this respect the nitrate anion remains an enigmatic species that promises to offer exciting science in years to come. Many bacteria readily reduce nitrate to nitrite via nitrate reductases. Classified into three distinct types--periplasmic nitrate reductase (Nap), respiratory nitrate reductase (Nar) and assimilatory nitrate reductase (Nas), they are defined by their cellular location, operon organization and active site structure. Of these, Nap proteins are the focus of this review. Despite similarities in the catalytic and spectroscopic properties Nap from different Proteobacteria are phylogenetically distinct. This review has two major sections: in the first section, nitrate in the nitrogen cycle and human health, taxonomy of nitrate reductases, assimilatory and dissimilatory nitrate reduction, cellular locations of nitrate reductases, structural and redox chemistry are discussed. The second section focuses on the features of periplasmic nitrate reductase where the catalytic subunit of the Nap and its kinetic properties, auxiliary Nap proteins, operon structure and phylogenetic relationships are discussed.

Role of environmental survival in transmission of Campylobacter jejuni

Campylobacter species are the most common cause of bacterial gastroenteritis, with C. jejuni responsible for the majority of these cases. Although it is clear that livestock, and particularly poultry, are the most common source, it is likely that the natural environment (soil and water) plays a key role in transmission, either directly to humans or indirectly via farm animals. It has been shown using multilocus sequence typing that some clonal complexes (such as ST-45) are more frequently isolated from environmental sources such as water, suggesting that strains vary in their ability to survive in the environment. Although C. jejuni are fastidious microaerophiles generally unable to grow in atmospheric levels of oxygen, C. jejuni can adapt to survival in the environment, exhibiting aerotolerance and starvation survival. Biofilm formation, the viable but nonculturable state, and interactions with other microorganisms can all contribute to survival outside the host. By exploiting high-throughput technologies such as genome sequencing and RNA Seq, we are well placed to decipher the mechanisms underlying the variations in survival between strains in environments such as soil and water and to better understand the role of environmental persistence in the transmission of C. jejuni directly or indirectly to humans.

The CJIE1 prophage of Campylobacter jejuni affects protein expression in growth media with and without bile salts

BACKGROUND

The presence of Campylobacter jejuni temperate bacteriophages has increasingly been associated with specific biological effects. It has recently been demonstrated that the presence of the prophage CJIE1 is associated with increased adherence and invasion of C. jejuni isolates in cell culture assays.

RESULTS

Quantitative comparative proteomics experiments were undertaken using three closely related isolates with CJIE1 and one isolate without CJIE1 to determine whether there was a corresponding difference in protein expression levels. Initial experiments indicated that about 2% of the total proteins characterized were expressed at different levels in isolates with or without the prophage. Some of these proteins regulated by the presence of CJIE1 were associated with virulence or regulatory functions. Additional experiments were conducted using C. jejuni isolates with and without CJIE1 grown on four different media: Mueller Hinton (MH) media containing blood; MH media containing 0.1% sodium deoxycholate, which is thought to result in increased expression of virulence proteins; MH media containing 2.5% Oxgall; and MHwithout additives. These experiments provided further evidence that CJIE1 affected protein expression, including virulence-associated proteins. They also demonstrated a general bile response involving a majority of the proteome and clearly showed the induction of almost all proteins known to be involved with iron acquisition. The data have been deposited to the ProteomeXchange with identifiers PXD000798, PXD000799, PXD000800, and PXD000801.

CONCLUSION

The presence of the CJIE1 prophage was associated with differences in protein expression levels under different conditions. Further work is required to determine what genes are involved in causing this phenomenon.

The complete Campylobacter jejuni transcriptome during colonization of a natural host determined by RNAseq

Campylobacter jejuni is a major human pathogen and a leading cause of bacterial derived gastroenteritis worldwide. C. jejuni regulates gene expression under various environmental conditions and stresses, indicative of its ability to survive in diverse niches. Despite this ability to highly regulate gene transcription, C. jejuni encodes few transcription factors and its genome lacks many canonical transcriptional regulators. High throughput deep sequencing of mRNA transcripts (termed RNAseq) has been used to study the transcriptome of many different organisms, including C. jejuni; however, this technology has yet to be applied to defining the transcriptome of C. jejuni during in vivo colonization of its natural host, the chicken. In addition to its use in profiling the abundance of annotated genes, RNAseq is a powerful tool for identifying and quantifying, as-of-yet, unknown transcripts including non-coding regulatory RNAs, 5’ untranslated regulatory elements, and anti-sense transcripts. Here we report the complete transcriptome of C. jejuni during colonization of the chicken cecum and in two different in vitro growth phases using strand-specific RNAseq. Through this study, we identified over 250 genes differentially expressed in vivo in addition to numerous putative regulatory RNAs, including trans-acting non-coding RNAs and anti-sense transcripts. These latter potential regulatory elements were not identified in two prior studies using ORF-based microarrays, highlighting the power and value of the RNAseq approach. Our results provide new insights into how C. jejuni responds and adapts to the cecal environment and reveals new functions involved in colonization of its natural host.

