Evidence that putrescine acts as an extracellular signal required for swarming in Proteus mirabilis

Effect of Quorum Sensing by Staphylococcus epidermidis on the Attraction Response of Female Adult Yellow Fever Mosquitoes, Aedes aegypti aegypti (Linnaeus) (Diptera: Culicidae), to a Blood-Feeding Source

Aedes aegypti, the principal vector of yellow fever and dengue fever, is responsible for more than 30,000 deaths annually. Compounds such as carbon dioxide, amino acids, fatty acids and other volatile organic compounds (VOCs) have been widely studied for their role in attracting Ae. aegypti to hosts. Many VOCs from humans are produced by associated skin microbiota. Staphyloccocus epidermidis, although not the most abundant bacteria according to surveys of relative 16S ribosomal RNA abundance, commonly occurs on human skin. Bacteria demonstrate population level decision-making through quorum sensing. Many quorum sensing molecules, such as indole, volatilize and become part of the host odor plum. To date, no one has directly demonstrated the link between quorum sensing (i.e., decision-making) by bacteria associated with a host as a factor regulating arthropod vector attraction. This study examined this specific question with regards to S. epidermidis and Ae. aegypti. Pairwise tests were conducted to examine the response of female Ae. aegypti to combinations of tryptic soy broth (TSB) and S. epidermidis wildtype and agr- strains. The agr gene expresses an accessory gene regulator for quorum sensing; therefore, removing this gene inhibits quorum sensing of the bacteria. Differential attractiveness of mosquitoes to the wildtype and agr- strains was observed. Both wildtype and the agr- strain of S. epidermidis with TSB were marginally more attractive to Ae. aegypti than the TSB alone. Most interestingly, the blood-feeder treated with wildtype S. epidermidis/TSB attracted 74% of Ae. aegypti compared to the agr- strain of S. epidermidis/TSB (P ≤ 0.0001). This study is the first to suggest a role for interkingdom communication between host symbiotic bacteria and mosquitoes. This may have implications for mosquito decision-making with regards to host detection, location and acceptance. We speculate that mosquitoes "eavesdrop" on the chemical discussions occurring between host-associated microbes to determine suitability for blood feeding. We believe these data suggest that manipulating quorum sensing by bacteria could serve as a novel approach for reducing mosquito attraction to hosts, or possibly enhancing the trapping of adults at favored oviposition sites.

Omics on bioleaching: current and future impacts

Bioleaching corresponds to the microbial-catalyzed process of conversion of insoluble metals into soluble forms. As an applied biotechnology globally used, it represents an extremely interesting field of research where omics techniques can be applied in terms of knowledge development, but moreover in terms of process design, control, and optimization. In this mini-review, the current state of genomics, proteomics, and metabolomics of bioleaching and the major impacts of these analytical methods at industrial scale are highlighted. In summary, genomics has been essential in the determination of the biodiversity of leaching processes and for development of conceptual and functional metabolic models. Proteomic impacts are mostly related to microbe-mineral interaction analysis, including copper resistance and biofilm formation. Early steps of metabolomics in the field of bioleaching have shown a significant potential for the use of metabolites as industrial biomarkers. Development directions are given in order to enhance the future impacts of the omics in biohydrometallurgy.

Molecular and chemical dialogues in bacteria-protozoa interactions

Protozoan predation of bacteria can significantly affect soil microbial community composition and ecosystem functioning. Bacteria possess diverse defense strategies to resist or evade protozoan predation. For soil-dwelling Pseudomonas species, several secondary metabolites were proposed to provide protection against different protozoan genera. By combining whole-genome transcriptome analyses with (live) imaging mass spectrometry (IMS), we observed multiple changes in the molecular and chemical dialogues between Pseudomonas fluorescens and the protist Naegleria americana. Lipopeptide (LP) biosynthesis was induced in Pseudomonas upon protozoan grazing and LP accumulation transitioned from homogeneous distributions across bacterial colonies to site-specific accumulation at the bacteria-protist interface. Also putrescine biosynthesis was upregulated in P. fluorescens upon predation. We demonstrated that putrescine induces protozoan trophozoite encystment and adversely affects cyst viability. This multifaceted study provides new insights in common and strain-specific responses in bacteria-protozoa interactions, including responses that contribute to bacterial survival in highly competitive soil and rhizosphere environments.

