Identification of a new genePA5017involved in flagella-mediated motility, chemotaxis and biofilm formation inPseudomonas aeruginosa

The dynamics of biofilm development and dispersal should be taken into account when quantifying biofilm via the crystal violet microtiter plate assay

The crystal violet microtiter plate biofilm assay is often used to compare the amount of biofilm formed by a mutant versus wild-type or a compound-treated biofilm versus the non-treatment control. In many of these studies the amount of biofilm is assessed only at one single time point. However, if the dynamics of biofilm development of the mutant (or compound-treated biofilm) is different than that of the wild-type (or non-treatment control), then biofilm quantification at a single time point may give misleading results. To overcome this shortcoming of the common biofilm quantification technique, we recommend to use a serial dilution-based crystal violet microtiter plate biofilm assay for easy assessment of the dynamics of biofilm development and dispersal. We demonstrate that the dilution-resolved crystal violet assay displays the dynamics of Pseudomonas aeruginosa biofilm development and dispersal as efficient as a time-resolved crystal violet assay. In addition, focusing on mutants of different parts of the c-di-GMP signaling system in P. aeruginosa, we provide an example illustrating the need to assess biofilm dynamics instead of quantifying biofilm biomass at a single time point.

Effects of the quorum sensing related luxS gene and lsr operon on Klebsiella michiganensis resisting copper stress

Industrial wastewater is a major environmental concern due to its high copper content, which poses significant toxicity to microbial life. Autoinducer-2 (AI-2) can participate in the inter- and intra-species communication and regulate the physiological functions of different bacterial species by producing AI-2 signal molecules. However, there are few research reports on the luxS gene and lsr operon functions for AI-2 in bacteria with a certain tolerance to copper. This study delves into the potential of quorum sensing mechanisms, particularly the AI-2 system, for enhancing microbial resistance to copper toxicity in Klebsiella michiganensis (KM). We detail the critical roles of the luxS gene in AI-2 synthesis and the lsr operon in AI-2 uptake, demonstrating their collective impact on enhancing copper resistance. Our findings show that mutations in the lsr operon, alongside the knockout of the luxS gene in KM strain (KMΔluxSΔlsr), significantly impair the strain's motility (p < 0.0001) and biofilm formation (p < 0.01), underscoring the operon's role in AI-2 transport. These genetic insights are pivotal for developing bioremediation strategies aimed at mitigating copper pollution in wastewater. By elucidating the mechanisms through which KM modulates copper resistance, this study highlights the broader ecological significance of leveraging microbial quorum sensing pathways for sustainable wastewater management.

Citric Acid in Rice Root Exudates Enhanced the Colonization and Plant Growth-Promoting Ability of Bacillus altitudinis LZP02

Exploration of the underlying mechanisms of plant-microbe interactions is very important. In the present study, citric acid in the root exudates of rice significantly enhanced the colonization of Bacillus altitudinis LZP02 in the rhizosphere. According to the results of transcriptome and reverse transcription-quantitative PCR or analyses, citric acid increased the expression of several genes involved in bacterial chemotaxis and biofilm formation in B. altitudinis LZP02. In addition, citric acid also increased the expression of several genes associated with S-adenosylmethionine biosynthesis and metabolism. Interestingly, the secretion of citric acid by rice roots could be increased by inoculation with B. altitudinis LZP02. The result indicated that citric acid might be a vital signal in the interaction between rice and B. altitudinis LZP02. Further verification showed that citric acid enhanced the plant growth-promoting ability of B. altitudinis LZP02. IMPORTANCE In a previous study, the mechanism by which citric acid in rice root exudates enhanced the colonization of Bacillus altitudinis LZP02 was discovered. The present study verified that citric acid increased the recruitment and rice growth-promoting ability of B. altitudinis LZP02. These findings serve as an interesting case for explaining the underlying mechanisms of plant-microbe interactions. Henceforth, citric acid and B. altitudinis LZP02 could be exploited for the development of sustainable agronomy.