Role of capsular polysaccharides and lipooligosaccharides in Campylobacter surface properties, autoagglutination, and attachment to abiotic surfaces

The role of capsular polysaccharides and lipooligosaccharides in cell surface hydrophobicity, surface charge, autoagglutination (AAG), and attachment to abiotic surfaces of three strains of Campylobacter jejuni and one strain of C. coli were investigated. This was achieved by removal of capsular polysaccharides and truncation of lipooligosaccharides core oligosaccharides by inactivation of the kpsE and waaF genes, respectively. The mutants and the wild-type strains were compared after growth under planktonic (broth) and sessile (agar) conditions. Cells grown as planktonic cultures showed a significantly (p<0.05) higher degree of hydrophobicity and AAG activity but differed from their sessile counterparts with respect to surface charge and attachment counts, depending on the strain. These results suggest that prior mode of growth affects the surface properties and attachment of Campylobacter in a strain-dependent manner. There were no significant (p>0.05) differences between the three C. jejuni strains and their ΔkpsE and ΔwaaF mutants with respect to all traits tested. Inactivation of the kpsE gene significantly (p<0.05) reduced the surface charge of the C. coli strain from ∼-10 to ∼-6 mV and increased its AAG activity, while disruption of the waaF gene significantly (p<0.05) increased its surface hydrophobicity by >8° and decreased the numbers of cells attaching to stainless steel and glass by ∼0.5 log/cm². These results suggest that surface polysaccharides may influence the surface properties and attachment to abiotic surfaces of C. coli but not C. jejuni. This suggestion, however, requires further investigation using a larger number of strains of both species.

Differential protein expression patterns between planktonic and biofilm cells of Salmonella enterica serovar Enteritidis PT4 on stainless steel surface

In the present study, the proteome of a strain of S. enterica serovar Enteritidis PT4, grown either as biofilm on stainless steel surface or as free-floating (planktonic) in Brain Heart (BH) broth, was investigated in order to detect the strong differences in whole-cell protein expression patterns between the two growth styles. The proteins extracted from both types of cells were subjected to 2-D PAGE, followed by in-gel tryptic digestion, extraction, subsequent MALDI-TOF mass spectrometry (MS) analysis and finally database searches for protein identification. Using this approach, 30 proteins were identified as differentially expressed between the two growth modes on an "on-off" basis, that is, proteins that were detected in one case but not in the other. In particular, 20 and 10 proteins were identified in biofilm and planktonic-grown cells, respectively. The group of proteins whose expression was visible only during biofilm growth included proteins involved in global regulation and stress response (ArcA, BtuE, Dps, OsmY, SspA, TrxA, YbbN and YhbO), nutrient transport (Crr, DppA, Fur and SufC), degradation and energy metabolism (GcvT, GpmA, RibB), detoxification (SseA and YibF), DNA metabolism (SSB), curli production (CsgF), and murein synthesis (MipA). To summarize, this study demonstrates that biofilm growth of S. Enteritidis causes distinct changes in protein expression and offers valuable new data regarding some of the proteins presumably involved in this process. The putative role of these proteins in the maintenance of a biofilm community in Salmonella and other bacteria is discussed.

Biofilm growth and near-infrared radiation-driven photosynthesis of the chlorophyll d-containing cyanobacterium Acaryochloris marina

The cyanobacterium Acaryochloris marina is the only known phototroph harboring chlorophyll (Chl) d. It is easy to cultivate it in a planktonic growth mode, and A. marina cultures have been subject to detailed biochemical and biophysical characterization. In natural situations, A. marina is mainly found associated with surfaces, but this growth mode has not been studied yet. Here, we show that the A. marina type strain MBIC11017 inoculated into alginate beads forms dense biofilm-like cell clusters, as in natural A. marina biofilms, characterized by strong O(2) concentration gradients that change with irradiance. Biofilm growth under both visible radiation (VIS, 400 to 700 nm) and near-infrared radiation (NIR, ∼700 to 730 nm) yielded maximal cell-specific growth rates of 0.38 per day and 0.64 per day, respectively. The population doubling times were 1.09 and 1.82 days for NIR and visible light, respectively. The photosynthesis versus irradiance curves showed saturation at a photon irradiance of E(k) (saturating irradiance) >250 μmol photons m(-2) s(-1) for blue light but no clear saturation at 365 μmol photons m(-2) s(-1) for NIR. The maximal gross photosynthesis rates in the aggregates were ∼1,272 μmol O(2) mg Chl d(-1) h(-1) (NIR) and ∼1,128 μmol O(2) mg Chl d(-1) h(-1) (VIS). The photosynthetic efficiency (α) values were higher in NIR-irradiated cells [(268 ± 0.29) × 10(-6) m(2) mg Chl d(-1) (mean ± standard deviation)] than under blue light [(231 ± 0.22) × 10(-6) m(2) mg Chl d(-1)]. A. marina is well adapted to a biofilm growth mode under both visible and NIR irradiance and under O(2) conditions ranging from anoxia to hyperoxia, explaining its presence in natural niches with similar environmental conditions.