Regulation of the Min Cell Division Inhibition Complex by the Rcs Phosphorelay in Proteus mirabilis

A key regulator of swarming in Proteus mirabilis is the Rcs phosphorelay, which represses flhDC, encoding the master flagellar regulator FlhD4C2. Mutants in rcsB, the response regulator in the Rcs phosphorelay, hyperswarm on solid agar and differentiate into swarmer cells in liquid, demonstrating that this system also influences the expression of genes central to differentiation. To gain a further understanding of RcsB-regulated genes involved in swarmer cell differentiation, transcriptome sequencing (RNA-Seq) was used to examine the RcsB regulon. Among the 133 genes identified, minC and minD, encoding cell division inhibitors, were identified as RcsB-activated genes. A third gene, minE, was shown to be part of an operon with minCD. To examine minCDE regulation, the min promoter was identified by 5' rapid amplification of cDNA ends (5'-RACE), and both transcriptional lacZ fusions and quantitative real-time reverse transcriptase (qRT) PCR were used to confirm that the minCDE operon was RcsB activated. Purified RcsB was capable of directly binding the minC promoter region. To determine the role of RcsB-mediated activation of minCDE in swarmer cell differentiation, a polar minC mutation was constructed. This mutant formed minicells during growth in liquid, produced shortened swarmer cells during differentiation, and exhibited decreased swarming motility.

IMPORTANCE

This work describes the regulation and role of the MinCDE cell division system in P. mirabilis swarming and swarmer cell elongation. Prior to this study, the mechanisms that inhibit cell division and allow swarmer cell elongation were unknown. In addition, this work outlines for the first time the RcsB regulon in P. mirabilis. Taken together, the data presented in this study begin to address how P. mirabilis elongates upon contact with a solid surface.

Transcriptional analysis of the MrpJ network: modulation of diverse virulence-associated genes and direct regulation of mrp fimbrial and flhDC flagellar operons in Proteus mirabilis

The enteric bacterium Proteus mirabilis is associated with a significant number of catheter-associated urinary tract infections (UTIs). Strict regulation of the antagonistic processes of adhesion and motility, mediated by fimbriae and flagella, respectively, is essential for disease progression. Previously, the transcriptional regulator MrpJ, which is encoded by the mrp fimbrial operon, has been shown to repress both swimming and swarming motility. Here we show that MrpJ affects an array of cellular processes beyond adherence and motility. Microarray analysis found that expression of mrpJ mimicking levels observed during UTIs leads to differential expression of 217 genes related to, among other functions, bacterial virulence, type VI secretion, and metabolism. We probed the molecular mechanism of transcriptional regulation by MrpJ using transcriptional reporters and chromatin immunoprecipitation (ChIP). Binding of MrpJ to two virulence-associated target gene promoters, the promoters of the flagellar master regulator flhDC and mrp itself, appears to be affected by the condensation state of the native chromosome, although both targets share a direct MrpJ binding site proximal to the transcriptional start. Furthermore, an mrpJ deletion mutant colonized the bladders of mice at significantly lower levels in a transurethral model of infection. Additionally, we observed that mrpJ is widely conserved in a collection of recent clinical isolates. Altogether, these findings support a role of MrpJ as a global regulator of P. mirabilis virulence.

Mutations in global regulators lead to metabolic selection during adaptation to complex environments