Pseudomonas aeruginosa-accelerated corrosion of Mo-bearing low-alloy steel through molybdenum-mediating chemotaxis and motility

In this work, we found that the microbiologically influenced corrosion of Pseudomonas aeruginosa was mediated by Mo in low-alloy steel. Through immersion experiments, we found that the corrosion rate of low-alloy steel was not decreased with the addition of 1.0 wt% Mo. However, in the presence of P. aeruginosa, the corrosion rate of the 1.0 wt% Mo steel was accelerated, resulting in the development of pits. Confocal laser scanning microscopy images revealed that more biofilm cells adhered on the 1.0 wt% Mo steel surface. The chemotactic behavior and swimming ability of the bacteria were the main reason for the greater biofilm cell adhesion in the presence of Mo. Using an RNA-seq assay, we verified that both chemotaxis and motility together affected the adhesion of biofilm, and their related genes were affected by Mo.

Phylogenetic Analysis with Prediction of Cofactor or Ligand Binding for Pseudomonas aeruginosa PAS and Cache Domains

PAS domains are omnipresent building blocks of multidomain proteins in all domains of life. Bacteria possess a variety of PAS domains in intracellular proteins and the related Cache domains in periplasmic or extracellular proteins. PAS and Cache domains are predominant in sensory systems, often carry cofactors or bind ligands, and serve as dimerization domains in protein association. To aid our understanding of the wide distribution of these domains, we analyzed the proteome of the opportunistic human pathogen Pseudomonas aeruginosa PAO1 in silico. The ability of this bacterium to survive under different environmental conditions, to switch between planktonic and sessile/biofilm lifestyle, or to evade stresses, notably involves c-di-GMP regulatory proteins or depends on sensory pathways involving multidomain proteins that possess PAS or Cache domains. Maximum likelihood phylogeny was used to group PAS and Cache domains on the basis of amino acid sequence. Conservation of cofactor- or ligand-coordinating amino acids aided by structure-based comparison was used to inform function. The resulting classification presented here includes PAS domains that are candidate binders of carboxylic acids, amino acids, fatty acids, flavin adenine dinucleotide (FAD), 4-hydroxycinnamic acid, and heme. These predictions are put in context to previously described phenotypic data, often generated from deletion mutants. The analysis predicts novel functions for sensory proteins and sheds light on functional diversification in a large set of proteins with similar architecture. IMPORTANCE To adjust to a variety of life conditions, bacteria typically use multidomain proteins, where the modular structure allows functional differentiation. Proteins responding to environmental cues and regulating physiological responses are found in chemotaxis pathways that respond to a wide range of stimuli to affect movement. Environmental cues also regulate intracellular levels of cyclic-di-GMP, a universal bacterial secondary messenger that is a key determinant of bacterial lifestyle and virulence. We study Pseudomonas aeruginosa, an organism known to colonize a broad range of environments that can switch lifestyle between the sessile biofilm and the planktonic swimming form. We have investigated the PAS and Cache domains, of which we identified 101 in 70 Pseudomonas aeruginosa PAO1 proteins, and have grouped these by phylogeny with domains of known structure. The resulting data set integrates sequence analysis and structure prediction to infer ligand or cofactor binding. With this data set, functional predictions for PAS and Cache domain-containing proteins are made.

Differential impact on motility and biofilm dispersal of closely related phosphodiesterases in Pseudomonas aeruginosa