A third mode of surface-associated growth: immobilization of Salmonella enterica serovar Typhimurium modulates the RpoS-directed transcriptional programme

Although the growth of bacteria has been studied for more than a century, it is only in recent decades that surface-associated growth has received attention. In addition to the well-characterized biofilm and swarming lifestyles, bacteria can also develop as micro-colonies supported by structured environments in both food products and the GI tract. This immobilized mode of growth has not been widely studied. To develop our understanding of the effects of immobilization upon a food-borne bacterial pathogen, we used the IFR Gel Cassette model. The transcriptional programme and metabolomic profile of Salmonella enterica serovar Typhimurium ST4/74 were compared during planktonic and immobilized growth, and a number of immobilization-specific characteristics were identified. Immobilized S.Typhimurium did not express motility and chemotaxis genes, and electron microscopy revealed the absence of flagella. The expression of RpoS-dependent genes and the level of RpoS protein were increased in immobilized bacteria, compared with planktonic growth. Immobilized growth prevented the induction of SPI1, SPI4 and SPI5 gene expression, likely mediated by the FliZ transcriptional regulator. Using an epithelial cell-based assay, we showed that immobilized S.Typhimurium was significantly less invasive than planktonic bacteria, and we suggest that S.Typhimurium grown in immobilized environments are less virulent than planktonic bacteria. Our findings identify immobilization as a third type of surface-associated growth that is distinct from the biofilm and swarming lifestyles of Salmonella.

Altered expression level of Escherichia coli proteins in response to treatment with the antifouling agent zosteric acid sodium salt

Zosteric acid sodium salt is a powerful antifouling agent. However, the mode of its antifouling action has not yet been fully elucidated. Whole cell proteome of Escherichia coli was analysed to study the different protein patterns expressed by the surface-exposed planktonic cells without and with sublethal concentrations of the zosteric acid sodium salt. Proteomic analysis revealed that at least 27 proteins showed a significant (19 upregulated and 8 downregulated, P < 0.001) altered expression level in response to the antifoulant. The proteomic signatures of zosteric acid sodium salt-treated cells are characterized by stress-associated (e.g. AhpC, OsmC, SodB, GroES, IscU, DnaK), motility-related (FliC), quorum-sensing-associated (LuxS) and metabolism/biosynthesis-related (e.g. PptA, AroA, FabD, FabB, GapA) proteins. Consistent with the overexpression of LuxS enzyme, the antifouling agent increased autoinducer-2 (AI-2) concentration by twofold. Moreover, treated cells experienced a statistically significant but modest increase of reactive oxygen species (+ 23%), tryptophanase (1.2-fold) and indole (1.2-fold) synthesis. Overall, our data suggest that zosteric acid sodium salt acts as environmental cue leading to global stress on E. coli cells, which favours the expression of various protective proteins, the AI-2 production and the synthesis of flagella, to escape from adverse conditions.

Campylobacter jejuni dsb gene expression is regulated by iron in a Fur-dependent manner and by a translational coupling mechanism

BACKGROUND

Many bacterial extracytoplasmic proteins are stabilized by intramolecular disulfide bridges that are formed post-translationally between their cysteine residues. This protein modification plays an important role in bacterial pathogenesis, and is facilitated by the Dsb (disulfide bond) family of the redox proteins. These proteins function in two parallel pathways in the periplasmic space: an oxidation pathway and an isomerization pathway. The Dsb oxidative pathway in Campylobacter jejuni is more complex than the one in the laboratory E. coli K-12 strain.

RESULTS

In the C. jejuni 81-176 genome, the dsb genes of the oxidative pathway are arranged in three transcriptional units: dsbA2-dsbB-astA, dsbA1 and dba-dsbI. Their transcription responds to an environmental stimulus - iron availability - and is regulated in a Fur-dependent manner. Fur involvement in dsb gene regulation was proven by a reporter gene study in a C. jejuni wild type strain and its isogenic fur mutant. An electrophoretic mobility shift assay (EMSA) confirmed that analyzed genes are members of the Fur regulon but each of them is regulated by a disparate mechanism, and both the iron-free and the iron-complexed Fur are able to bind in vitro to the C. jejuni promoter regions. This study led to identification of a new iron- and Fur-regulated promoter that drives dsbA1 gene expression in an indirect way. Moreover, the present work documents that synthesis of DsbI oxidoreductase is controlled by the mechanism of translational coupling. The importance of a secondary dba-dsbI mRNA structure for dsbI mRNA translation was verified by estimating individual dsbI gene expression from its own promoter.

CONCLUSIONS

The present work shows that iron concentration is a significant factor in dsb gene transcription. These results support the concept that iron concentration - also through its influence on dsb gene expression - might control the abundance of extracytoplasmic proteins during different stages of infection. Our work further shows that synthesis of the DsbI membrane oxidoreductase is controlled by a translational coupling mechanism. The dba expression is not only essential for the translation of the downstream dsbI gene, but also Dba protein that is produced might regulate the activity and/or stability of DsbI.

Comparative proteomic analysis of biofilm and planktonic cells of Neisseria meningitidis

Neisseria meningitidis is a commensal of the human nasopharynx occasionally causing invasive disease. In vitro biofilms have been employed to model meningococcal carriage. A proteomic analysis of meningococcal biofilms was conducted and metabolic changes related to oxygen and nutrient limitation and upregulation of proteins involved in ROS defense were observed. The upregulated MntC which protects against ROS was shown to be required for meningococcal biofilm formation, but not for planktonic growth. ROS-induced proteomic changes might train the biofilm to cope with immune effectors.

Eight enrichment broths for the isolation of Campylobacter jejuni from inoculated suspensions and ground pork

AIMS

The efficiency of eight enrichment broths for the selective isolation of Campylobacter jejuni was compared to identify an optimal enrichment broth.