Adaptation to ecologically complex environments can provide insights into the evolutionary dynamics and functional constraints encountered by organisms during natural selection. Adaptation to a new environment with abundant and varied resources can be difficult to achieve by small incremental changes if many mutations are required to achieve even modest gains in fitness. Since changing complex environments are quite common in nature, we investigated how such an epistatic bottleneck can be avoided to allow rapid adaptation. We show that adaptive mutations arise repeatedly in independently evolved populations in the context of greatly increased genetic and phenotypic diversity. We go on to show that weak selection requiring substantial metabolic reprogramming can be readily achieved by mutations in the global response regulator arcA and the stress response regulator rpoS. We identified 46 unique single-nucleotide variants of arcA and 18 mutations in rpoS, nine of which resulted in stop codons or large deletions, suggesting that subtle modulations of ArcA function and knockouts of rpoS are largely responsible for the metabolic shifts leading to adaptation. These mutations allow a higher order metabolic selection that eliminates epistatic bottlenecks, which could occur when many changes would be required. Proteomic and carbohydrate analysis of adapting E. coli populations revealed an up-regulation of enzymes associated with the TCA cycle and amino acid metabolism, and an increase in the secretion of putrescine. The overall effect of adaptation across populations is to redirect and efficiently utilize uptake and catabolism of abundant amino acids. Concomitantly, there is a pronounced spread of more ecologically limited strains that results from specialization through metabolic erosion. Remarkably, the global regulators arcA and rpoS can provide a “one-step” mechanism of adaptation to a novel environment, which highlights the importance of global resource management as a powerful strategy to adaptation.

Changing environmental conditions are the norm in biology. However, understanding adaptation to complex environments presents many challenges. For example, adaptation to resource-rich environments can potentially have many successful evolutionary trajectories to increased fitness. Even in conditions of plenty, the utilization of numerous but novel resources can require multiple mutations before a benefit is accrued. We evolved two bacterial species isolated from the gut of healthy humans in two different, resource-rich media commonly used in the laboratory. We anticipated that under weak selection the population would evolve tremendous genetic diversity. Despite such a complex genetic background we were able to identify a strong degree of parallel evolution and using a combination of population proteomic and population genomic approaches we show that two global regulators, arcA and rpoS, are the principle targets of selection. Up-regulation of the different metabolic pathways that are controlled by these global regulators in combination with up-regulation of transporters that transport nutrients into the cell revealed increased use of the novel resources. Thus global regulators can provide a one-step model to shift metabolism efficiently and provide rapid a one-step reprogramming of the cell metabolic profile.

In vitro cytotoxic effects of gold nanoparticles coated with functional acyl homoserine lactone lactonase protein from Bacillus licheniformis and their antibiofilm activity against Proteus species

N-acylated homoserine lactonases are known to inhibit the signaling molecules of the biofilm-forming pathogens. In this study, gold nanoparticles were coated with N-acylated homoserine lactonase proteins (AiiA AuNPs) purified from Bacillus licheniformis. The AiiA AuNPs were characterized by UV-visible spectra, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The synthesized AiiA AuNPs were found to be spherical in shape and 10 to 30 nm in size. Treatment with AiiA protein-coated AuNPs showed maximum reduction in exopolysaccharide production, metabolic activities, and cell surface hydrophobicity and potent antibiofilm activity against multidrug-resistant Proteus species compared to treatment with AiiA protein alone. AiiA AuNPs exhibited potent antibiofilm activity at 2 to 8 μM concentrations without being harmful to the macrophages. We conclude that at a specific dose, AuNPs coated with AiiA can kill bacteria without harming the host cells, thus representing a potential template for the design of novel antibiofilm and antibacterial protein drugs to decrease bacterial colonization and to overcome the problem of drug resistance. In summary, our data suggest that the combined effect of the lactonase and the gold nanoparticles of the AiiA AuNPs has promising antibiofilm activity against biofilm-forming and multidrug-resistant Proteus species.

Arginine promotes Proteus mirabilis motility and fitness by contributing to conservation of the proton gradient and proton motive force

Swarming contributes to Proteus mirabilis pathogenicity by facilitating access to the catheterized urinary tract. We previously demonstrated that 0.1–20 mmol/L arginine promotes swarming on normally nonpermissive media and that putrescine biosynthesis is required for arginine-induced swarming. We also previously determined that arginine-induced swarming is pH dependent, indicating that the external proton concentration is critical for arginine-dependent effects on swarming. In this study, we utilized survival at pH 5 and motility as surrogates for measuring changes in the proton gradient (ΔpH) and proton motive force (μH⁺) in response to arginine. We determined that arginine primarily contributes to ΔpH (and therefore μH⁺) through the action of arginine decarboxylase (speA), independent of the role of this enzyme in putrescine biosynthesis. In addition to being required for motility, speA also contributed to fitness during infection. In conclusion, consumption of intracellular protons via arginine decarboxylase is one mechanism used by P. mirabilis to conserve ΔpH and μH⁺ for motility.