In Pseudomonas aeruginosa, the transition between planktonic and biofilm lifestyles is modulated by the intracellular secondary messenger cyclic dimeric-GMP (c-di-GMP) in response to environmental conditions. Here, we used gene deletions to investigate how the environmental stimulus nitric oxide (NO) is linked to biofilm dispersal, focusing on biofilm dispersal phenotype from proteins containing putative c-di-GMP turnover and Per-Arnt-Sim (PAS) sensory domains. We document opposed physiological roles for the genes ΔrbdA and Δpa2072 that encode proteins with identical domain structure: while ΔrbdA showed elevated c-di-GMP levels, restricted motility and promoted biofilm formation, c-di-GMP levels were decreased in Δpa2072, and biofilm formation was inhibited, compared to wild type. A second pair of genes, ΔfimX and ΔdipA, were selected on the basis of predicted impaired c-di-GMP turnover function: ΔfimX showed increased, ΔdipA decreased NO induced biofilm dispersal, and the genes effected different types of motility, with reduced twitching for ΔfimX and reduced swimming for ΔdipA. For all four deletion mutants we find that NO-induced biomass reduction correlates with increased NO-driven swarming, underlining a significant role for this motility in biofilm dispersal. Hence P. aeruginosa is able to differentiate c-di-GMP output using structurally highly related proteins that can contain degenerate c-di-GMP turnover domains.

Pulmonary Pathogens Adapt to Immune Signaling Metabolites in the Airway

A limited number of pulmonary pathogens are able to evade normal mucosal defenses to establish acute infection and then adapt to cause chronic pneumonias. Pathogens, such as Pseudomonas aeruginosa or Staphylococcus aureus, are typically associated with infection in patients with underlying pulmonary disease or damage, such as cystic fibrosis (CF) or chronic obstructive pulmonary disease (COPD). To establish infection, bacteria express a well-defined set of so-called virulence factors that facilitate colonization and activate an immune response, gene products that have been identified in murine models. Less well-understood are the adaptive changes that occur over time in vivo, enabling the organisms to evade innate and adaptive immune clearance mechanisms. These colonizers proliferate, generating a population sufficient to provide selection for mutants, such as small colony variants and mucoid variants, that are optimized for long term infection. Such host-adapted strains have evolved in response to selective pressure such as antibiotics and the recruitment of phagocytes at sites of infection and their release of signaling metabolites (e.g., succinate). These metabolites can potentially function as substrates for bacterial growth and but also generate oxidant stress. Whole genome sequencing and quantified expression of selected genes have helped to explain how P. aeruginosa and S. aureus adapt to the presence of these metabolites over the course of in vivo infection. The serial isolation of clonally related strains from patients with cystic fibrosis has provided the opportunity to identify bacterial metabolic pathways that are altered under this immune pressure, such as the anti-oxidant glyoxylate and pentose phosphate pathways, routes contributing to the generation of biofilms. These metabolic pathways and biofilm itself enable the organisms to dissipate oxidant stress, while providing protection from phagocytosis. Stimulation of host immune signaling metabolites by these pathogens drives bacterial adaptation and promotes their persistence in the airways. The inherent metabolic flexibility of P. aeruginosa and S. aureus is a major factor in their success as pulmonary pathogens.

PA5001 gene involves in swimming motility and biofilm formation in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a nosocomial human pathogen causing infections in immunocompromised patients. To explore new genes involved in P. aeruginosa swimming motility, Mu transposon mutagenesis library was screened for isolates with altered swimming motility. Eleven nonmobile mutants were identified. Sequence analysis shows the nonmobile phenotype of one isolate was attributed to the inactivation of PA5001 gene. PA5001 knockout mutant based on the PAK lab strain also displayed comparable phenotypes suggesting the universal gene function regardless of strain. Exotic PA5001 gene fragment provided on expressing plasmid was capable of storing nonmobile phenotype of PA5001 mutant, suggesting the functional involvement of PA5001 gene on bacterial swimming. Impact of PA5001 inactivation on biofilm formation was examined, as adhesion and interaction during biofilm formation is highly dependent of bacterial mobility. The result shows that normal architecture of biofilm was disrupted in the mutant. Complementing by exotic PA5001 gene fragment resulted in the restoration of biofilm phenotype. Our results provide evidences suggesting the functional participation of PA5001 gene in bacterial mobility and biofilm formation. The critical function by PA5001 in bacterial motility and biofilm might serve as hint for the novel target for the treatment of chronic infections caused by P. aeruginosa.