METHODS AND RESULTS

Brucella-FBP, Preston, Doyle and Roman, modified CCD (mCCD), Park and Sanders, Bolton, Hunt and Radle and Hunt broths were compared for their recovery of (i) Camp. jejuni in suspension, (ii) Camp. jejuni from inoculated ground pork, (iii) heat-injured Camp. jejuni (55 degrees C for 20 min) in suspension and (iv) heat-injured Camp. jejuni from inoculated ground pork. Hunt broth and Bolton broth showed the highest and most rapid enrichment efficacy for the cell suspensions and ground pork, respectively. Preston, Park and Sanders and mCCD broths had relatively high enrichment efficiencies, while Brucella-FBP broth was significantly inferior to the other broths (P < 0.05).

CONCLUSIONS

Cell recovery from the eight enrichment broths was dependent on the sample type and the state of the cells. The use of the appropriate broth is important for the rapid and efficacious enrichment of Camp. jejuni. In particular, heat-injured Camp. jejuni require a longer cultivation time and a suitable enrichment broth.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results from the present study provide information for selecting the most appropriate enrichment broth for Camp. jejuni and may contribute to improved detection methods for the organism.

Campylobacter biofilm phenotype exhibits reduced colonization potential in young chickens and altered in vitro virulence

In this study, we evaluated the ability of different Campylobacter phenotypes (biofilm versus planktonic) to colonize young poultry. It has been suggested that a persistent Campylobacter biofilm reservoir may be involved in the initial contamination of poultry flocks. Campylobacter jejuni cultured adherent to agar was utilized as the biofilm model and C. jejuni cultured in broth was evaluated as the planktonic model. In 2 independent trials, 1-d-old broiler chicks were given 1 of 3 treatments: 1) 10(5) cfu.mL(-1) of C. jejuni cultured in broth, 2) 10(5) cfu.mL(-1) of C. jejuni cultured adherent to agar, or 3) no C. jejuni (negative control). Cecal contents of all birds were evaluated by culturing 12 d after the initial challenge with C. jejuni. In both trials, birds challenged with C. jejuni cultured in broth had approximately 3 to 4 log higher cecal Campylobacter concentration than birds challenged with C. jejuni cultured adherent to agar. Using 2 cell lines (INT 407 and DF1), virulence of C. jejuni cultured in broth versus adherent to agar also was evaluated by challenging monolayers of eukaryotic cells with 1 of 3 treatments: 1) 10(5) cfu.mL(-1) of C. jejuni cultured in broth, 2) 10(5) cfu.mL(-1) of C. jejuni cultured adherent to agar, or 3) no C. jejuni (negative control). The virulence study also showed differences of C. jejuni cultured in broth or agar in attachment and invasion abilities to tissue culture cells, but differences were not as consistent as with the chick colonization study. This study indicates that phenotype may play a role in colonization of chickens and virulence by C. jejuni.

Campylobacter proteomics: guidelines, challenges and future perspectives

Campylobacter species are a major cause of disease in mammalian systems. The most common human etiological agent within this genus is Campylobacter jejuni - the leading cause of bacterial gastroenteritis in the developed world. While this organism has been extensively studied at the cellular level, and the genome sequences of several strains have now been elucidated, little is known regarding the role of individual proteins in virulence processes, such as adhesion, colonization and toxicity towards host cells. Proteomics encompasses the global analysis of proteins at the organism level. The technologies included under this term have now started to be utilized for understanding how Campylobacter species respond to changes in the environment, with an emphasis on the human host, as well as to map subcellular locations of proteins, in particular those that are surface-associated. C. jejuni is also of great significance as, unlike most other bacteria, it is able to post-translationally modify its proteins. The analysis of such proteins represents a major challenge in understanding this organism at the proteomic and cellular levels. This review will examine the state-of-the-art in Campylobacter proteomics, as well as provide insights into strategies that need to be undertaken to provide a comprehensive understanding of this organism at the molecular and functional level.

Update on Campylobacter jejuni vaccine development for preventing human campylobacteriosis

Campylobacteriosis constitutes a serious medical and socioeconomic problem worldwide. Rapidly increasing antibiotic resistance of bacterial strains compels us to develop alternative therapeutic strategies and to search for efficient immunoprophylactic methods. The vast majority of Campylobacter infections in developed countries occur as sporadic cases, mainly caused by eating undercooked Campylobacter-contaminated poultry. The most efficient strategy of decreasing the number of human Campylobacter infections is by implementing protective vaccinations for humans and/or chickens. Despite more than 10 years of research, an effective anti-Campylobacter vaccine has not been developed. This review highlights our increasing knowledge of Campylobacter interaction with host cells and focuses on recently published data describing the efficacy of anti-Campylobacter vaccine prototypes.

The OxyR homologue in Tannerella forsythia regulates expression of oxidative stress responses and biofilm formation

Tannerella forsythia is an anaerobic periodontal pathogen that encounters constant oxidative stress in the human oral cavity due to exposure to air and reactive oxidative species from coexisting dental plaque bacteria as well as leukocytes. In this study, we sought to characterize a T. forsythia ORF with close similarity to bacterial oxidative stress response sensor protein OxyR. To analyse the role of this OxyR homologue, a gene deletion mutant was constructed and characterized. Aerotolerance, survival after hydrogen peroxide challenge and transcription levels of known bacterial antioxidant genes were then determined. Since an association between oxidative stress and biofilm formation has been observed in bacterial systems, we also investigated the role of the OxyR protein in biofilm development by T. forsythia. Our results showed that aerotolerance, sensitivity to peroxide challenge and the expression of oxidative stress response genes were significantly reduced in the mutant as compared with the wild-type strain. Moreover, the results of biofilm analyses showed that, as compared with the wild-type strain, the oxyR mutant showed significantly less autoaggregation and a reduced ability to form mixed biofilms with Fusobacterium nucleatum. In conclusion, a gene annotated in the T. forsythia genome as an oxyR homologue was characterized. Our studies showed that the oxyR homologue in T. forsythia constitutively activates antioxidant genes involved in resistance to peroxides as well as oxygen stress (aerotolerance). In addition, the oxyR deletion attenuates biofilm formation in T. forsythia.