Deletion of potD, encoding a putative spermidine-binding protein, results in a complex phenotype in Legionella pneumophila

L. pneumophila is an intracellular pathogen that replicates in a membrane-bound compartment known as the Legionella-containing vacuole (LCV). We previously observed that the polyamine spermidine, produced by host cells or added exogenously, enhances the intracellular growth of L. pneumophila. To study this enhancing effect and determine whether polyamines are used as nutrients, we deleted potD from L. pneumophila strain JR32. The gene potD encodes a spermidine-binding protein that in other bacteria is essential for the function of the PotABCD polyamine transporter. Deletion of potD did not affect L. pneumophila growth in vitro in the presence or absence of spermidine and putrescine, suggesting that PotD plays a redundant or no role in polyamine uptake. However, deletion of potD resulted in a puzzlingly complex phenotype that included defects in L. pneumophila's ability to form filaments, tolerate Na(+), associate with macrophages and amoeba, recruit host vesicles to the LCV, and initiate intracellular growth. Moreover, the ΔpotD mutant was completely unable to grow in L929 cells treated with a pharmacological inhibitor of spermidine synthesis. These complex and disparate effects suggest that the L. pneumophila potD encodes either: (i) a multifunctional protein, (ii) a protein that interacts with, or regulates a, multifunctional protein, or (iii) a protein that contributes (directly or indirectly) to a regulatory network. Protein function studies with the L. pneumophila PotD protein are thus warranted.

Regulation of the swarming inhibitor disA in Proteus mirabilis

The disA gene encodes a putative amino acid decarboxylase that inhibits swarming in Proteus mirabilis. 5' rapid amplification of cDNA ends (RACE) and deletion analysis were used to identify the disA promoter. The use of a disA-lacZ fusion indicated that FlhD(4)C(2), the class I flagellar master regulator, did not have a role in disA regulation. The putative product of DisA, phenethylamine, was able to inhibit disA expression, indicating that a negative regulatory feedback loop was present. Transposon mutagenesis was used to identify regulators of disA and revealed that umoB (igaA) was a negative regulator of disA. Our data demonstrate that the regulation of disA by UmoB is mediated through the Rcs phosphorelay.

Putrescine importer PlaP contributes to swarming motility and urothelial cell invasion in Proteus mirabilis

Previously, we reported that the speA gene, encoding arginine decarboxylase, is required for swarming in the urinary tract pathogen Proteus mirabilis. In addition, this previous study suggested that putrescine may act as a cell-to-cell signaling molecule (Sturgill, G., and Rather, P. N. (2004) Mol. Microbiol. 51, 437-446). In this new study, PlaP, a putative putrescine importer, was characterized in P. mirabilis. In a wild-type background, a plaP null mutation resulted in a modest swarming defect and slightly decreased levels of intracellular putrescine. In a P. mirabilis speA mutant with greatly reduced levels of intracellular putrescine, plaP was required for the putrescine-dependent rescue of swarming motility. When a speA/plaP double mutant was grown in the presence of extracellular putrescine, the intracellular levels of putrescine were greatly reduced compared with the speA mutant alone, indicating that PlaP functioned as the primary putrescine importer. In urothelial cell invasion assays, a speA mutant exhibited a 50% reduction in invasion when compared with wild type, and this defect could be restored by putrescine in a PlaP-dependent manner. The putrescine analog Triamide-44 partially inhibited the uptake of putrescine by PlaP and decreased both putrescine stimulated swarming and urothelial cell invasion in a speA mutant.

Metabolomic study of Chilean biomining bacteria Acidithiobacillus ferrooxidans strain Wenelen and Acidithiobacillus thiooxidans strain Licanantay