High levels of cAMP inhibit Pseudomonas aeruginosa biofilm formation through reduction of the c-di-GMP content

The human pathogen Pseudomonas aeruginosa can cause both acute infections and chronic biofilm-based infections. Expression of acute virulence factors is positively regulated by cAMP, whereas biofilm formation is positively regulated by c-di-GMP. We provide evidence that increased levels of cAMP, caused by either a lack of degradation or increased production, inhibit P. aeruginosa biofilm formation. cAMP-mediated inhibition of P. aeruginosa biofilm formation required Vfr, and involved a reduction of the level of c-di-GMP, as well as reduced production of biofilm matrix components. A mutant screen and characterization of defined knockout mutants suggested that a subset of c-di-GMP-degrading phosphodiesterases is involved in cAMP-Vfr-mediated biofilm inhibition in P. aeruginosa.

Multiple Environmental Factors Influence the Importance of the Phosphodiesterase DipA upon Pseudomonas aeruginosa Swarming

Pseudomonas aeruginosa exhibits flagellum-mediated swimming in liquid and swarming on hydrated surfaces under diverse nutrient conditions. Prior studies have implicated a phosphodiesterase, DipA, in regulating these flagellum-mediated motilities, but collectively, the necessity for DipA was unclear. In this study, we find that the medium composition conditionally constrains the influence of DipA on flagellar motility. We show that DipA exhibits more influence on minimal medium supplemented with glutamate or glucose, where flagellar motility was negated for the dipA mutant. Conversely, a dipA-deficient mutant exhibits flagellar motility when growing with LB Lennox broth and minimal medium supplemented with Casamino Acids. Swarming under these rich medium conditions occurs under elevated levels of c-di-GMP. We also demonstrate that the influence of DipA upon swimming often differs from that upon swarming, and we conclude that a direct comparison of the motility phenotypes is generally valid only when characterizing motility assay results from the same medium composition. Our results are consistent with the explanation that DipA is one of several phosphodiesterases responding to the nutrient environment sensed by P. aeruginosa On minimal medium with glutamate or glucose, DipA is dominant; however, on rich medium, the necessity of DipA is fully negated.IMPORTANCE Motile and ubiquitous bacteria such as Pseudomonas aeruginosa can quickly colonize surfaces and form biofilms in numerous environments such as water distribution systems, soil, and the human lung. To effectively disrupt bacterial colonization, it is imperative to understand how bacteria regulate motility in these different growth environments. Here, we show that the phosphodiesterase DipA is not required for flagellar motility under all nutrient conditions. Thus, the maintenance of intracellular c-di-GMP levels to promote flagellar motility or biofilm development must be conditionally regulated by differing phosphodiesterases in variation with select nutrient cues.

In vitro effects of anthocyanidins on sinonasal epithelial nitric oxide production and bacterial physiology

BACKGROUND

T2R bitter taste receptors play a crucial role in sinonasal innate immunity by upregulating mucociliary clearance and nitric oxide (NO) production in response to bitter gram-negative quorum-sensing molecules in the airway surface liquid. Previous studies showed that phytochemical flavonoid metabolites, known as anthocyanidins, taste bitter and have antibacterial effects. Our objectives were to examine the effects of anthocyanidins on NO production by human sinonasal epithelial cells and ciliary beat frequency, and their impact on common sinonasal pathogens Pseudomonas aeruginosa and Staphylococcus aureus.

METHODS

Ciliary beat frequency and NO production were measured by using digital imaging of differentiated air-liquid interface cultures prepared from primary human cells isolated from residual surgical material. Plate-based assays were used to determine the effects of anthocyanidins on bacterial swimming and swarming motility. Biofilm formation and planktonic growth were also assessed.