The CprS sensor kinase of the zoonotic pathogen Campylobacter jejuni influences biofilm formation and is required for optimal chick colonization

Campylobacter jejuni, a prevalent cause of bacterial gastroenteritis, must adapt to different environments to be a successful pathogen. We previously identified a C. jejuni two-component regulatory system (Cj1226/7c) as upregulated during cell infections. Analyses described herein led us to designate the system CprRS (Campylobacter planktonic growth regulation). While the response regulator was essential, a cprS sensor kinase mutant was viable. The Delta cprS mutant displayed an apparent growth defect and formed dramatically enhanced and accelerated biofilms independent of upregulation of previously characterized surface polysaccharides. Delta cprS also displayed a striking dose-dependent defect for colonization of chicks and was modestly enhanced for intracellular survival in INT407 cells. Proteomics analyses identified changes consistent with modulation of essential metabolic genes, upregulation of stress tolerance proteins, and increased expression of MOMP and FlaA. Consistent with expression profiling, we observed enhanced motility and secretion in Delta cprS, and decreased osmotolerance and oxidative stress tolerance. We also found that C. jejuni biofilms contain a DNase I-sensitive component and that biofilm formation is influenced by deoxycholate and the metabolic substrate fumarate. These results suggest that CprRS influences expression of factors important for biofilm formation, colonization and stress tolerance, and also add to our understanding of C. jejuni biofilm physiology.

Role of the Cj1371 periplasmic protein and the Cj0355c two-component regulator in the Campylobacter jejuni NCTC 11168 response to oxidative stress caused by paraquat

Campylobacter jejuni is a microaerophilic pathogen representing one of the major causes of bacterial enteritis in humans. The oxidative stress response after exposure to paraquat, a strong oxidising agent, was analysed by two-dimensional protein electrophoresis and Maldi-ToF mass spectrometry. Oxidative stress and redox-related proteins were overexpressed: FldA flavodoxin and a pyruvate-flavodoxin oxidoreductase encoded by cj1476c. No increase in SodB expression was observed. An additional quantitative RT-PCR analysis showed an increase in katA but not in sodB expression. However, the sodB mutant was very sensitive to paraquat, its basal expression level being essential for oxidative stress resistance. Proteins related to iron homeostasis (Cft and a non-haem iron protein encoded by cj0012c) and general stress response (FusA and MreB) were found overexpressed. Interestingly, a two-component regulator encoded by cj0355c was differentially expressed in the presence of paraquat and could play a role in induction of the C. jejuni oxidative stress response. Virulence factors (CadF, FlaA and a VacJ homolog encoded by cj1371) were also found overexpressed under oxidative stress conditions and a cj1371 mutant showed increased sensitivity to paraquat, suggesting that the Cj1371 periplasmic protein could play a role in C. jejuni oxidative stress resistance.

Campylobacter jejuni response to human mucin MUC2: modulation of colonization and pathogenicity determinants

Campylobacter jejuni is the main cause of bacterial acute gastroenteritis worldwide. In its colonization of the host intestinal tract, it encounters secreted mucins in the mucus layer and surface mucins in the epithelial cells. Mucins are complex glycoproteins that comprise the major component of mucus and give mucus its viscous consistency. MUC2 is the most abundant secreted mucin in the human intestine; it is a major chemoattractant for C. jejuni, and the bacterium binds to it. There are no studies on the transcriptional response of the bacterium to this mucin. Here, cell-culture techniques and quantitative RT-PCR were used to characterize in vitro the effects of MUC2 on C. jejuni growth and the changes in expression of 20 C. jejuni genes related to various functions. The genes encoding cytolethal distending toxin protein (cdtABC), vacuolating cytotoxin (vacB), C. jejuni lipoprotein (jlpA), Campylobacter invasion antigen (ciaB), the multidrug efflux system (cmeAB), putative mucin-degrading enzymes (cj1344c, cj0843c, cj0256 and cj1055c), flagellin A (flaA) and putative rod-shape-determining proteins (mreB and mreC) were upregulated, whereas those encoding Campylobacter adhesion fibronectin-binding protein (cadF) and sialic acid synthase (neuB1) were downregulated. These results showed that C. jejuni utilizes MUC2 as an environmental cue for the modulation of expression of genes with various functions including colonization and pathogenicity.