In this study, we present the first metabolic profiles for two bioleaching bacteria using capillary electrophoresis coupled with mass spectrometry. The bacteria, Acidithiobacillus ferrooxidans strain Wenelen (DSM 16786) and Acidithiobacillus thiooxidans strain Licanantay (DSM 17318), were sampled at different growth phases and on different substrates: the former was grown with iron and sulfur, and the latter with sulfur and chalcopyrite. Metabolic profiles were scored from planktonic and sessile states. Spermidine was detected in intra- and extracellular samples for both strains, suggesting it has an important role in biofilm formation in the presence of solid substrate. The canonical pathway for spermidine synthesis seems absent as its upstream precursor, putrescine, was not present in samples. Glutathione, a catalytic activator of elemental sulfur, was identified as one of the most abundant metabolites in the intracellular space in A. thiooxidans strain Licanantay, confirming its participation in the sulfur oxidation pathway. Amino acid profiles varied according to the growth conditions and bioleaching species. Glutamic and aspartic acid were highly abundant in intra- and extracellular extracts. Both are constituents of the extracellular matrix, and have a probable role in cell detoxification. This novel metabolomic information validates previous knowledge from in silico metabolic reconstructions based on genomic sequences, and reveals important biomining functions such as biofilm formation, energy management and stress responses. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-012-0443-3) contains supplementary material, which is available to authorized users.

Initiation of swarming motility by Proteus mirabilis occurs in response to specific cues present in urine and requires excess L-glutamine

Proteus mirabilis, a leading cause of catheter-associated urinary tract infection (CaUTI), differentiates into swarm cells that migrate across catheter surfaces and medium solidified with 1.5% agar. While many genes and nutrient requirements involved in the swarming process have been identified, few studies have addressed the signals that promote initiation of swarming following initial contact with a surface. In this study, we show that P. mirabilis CaUTI isolates initiate swarming in response to specific nutrients and environmental cues. Thirty-three compounds, including amino acids, polyamines, fatty acids, and tricarboxylic acid (TCA) cycle intermediates, were tested for the ability to promote swarming when added to normally nonpermissive media. L-Arginine, L-glutamine, DL-histidine, malate, and DL-ornithine promoted swarming on several types of media without enhancing swimming motility or growth rate. Testing of isogenic mutants revealed that swarming in response to the cues required putrescine biosynthesis and pathways involved in amino acid metabolism. Furthermore, excess glutamine was found to be a strict requirement for swarming on normal swarm agar in addition to being a swarming cue under normally nonpermissive conditions. We thus conclude that initiation of swarming occurs in response to specific cues and that manipulating concentrations of key nutrient cues can signal whether or not a particular environment is permissive for swarming.

Merging mythology and morphology: the multifaceted lifestyle of Proteus mirabilis

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

Expression of the DisA amino acid decarboxylase from Proteus mirabilis inhibits motility and class 2 flagellar gene expression in Escherichia coli

In Proteus mirabilis, a putative phenylalanine decarboxylase (DisA) acts in a regulatory pathway to inhibit class 2 flagellar gene expression and motility. In this study, we demonstrate that DisA expression in Escherichia coli blocked motility and resulted in a 50-fold decrease in the expression of class 2 (fliA) and class 3 (fliC) flagellar genes. However, the expression of flhDC encoding the class 1 activator of the flagellar cascade was unchanged by DisA expression at both the transcriptional and translational levels. Phenethylamine, a decarboxylation product derived from phenylalanine, was able to mimic DisA overexpression and decrease both motility and class 2/3 flagellar gene expression. In addition, both DisA overexpression and phenethylamine strongly inhibited biofilm formation in E. coli. DisA overexpression and exogenous phenethylamine could also reduce motility in other enteric bacteria, but had no effect on motility in non-enteric Gram-negative bacteria. It is hypothesized that phenethylamine or a closely related compound formed by the DisA decarboxylation reaction inhibits the formation or activity of the FlhD(4)C(2) complex required for activation of class 2 genes.