RESULTS

Anthocyanidin compounds triggered epithelial cells to produce NO but not through T2R receptors. However, anthocyanidins did not impact ciliary beat frequency. Furthermore, they did not reduce biofilm formation or planktonic growth of P. aeruginosa. In S. aureus, they did not reduce planktonic growth, and only one compound had minimal antibiofilm effects. The anthocyanidin delphinidin and anthocyanin keracyanin were found to promote bacterial swimming, whereas anthocyanidin cyanidin and flavonoid myricetin did not. No compounds that were tested inhibited bacterial swarming.

CONCLUSION

Results of this study indicated that, although anthocyanidins may elicited an innate immune NO response from human cells, they do not cause an increase in ciliary beating and they may also cause a pathogenicity-enhancing effect in P. aeruginosa. Additional studies are necessary to understand how this would affect the use of anthocyanidins as therapeutics. This study emphasized the usefulness of in vitro screening of candidate compounds against multiple parameters of both epithelial and bacterial physiologies to prioritize candidates for in vivo therapeutic testing.

c-di-GMP and its Effects on Biofilm Formation and Dispersion: a Pseudomonas Aeruginosa Review

Since its initial discovery as an allosteric factor regulating cellulose biosynthesis in Gluconacetobacter xylinus, the list of functional outputs regulated by c-di-GMP has grown. We have focused this article on one of these c-di-GMP-regulated processes, namely, biofilm formation in the organism Pseudomonas aeruginosa. The majority of diguanylate cyclases and phosphodiesterases encoded in the P. aeruginosa genome still remain uncharacterized; thus, there is still a great deal to be learned about the link between c-di-GMP and biofilm formation in this microbe. In particular, while a number of c-di-GMP metabolizing enzymes have been identified that participate in reversible and irreversible attachment and biofilm maturation, there is a still a significant knowledge gap regarding the c-di-GMP output systems in this organism. Even for the well-characterized Pel system, where c-di-GMP-mediated transcriptional regulation is now well documented, how binding of c-di-GMP by PelD stimulates Pel production is not understood in any detail. Similarly, c-di-GMP-mediated control of swimming, swarming and twitching also remains to be elucidated. Thus, despite terrific advances in our understanding of P. aeruginosa biofilm formation and the role of c-di-GMP in this process since the last version of this book (indeed there was no chapter on c-di-GMP!) there is still much to learn.

Gentamicin dosing strategy in patients with end-stage renal disease receiving haemodialysis: evaluation using a semi-mechanistic pharmacokinetic/pharmacodynamic model

OBJECTIVES

Gentamicin is widely used in end-stage renal disease (ESRD) patients for the treatment of infections. The goal of this study was to find the most reasonable dosing regimen for gentamicin in ESRD patients receiving haemodialysis.

METHODS

The in vitro antimicrobial activity of gentamicin was evaluated by static and dynamic time-kill experiments against three bacterial strains of MSSA, MRSA and Pseudomonas aeruginosa. A semi-mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model was established afterwards, allowing the characterization of the antibacterial effect of gentamicin in the human body. The model was utilized to assess dosing regimens of gentamicin in ESRD patients receiving haemodialysis, taking both efficacy and safety into account.

RESULTS

The PK/PD model was capable of describing the bacterial response to gentamicin exposure in all three strains. Simulation based on the PK/PD model showed that pre-dialysis and post-dialysis dosing would bring comparable benefit to the ESRD patient regardless of whether the PK/PD target (fCmax/MIC >8-fold) was achieved, while the post-dialysis dosing resulted in a significantly lower trough concentration. The result of simulated dose fractionation demonstrated that both fCmax/MIC and fAUC(0-24)/MIC are strong predictors of drug effectiveness, but the PK/PD model would provide a more precise prediction of antibacterial activity as well as valuable information on dose selection in ESRD patients receiving haemodialysis.

CONCLUSIONS

Our study supports the original FDA label with regard to the dosing regimen of gentamicin in ESRD patients, which offers adequate clinical benefit as well as an acceptable safety profile.