Autoinducer-2 triggers the oxidative stress response in Mycobacterium avium, leading to biofilm formation

Mycobacterium avium is an environmental organism and opportunistic pathogen with inherent resistance to drugs, environmental stresses, and the host immune response. To adapt to these disparate conditions, M. avium must control its transcriptional response to environmental cues. M. avium forms biofilms in various environmental settings, including drinking water pipes and potable water reservoirs. In this study, we investigated the role of the universal signaling molecule autoinducer-2 (AI-2) in biofilm formation by M. avium. The addition of the compound to planktonic M. avium cultures resulted in increased biofilm formation. Microarray and reverse transcriptase PCR studies revealed an upregulation of the oxidative stress response upon addition of AI-2. This suggests that the response to AI-2 might be related to oxidative stress, rather than quorum sensing. Consistent with this model, addition of hydrogen peroxide, a known stimulus of the oxidative stress response, to M. avium cultures resulted in elevated biofilm formation. These results suggest that AI-2 does not act as a quorum-sensing signal in M. avium. Instead, biofilm formation is triggered by environmental stresses of biotic and abiotic origins and AI-2 may exert effects on that level.

Campylobacter jejuni biofilms up-regulated in the absence of the stringent response utilize a calcofluor white-reactive polysaccharide

The enteric pathogen Campylobacter jejuni is a highly prevalent yet fastidious bacterium. Biofilms and surface polysaccharides participate in stress survival, transmission, and virulence in C. jejuni; thus, the identification and characterization of novel genes involved in each process have important implications for pathogenesis. We found that C. jejuni reacts with calcofluor white (CFW), indicating the presence of surface polysaccharides harboring beta1-3 and/or beta1-4 linkages. CFW reactivity increased with extended growth, under 42 degrees C anaerobic conditions, and in a DeltaspoT mutant defective for the stringent response (SR). Conversely, two newly isolated dim mutants exhibited diminished CFW reactivity as well as growth and serum sensitivity differences from the wild type. Genetic, biochemical, and nuclear magnetic resonance analyses suggested that differences in CFW reactivity between wild-type and DeltaspoT and dim mutant strains were independent of well-characterized lipooligosaccharides, capsular polysaccharides, and N-linked polysaccharides. Targeted deletion of carB downstream of the dim13 mutation also resulted in CFW hyporeactivity, implicating a possible role for carbamoylphosphate synthase in the biosynthesis of this polysaccharide. Correlations between biofilm formation and production of the CFW-reactive polymer were demonstrated by crystal violet staining, scanning electron microscopy, and confocal microscopy, with the C. jejuni DeltaspoT mutant being the first SR mutant in any bacterial species identified as up-regulating biofilms. Together, these results provide new insight into genes and processes important for biofilm formation and polysaccharide production in C. jejuni.

Proteomic analyses of a robust versus a poor chicken gastrointestinal colonizing isolate of Campylobacter jejuni

Campylobacter spp. are a significant contributor to the bacterial etiology of acute gastroenteritis in humans. Epidemiological evidence implicates poultry as a major source of the organism for human illness. However, the factors involved in colonization of poultry with Campylobacter spp. remain unclear. Determining colonization-associated factors at the proteome level should facilitate our understanding of Campylobacter spp. contamination of poultry. Therefore, proteomic analyses were utilized to identify expression differences between two Campylobacter jejuni isolates, a robust colonizer A74/C and a poor colonizing strain of the chicken gastrointestinal system designated NCTC 11168-PMSRU. Proteomic analyses by two-dimensional gel electrophoresis revealed the specific expression of an outer membrane-fibronectin binding protein, serine protease, and a putative aminopeptidase in the soluble portion of the robust colonizer A74C. Several proteins including a cysteine synthase and aconitate hydratase were detected specifically in the poor colonizer C. jejuni NCTC 11168-PMSRU isolate. Variation in the amino acid sequences resulting in different isoelectric points and relative mobility of the flagellin and C. jejuni major outer membrane (MOMP) protein were also detected between the two isolates. Western blotting of the bacterial proteins revealed the presence of two flagellin proteins in the poor colonizer versus one in the robust colonizing isolate, but no differences in MOMP. The results demonstrated that proteomics is useful for characterizing phenotypic variation among Campylobacter spp. isolates. Interestingly, different gene products potentially involved in robust colonization of chickens by Campylobacter spp. appear to conform to recently identified expression patterns in Biofilm or agar-adapted isolates.

The role of iron in Mycobacterium smegmatis biofilm formation: the exochelin siderophore is essential in limiting iron conditions for biofilm formation but not for planktonic growth

Many species of mycobacteria form structured biofilm communities at liquid–air interfaces and on solid surfaces. Full development of Mycobacterium smegmatis biofilms requires addition of supplemental iron above 1 μM ferrous sulphate, although addition of iron is not needed for planktonic growth. Microarray analysis of the M. smegmatis transcriptome shows that iron-responsive genes – especially those involved in siderophore synthesis and iron uptake – are strongly induced during biofilm formation reflecting a response to iron deprivation, even when 2 μM iron is present. The acquisition of iron under these conditions is specifically dependent on the exochelin synthesis and uptake pathways, and the strong defect of an iron–exochelin uptake mutant suggests a regulatory role of iron in the transition to biofilm growth. In contrast, although the expression of mycobactin and iron ABC transport operons is highly upregulated during biofilm formation, mutants in these systems form normal biofilms in low-iron (2 μM) conditions. A close correlation between iron availability and matrix-associated fatty acids implies a possible metabolic role in the late stages of biofilm maturation, in addition to the early regulatory role. M. smegmatis surface motility is similarly dependent on iron availability, requiring both supplemental iron and the exochelin pathway to acquire it.