Polyamines are required for virulence in Salmonella enterica serovar Typhimurium

Sensing and responding to environmental cues is a fundamental characteristic of bacterial physiology and virulence. Here we identify polyamines as novel environmental signals essential for virulence of Salmonella enterica serovar Typhimurium, a major intracellular pathogen and a model organism for studying typhoid fever. Central to its virulence are two major virulence loci Salmonella Pathogenicity Island 1 and 2 (SPI1 and SPI2). SPI1 promotes invasion of epithelial cells, whereas SPI2 enables S. Typhimurium to survive and proliferate within specialized compartments inside host cells. In this study, we show that an S. Typhimurium polyamine mutant is defective for invasion, intracellular survival, killing of the nematode Caenorhabditis elegans and systemic infection of the mouse model of typhoid fever. Virulence of the mutant could be restored by genetic complementation, and invasion and intracellular survival could, as well, be complemented by the addition of exogenous putrescine and spermidine to the bacterial cultures prior to infection. Interestingly, intracellular survival of the polyamine mutant was significantly enhanced above the wild type level by the addition of exogenous putrescine and spermidine to the bacterial cultures prior to infection, indicating that these polyamines function as an environmental signal that primes S. Typhimurium for intracellular survival. Accordingly, experiments addressed at elucidating the roles of these polyamines in infection revealed that expression of genes from both of the major virulence loci SPI1 and SPI2 responded to exogenous polyamines and was reduced in the polyamine mutant. Together our data demonstrate that putrescine and spermidine play a critical role in controlling virulence in S. Typhimurium most likely through stimulation of expression of essential virulence loci. Moreover, our data implicate these polyamines as key signals in S. Typhimurium virulence.

Proteus mirabilis interkingdom swarming signals attract blow flies

Flies transport specific bacteria with their larvae that provide a wider range of nutrients for those bacteria. Our hypothesis was that this symbiotic interaction may depend on interkingdom signaling. We obtained Proteus mirabilis from the salivary glands of the blow fly Lucilia sericata; this strain swarmed significantly and produced a strong odor that attracts blow flies. To identify the putative interkingdom signals for the bacterium and flies, we reasoned that as swarming is used by this bacterium to cover the food resource and requires bacterial signaling, the same bacterial signals used for swarming may be used to communicate with blow flies. Using transposon mutagenesis, we identified six novel genes for swarming (ureR, fis, hybG, zapB, fadE and PROSTU_03490), then, confirming our hypothesis, we discovered that fly attractants, lactic acid, phenol, NaOH, KOH and ammonia, restore swarming for cells with the swarming mutations. Hence, compounds produced by the bacterium that attract flies also are utilized for swarming. In addition, bacteria with the swarming mutation rfaL attracted fewer blow flies and reduced the number of eggs laid by the flies. Therefore, we have identified several interkingdom signals between P. mirabilis and blow flies.

Role of the Umo proteins and the Rcs phosphorelay in the swarming motility of the wild type and an O-antigen (waaL) mutant of Proteus mirabilis

Proteus mirabilis is a Gram-negative bacterium that exists as a short rod when grown in liquid medium, but during growth on surfaces it undergoes a distinct physical and biochemical change that culminates in the formation of a swarmer cell. How P. mirabilis senses a surface is not fully understood; however, the inhibition of flagellar rotation and accumulation of putrescine have been proposed to be sensory mechanisms. Our lab recently isolated a transposon insertion in waaL, encoding O-antigen ligase, that resulted in a loss of swarming but not swimming motility. The waaL mutant failed to activate flhDC, the class 1 activator of the flagellar gene cascade, when grown on solid surfaces. Swarming in the waaL mutant was restored by overexpression of flhDC in trans or by a mutation in the response regulator rcsB. To further investigate the role of the Rcs signal transduction pathway and its possible relationship with O-antigen surface sensing, mutations were made in the rcsC, rcsB, rcsF, umoB (igaA), and umoD genes in wild-type and waaL backgrounds. Comparison of the swarming phenotypes of the single and double mutants and of strains overexpressing combinations of the UmoB, UmoD, and RcsF proteins demonstrated the following: (i) there is a differential effect of RcsF and UmoB on swarming in wild-type and waaL backgrounds, (ii) RcsF inhibits UmoB activity but not UmoD activity in a wild-type background, and (iii) UmoD is able to modulate activity of the Rcs system.

Swarming motility and the control of master regulators of flagellar biosynthesis

Swarming motility is the movement of bacteria over a solid surface powered by rotating flagella. The expression of flagellar biosynthesis genes is governed by species-specific master regulator transcription factors. Mutations that reduce or enhance master regulator activity have a commensurate effect on swarming motility. Here we review what is known about the proteins that modulate swarming motility and appear to act upstream of the master flagellar regulators in diverse swarming bacteria. We hypothesize that environmental control of the master regulators is important to the swarming phenotype perhaps at the level of controlling flagellar number.