A GFP promoter fusion library for the study of Salmonella biofilm formation and the mode of action of biofilm inhibitors

Salmonella, an important foodborne pathogen, forms biofilms in many different environments. The composition of these biofilms differs depending on the growth conditions, and their development is highly coordinated in time. To develop efficient treatments, it is therefore essential that biofilm formation and its inhibition be understood in different environments and in a time-dependent manner. Many currently used techniques, such as transcriptomics or proteomics, are still expensive and thus limited in their application. Therefore, a GFP-promoter fusion library with 79 important Salmonella biofilm genes was developed (covering among other things matrix production, fimbriae and flagella synthesis, and c-di-GMP regulation). This library is a fast, inexpensive, and easy-to-use tool, and can therefore be conducted in different experimental setups in a time-dependent manner. In this paper, four possible applications are highlighted to illustrate and validate the use of this reporter fusion library.

c-di-GMP heterogeneity is generated by the chemotaxis machinery to regulate flagellar motility

Individual cell heterogeneity is commonly observed within populations, although its molecular basis is largely unknown. Previously, using FRET-based microscopy, we observed heterogeneity in cellular c-di-GMP levels. In this study, we show that c-di-GMP heterogeneity in Pseudomonas aeruginosa is promoted by a specific phosphodiesterase partitioned after cell division. We found that subcellular localization and reduction of c-di-GMP levels by this phosphodiesterase is dependent on the histidine kinase component of the chemotaxis machinery, CheA, and its phosphorylation state. Therefore, individual cell heterogeneity in c-di-GMP concentrations is regulated by the activity and the asymmetrical inheritance of the chemotaxis organelle after cell division. c-di-GMP heterogeneity results in a diversity of motility behaviors. The generation of diverse intracellular concentrations of c-di-GMP by asymmetric partitioning is likely important to the success and survival of bacterial populations within the environment by allowing a variety of motility behaviors.

DOI:http://dx.doi.org/10.7554/eLife.01402.001

Bacterial populations have traditionally been assumed to be made up of identical cells. However, while the bacteria within a population may be genetically identical, individual cells have different growth rates, metabolisms and motilities, among other things. This ‘phenotypic heterogeneity’ has been observed in many different species of bacteria, and in some cases it can be attributed to changes in the concentration of molecules called second messengers that help to relay signals from the external environment to targets within the cell.

It can be challenging to monitor changes in the concentration of specific molecules inside cells, but researchers recently developed a form of microscopy based on FRET (short for Forster resonance energy transfer) that can measure the levels of a second messenger molecule called cyclic di-guanylate (c-di-GMP) inside individual cells. This technique was used to study P. aeruginosa, a bacterium that has a single corkscrew-shaped propeller that enables it to swim through liquid. P. aeruginosa divides to form two daughter cells—one with a propeller and one without.

Although the daughter cell that does not have a propeller quickly grows one, FRET-based microscopy revealed that the daughter cell with a propeller had less c-di-GMP than the daughter without a propeller, but the reasons underlying this difference and its effects on bacterial behavior were not clear.

Now Kulasekara et al. show that the cell that inherits the propeller contains an enzyme that degrades c-di-GMP, and that the low levels of this second messenger molecule—caused by the enzyme being concentrated near the base of the propeller, and the presence of a protein (CheA) that enables the bacteria to swim towards sources of nutrients—result in faster swimming speeds and increased responsiveness to nutrients. In other words, although the two daughter cells are genetically identical, they behave quite differently because of the different levels of this second messenger molecule.

The existence of heterogeneity within a bacterial population likely leads to increased success and survival within changing diverse environments, and this work sets the stage for similar investigations into what establishes heterogeneity in other bacterial populations.