Deletion of peb4 gene impairs cell adhesion and biofilm formation in Campylobacter jejuni

Campylobacter jejuni is a microaerophilic bacterium that causes diarrhea in humans. The first step in establishing an infection is adherence to a host cell, which involves two major cell-binding proteins, Peb1A (CBF1) and Peb4 (CBF2). Because the functional role of Peb4 on the cell adhesion remains unclear compared with that of Peb1A, a C. jejuni peb4 deletion mutant was constructed and cell adherence and ability to colonize mouse intestine were studied. The result showed that adherence of the peb4 mutant strain to INT407 cells was 1-2% that of the wild-type strain. Mouse challenge experiments showed a reduced level and duration of intestinal colonization by the mutant compared with the wild-type strain. In addition, fewer peb4 mutant cells than wild-type cells responded to stress by forming a biofilm. Proteomic analysis revealed that the expression levels of proteins involved in various adhesion, transport, and motility functions, which are required for biofilm formation by the pathogen, were lower in the peb4 mutant than in the wild-type strain. A Peb4 homolog has prolyl cis/trans-isomerase activity, suggesting that the loss of this activity in the mutant strain may be responsible for the repression of these proteins.

Culture and detection of Campylobacter jejuni within mixed microbial populations of biofilms on stainless steel

Campylobacter jejuni is the most frequently reported cause of foodborne illness in the United States, but its survival outside the host is poor. The objective of this research was to examine the formation and composition of biofilms by C. jejuni alone and within mixed bacterial populations from the poultry-processing environment. C. jejuni growth was assessed with four media, two temperatures, and two atmospheric conditions to develop culture methods for liquid media that would allow growth within the biofilms. Growth kinetics was followed at four cell densities to determine temporal compatibility within biofilm mixtures. Analysis of the biofilms by confocal laser scanning microscopy showed that C. jejuni formed a biofilm when incubated without other bacteria. The average surface area of stainless steel covered by C. jejuni increased by 50% from 24 to 48 h, remained level to 96 h, and then decreased by 88% by 168 h. C. jejuni and mixed bacterial populations formed biofilms during incubation periods of up to 7 days. The area of the mixture was significantly greater than for C. jejuni alone at 24 h, was approximately the same at 48 h, and was significantly less by 168 h. When incubated with either of two initial inoculum densities of other bacteria, the number of C. jejuni was enhanced after 24 h. The intensity of fluorescence and cell viability were monitored by epifluorescence microscopy. This study provides the basis for studying interactions of Campylobacter spp. with other bacteria in the environment, which will aid in the design of effective intervention strategies.

Media for the aerobic resuscitation of Campylobacter jejuni

The microaerophilic nature of Campylobacter jejuni has complicated its recovery from human and animal sources. In this study, enhancement of the growth and aerotolerance of C. jejuni ATCC 35921 in nutrient broth no. 2 (NB2) was investigated. The efficiency of recovery of C. jejuni in NB2 containing FBP (0.025% [each] ferrous sulfate, sodium metabisulfite, and sodium pyruvate), 5% laked horse blood, hemin, Oxyrase, or activated charcoal in an aerobic atmosphere was compared with that obtained under microaerophilic incubation. The shortest lag time (lamda) for cells grown aerobically was observed with NB2 supplemented with FBP, 5% laked horse blood, 0.01 g/liter of hemin, or 0.15 U/ml of Oxyrase. The efficacy of these media to resuscitate C. jejuni cells in late exponential phase, as well as cells subjected to stress induced by cold, heat, starvation, or acid, was determined in aerobic or microaerobic atmospheres. The h of cells grown aerobically in NB2 containing both FBP and blood was similar to that obtained in the same medium incubated in a microaerobic environment (P > 0.05). However, the X was longer during aerobic growth when low numbers of cells (approximately 1 log CFU/ml) in late exponential phase were used as the initial inoculum. The best recovery of stressed C. jejuni was observed in NB2 supplemented with FBP and blood and incubated aerobically. Enrichment in media incorporating FBP and 5% laked horse blood is a simple, convenient, and time-saving method to replace microaerophilic incubation methods for the resuscitation of C. jejuni.

Growth temperature of four Campylobacter jejuni strains influences their subsequent survival in food and water

AIM

To determine if Campylobacter jejuni grown at 37 and 42 degrees C have different abilities to survive on beef and chicken, and in water.

METHODS AND RESULTS

Beef, chicken and water were separately inoculated with four Camp. jejuni (two poultry and two beef) strains grown at 37 or 42 degrees C. The matrices were stored at approximately 4 degrees C and Camp. jejuni numbers were monitored over time by plate counts. On beef there was a greater decrease in number for two strains (P < 0.05; approximately 0.7 and 1.3 log CFU cm(-2)) grown at 37 degrees C as compared with 42 degrees C. By contrast on chicken there was a decrease in numbers for two strains (P < 0.05; approximately 1.3 and 1 log CFU g(-1)) grown at 42 degrees C as compared with 37 degrees C. In water there was a greater decrease in numbers for all strains (P < 0.05; approximately 3-5.3 log CFU ml(-1)) grown at 42 degrees C as compared with 37 degrees C.

CONCLUSIONS

Growth temperature influences the survival of Camp. jejuni on food and in water.

SIGNIFICANCE AND IMPACT OF THE STUDY

Campylobacter jejuni survival studies need to consider growth temperature to avoid erroneous results. Campylobacter jejuni grown at 37 degrees C, the body temperature of humans and cattle, may represent a greater public health risk in water than those grown at 42 degrees C, the body temperature of poultry.