Perturbation of FliL interferes with Proteus mirabilis swarmer cell gene expression and differentiation

Proteus mirabilis is a dimorphic, motile bacterium often associated with urinary tract infections. Colonization of urinary tract surfaces is aided by swarmer cell differentiation, which is initiated by inhibition of flagellar rotation when the bacteria first contact a surface. Mutations in fliL, encoding a flagellar structural protein with an enigmatic function, result in the inappropriate production of differentiated swarmer cells, called pseudoswarmer cells, under noninducing conditions, indicating involvement of FliL in the surface sensing pathway. In the present study, we compared the fliL transcriptome with that of wild-type swarmer cells and showed that nearly all genes associated with motility (flagellar class II and III genes) and chemotaxis are repressed. In contrast, spontaneous motile revertants of fliL cells that regained motility yet produced differentiated swarmer cells under noninducing conditions transcribed flagellar class II promoters at consistent levels. Expression of umoA (a known regulator of swarmer cells), flgF, and flgI increased significantly in both swarmer and pseudoswarmer cells, as did genes in a degenerate prophage region situated immediately adjacent to the Rcs phosphorelay system. Unlike swarmer cells, pseudoswarmers displayed increased activity, rather than transcription, of the flagellar master regulatory protein, FlhD(4)C(2), and analyses of the fliL parent strain and its motile revertants showed that they result from mutations altering the C-terminal 14 amino acids of FliL. Collectively, the data suggest a functional role for the C terminus of FliL in surface sensing and implicate UmoA as part of the signal relay leading to the master flagellar regulator FlhD(4)C(2), which ultimately controls swarmer cell differentiation.

A new piece of the Shigella Pathogenicity puzzle: spermidine accumulation by silencing of the speG gene [corrected]

The genome of Shigella, a gram negative bacterium which is the causative agent of bacillary dysentery, shares strong homologies with that of its commensal ancestor, Escherichia coli. The acquisition, by lateral gene transfer, of a large plasmid carrying virulence determinants has been a crucial event in the evolution towards the pathogenic lifestyle and has been paralleled by the occurrence of mutations affecting genes, which negatively interfere with the expression of virulence factors. In this context, we have analysed to what extent the presence of the plasmid-encoded virF gene, the major activator of the Shigella regulon for invasive phenotype, has modified the transcriptional profile of E. coli. Combining results from transcriptome assays and comparative genome analyses we show that in E. coli VirF, besides being able to up-regulate several chromosomal genes, which potentially influence bacterial fitness within the host, also activates genes which have been lost by Shigella. We have focused our attention on the speG gene, which encodes spermidine acetyltransferase, an enzyme catalysing the conversion of spermidine into the physiologically inert acetylspermidine, since recent evidence stresses the involvement of polyamines in microbial pathogenesis. Through identification of diverse mutations, which prevent expression of a functional SpeG protein, we show that the speG gene has been silenced by convergent evolution and that its inactivation causes the marked increase of intracellular spermidine in all Shigella spp. This enhances the survival of Shigella under oxidative stress and allows it to better face the adverse conditions it encounters inside macrophage. This is supported by the outcome of infection assays performed in mouse peritoneal macrophages and of a competitive-infection assay on J774 macrophage cell culture. Our observations fully support the pathoadaptive nature of speG inactivation in Shigella and reveal that the accumulation of spermidine is a key determinant in the pathogenicity strategy adopted by this microrganism.

Acidic environments induce differentiation of Proteus mirabilis into swarmer morphotypes

Although swarmer morphotypes of Proteus mirabilis have long been considered to result from surfaced-induced differentiation, the present findings show that, in broth medium containing urea, acidic conditions transform some swimmer cells into elongated swarmer cells. This study has also demonstrates that P. mirabilis cells grown in acidic broth medium containing urea enhance virulence factors such as flagella production and cytotoxicity to human bladder carcinoma cell line T24, though no significant difference in urease activity under different pH conditions was found. Since there is little published data on the behavior of P. mirabilis at various hydrogen-ion concentrations, the present study may clarify aspects of cellular differentiation of P. mirabilis in patients at risk of struvite formation due to infection with urease-producing bacteria, as well as in some animals with acidic or alkaline urine.