DOI:http://dx.doi.org/10.7554/eLife.01402.002

The phosphodiesterase DipA (PA5017) is essential for Pseudomonas aeruginosa biofilm dispersion

Although little is known regarding the mechanism of biofilm dispersion, it is becoming clear that this process coincides with alteration of cyclic di-GMP (c-di-GMP) levels. Here, we demonstrate that dispersion by Pseudomonas aeruginosa in response to sudden changes in nutrient concentrations resulted in increased phosphodiesterase activity and reduction of c-di-GMP levels compared to biofilm and planktonic cells. By screening mutants inactivated in genes encoding EAL domains for nutrient-induced dispersion, we identified in addition to the previously reported ΔrbdA mutant a second mutant, the ΔdipA strain (PA5017 [dispersion-induced phosphodiesterase A]), to be dispersion deficient in response to glutamate, nitric oxide, ammonium chloride, and mercury chloride. Using biochemical and in vivo studies, we show that DipA associates with the membrane and exhibits phosphodiesterase activity but no detectable diguanylate cyclase activity. Consistent with these data, a ΔdipA mutant exhibited reduced swarming motility, increased initial attachment, and polysaccharide production but only somewhat increased biofilm formation and c-di-GMP levels. DipA harbors an N-terminal GAF (cGMP-specific phosphodiesterases, adenylyl cyclases, and FhlA) domain and two EAL motifs within or near the C-terminal EAL domain. Mutational analyses of the two EAL motifs of DipA suggest that both are important for the observed phosphodiesterase activity and dispersion, while the GAF domain modulated DipA function both in vivo and in vitro without being required for phosphodiesterase activity. Dispersion was found to require protein synthesis and resulted in increased dipA expression and reduction of c-di-GMP levels. We propose a role of DipA in enabling dispersion in P. aeruginosa biofilms.

A histidine-kinase cheA gene of Pseudomonas pseudoalcaligens KF707 not only has a key role in chemotaxis but also affects biofilm formation and cell metabolism

A histidine-kinase cheA gene in Pseudomonas pseudoalcaligenes KF707 plays a central role in the regulation of metabolic responses as well as in chemotaxis. Non-chemotactic mutants harboring insertions into the cheA gene were screened for their ability to form biofilms in the Calgary biofilm device. Notably, ≥95% decrease in the number of cells attached to the polystyrene surface was observed in cheA mutants compared to the KF707 wild-type biofilm phenotype. The ability to form mature biofilms was restored to wild-type levels, providing functional copies of the KF707 cheA gene to the mutants. In addition, phenotype micro-arrays and proteomic analyses revealed that several basic metabolic activities and a few periplasmic binding proteins of cheA mutant cells differed compared to those of wild-type cells. These results are interpreted as evidence of a strong integration between chemotactic and metabolic pathways in the process of biofilm development by P. pseudoalcaligenes KF707.

Acid-stress-induced changes in enterohaemorrhagic Escherichia coli O157 : H7 virulence

Enterohaemorrhagic Escherichia coli (EHEC) O157 : H7 is naturally exposed to a wide variety of stresses including gastric acid shock, and yet little is known about how this stress influences virulence. This study investigated the impact of acid stress on several critical virulence properties including survival, host adhesion, Shiga toxin production, motility and induction of host-cell apoptosis. Several acid-stress protocols with relevance for gastric passage as well as external environmental exposure were included. Acute acid stress at pH 3 preceded by acid adaptation at pH 5 significantly enhanced the adhesion of surviving organisms to epithelial cells and bacterial induction of host-cell apoptosis. Motility was also significantly increased after acute acid stress. Interestingly, neither secreted nor periplasmic levels of Shiga toxin were affected by acid shock. Pretreatment of bacteria with erythromycin eliminated the acid-induced adhesion enhancement, suggesting that de novo protein synthesis was required for the enhanced adhesion of acid-shocked organisms. DNA microarray was used to analyse the transcriptome of an EHEC O157 : H7 strain exposed to three different acid-stress treatments. Expression profiles of acid-stressed EHEC revealed significant changes in virulence factors associated with adhesion, motility and type III secretion. These results document profound changes in the virulence properties of EHEC O157 : H7 after acid stress, provide a comprehensive genetic analysis to substantiate these changes and suggest strategies that this pathogen may use during gastric passage and colonization in the human gastrointestinal tract.