The role of periplasmic antioxidant enzymes (superoxide dismutase and thiol peroxidase) of the Shiga toxin-producingEscherichia coli O157:H7 in the formation of biofilms

This study examined the role of the periplasmic oxidative defense proteins, copper, zinc superoxide dismutase (SodC), and thiol peroxidase (Tpx), from the Shiga toxin-producing Escherichia coli O157:H7 (STEC) in the formation of biofilms. Proteomic analyses have shown significantly higher expression levels of both periplasmic antioxidant systems (SodC and Tpx) in STEC cells grown under biofilm conditions than under planktonic conditions. An analysis of their growth phase-dependent gene expression indicated that a high level of the sodC expression occurred during the stationary phase and that the expression of the tpx gene was strongly induced only during the exponential growth phase. Exogenous hydrogen peroxide reduced the aerobic growth of the STEC sodC and tpx mutants by more than that of their parental strain. The two mutants also displayed significant reductions in their attachment to both biotic (HT-29 epithelial cell) and abiotic surfaces (polystyrene and polyvinyl chloride microplates) during static aerobic growth. However, the growth rates of both wild-type and mutants were similar under aerobic growth conditions. The formation of an STEC biofilm was only observed with the wild-type STEC cells in glass capillary tubes under continuous flow-culture conditions compared with the STEC sodC and tpx mutants. To the best of our knowledge, this is the first mutational study to show the contribution of sodC and tpx gene products to the formation of an E. coli O157:H7 biofilm. These results also suggest that these biofilms are physiologically heterogeneous and that oxidative stress defenses in both the exponential and stationary growth stages play important roles in the formation of STEC biofilms.

Characterization of the OxyR regulon of Neisseria gonorrhoeae

OxyR regulates the expression of the majority of H(2)O(2) responses in Gram-negative organisms. In a previous study we reported the OxyR-dependent derepression of catalase expression in the human pathogen Neisseria gonorrhoeae. In the present study we used microarray expression profiling of N. gonorrhoeae wild-type strain 1291 and an oxyR mutant strain to define the OxyR regulon. In addition to katA (encoding catalase), only one other locus displayed a greater than two-fold difference in expression in the wild type : oxyR comparison. This locus encodes an operon of two genes, a putative peroxiredoxin/glutaredoxin (Prx) and a putative glutathione oxidoreductase (Gor). Mutant strains were constructed in which each of these genes was inactivated. A previous biochemical study in Neisseria meningitidis had confirmed function of the glutaredoxin/peroxiredoxin. Assay of the wild-type 1291 cell free extract confirmed Gor activity, which was lost in the gor mutant strain. Phenotypic analysis of the prx mutant strain in H(2)O(2) killing assays revealed increased resistance, presumably due to upregulation of alternative defence mechanisms. The oxyR, prx and gor mutant strains were deficient in biofilm formation, and the oxyR and prx strains had decreased survival in cervical epithelial cells, indicating a key role for the OxyR regulon in these processes.

Cofacial Heme Binding is Linked to Dimerization by a Bacterial Heme Transport Protein

Campylobacter jejuni is a leading bacterial cause of food-borne illness in the developed world. Like most pathogens, C. jejuni requires iron that must be acquired from the host environment. Although the iron preference of the food-borne pathogen C. jejuni is not established, this organism possesses heme transport systems to acquire iron. ChaN is an iron-regulated lipoprotein from C. jejuni proposed to be associated with ChaR, an outer-membrane receptor. Mutation of PhuW, a ChaN orthologue in Pseudomonas aeruginosa, compromises growth on heme as a sole iron source. The crystal structure of ChaN, determined to 1.9 A resolution reveals that ChaN is comprised of a large parallel beta-sheet with flanking alpha-helices and a smaller domain consisting of alpha-helices. Unexpectedly, two cofacial heme groups ( approximately 3.5 A apart with an inter-iron distance of 4.4 A) bind in a pocket formed by a dimer of ChaN monomers. Each heme iron is coordinated by a single tyrosine from one monomer, and the propionate groups are hydrogen bonded by a histidine and a lysine from the other monomer. Sequence analyses reveal that these residues are conserved among ChaN homologues from diverse bacterial origins. Electronic absorption and electron paramagnetic resonance (EPR) spectroscopy are consistent with heme binding through tyrosine coordination by ChaN in solution yielding a high-spin heme iron structure in a pH-dependent equilibrium with a low-spin species. Analytical ultracentrifugation demonstrates that apo-ChaN is predominantly monomeric and that dimerization occurs with heme binding such that the stability constant for dimer formation increases by 60-fold.

Iron-withholding strategy in innate immunity

The knowledge of how organisms fight infections has largely been built upon the ability of host innate immune molecules to recognize microbial determinants. Although of overwhelming importance, pathogen recognition is but only one of the facets of innate immunity. A primitive yet effective antimicrobial mechanism which operates by depriving microbial organisms of their nutrients has been brought into the forefront of innate immunity once again. Such a tactic is commonly referred to as the iron-withholding strategy of innate immunity. In this review, we introduce various vertebrate iron-binding proteins and their invertebrate homologues, so as to impress upon readers an obscured arm of innate immune defense. An excellent comprehension of the mechanics of innate immunity paves the way for the possibility that novel antimicrobial therapeutics may emerge one day to overcome the prevalent antibiotic resistance in bacteria.