Probiotics-induced increase of large intestinal luminal polyamine concentration may promote longevity

Many mechanisms contribute to senescence, such as telomere shortening in replicative cells, cumulative damage to DNA leading to genomic instability, and oxidative damage to molecules by reactive oxygen species (ROS). These include chronic low-grade inflammation (inflammageing), a major risk factor for ageing and age-related diseases, such as Alzheimer's disease and type II diabetes. Furthermore, the prevention of inflammageing seems to be one of the most effective approaches to increase longevity. Here, I discuss the rationale and recent evidence for probiotic-induced upregulation of intestinal luminal polyamine (PA) production in the extension of lifespan by preventing inflammageing.

Legionella pneumophila requires polyamines for optimal intracellular growth

The Gram-negative intracellular pathogen Legionella pneumophila replicates in a membrane-bound compartment known as the Legionella-containing vacuole (LCV), into which it abundantly releases its chaperonin, HtpB. To determine whether HtpB remains within the LCV or reaches the host cell cytoplasm, we infected U937 human macrophages and CHO cells with L. pneumophila expressing a translocation reporter consisting of the Bordetella pertussisa denylate cyclase fused to HtpB. These infections led to increased cyclic AMP levels, suggesting that HtpB reaches the host cell cytoplasm. To identify potential functions of cytoplasmic HtpB, we expressed it in the yeast Saccharomyces cerevisiae, where HtpB induced pseudohyphal growth. A yeast-two-hybrid screen showed that HtpB interacted with S-adenosylmethionine decarboxylase (SAMDC), an essential yeast enzyme (encoded by SPE2) that is required for polyamine biosynthesis. Increasing the copy number of SPE2 induced pseudohyphal growth in S. cerevisiae; thus, we speculated that (i) HtpB induces pseudohyphal growth by activating polyamine synthesis and (ii) L. pneumophila may require exogenous polyamines for growth. A pharmacological inhibitor of SAMDC significantly reduced L. pneumophila replication in L929 mouse cells and U937 macrophages, whereas exogenously added polyamines moderately favored intracellular growth, confirming that polyamines and host SAMDC activity promote L. pneumophila proliferation. Bioinformatic analysis revealed that most known enzymes required for polyamine biosynthesis in bacteria (including SAMDC) are absent in L. pneumophila, further suggesting a need for exogenous polyamines. We hypothesize that HtpB may function to ensure a supply of polyamines in host cells, which are required for the optimal intracellular growth of L. pneumophila.

Biotechnological production of polyamines by bacteria: recent achievements and future perspectives

In Bacteria, the pathways of polyamine biosynthesis start with the amino acids L-lysine, L-ornithine, L-arginine, or L-aspartic acid. Some of these polyamines are of special interest due to their use in the production of engineering plastics (e.g., polyamides) or as curing agents in polymer applications. At present, the polyamines for industrial use are mainly synthesized on chemical routes. However, since a commercial market for polyamines as well as an industry for the fermentative production of amino acid exist, and since bacterial strains overproducing the polyamine precursors L-lysine, L-ornithine, and L-arginine are known, it was envisioned to engineer these amino acid-producing strains for polyamine production. Only recently, researchers have investigated the potential of amino acid-producing strains of Corynebacterium glutamicum and Escherichia coli for polyamine production. This mini-review illustrates the current knowledge of polyamine metabolism in Bacteria, including anabolism, catabolism, uptake, and excretion. The recent advances in engineering the industrial model bacteria C. glutamicum and E. coli for efficient production of the most promising polyamines, putrescine (1,4-diaminobutane), and cadaverine (1,5-diaminopentane), are discussed in more detail.

A novel putrescine importer required for type 1 pili-driven surface motility induced by extracellular putrescine in Escherichia coli K-12

Recently, many studies have reported that polyamines play a role in bacterial cell-to-cell signaling processes. The present study describes a novel putrescine importer required for induction of type 1 pili-driven surface motility. The surface motility of the Escherichia coli ΔspeAB ΔspeC ΔpotABCD strain, which cannot produce putrescine and cannot import spermidine from the medium, was induced by extracellular putrescine. Introduction of the gene deletions for known polyamine importers (ΔpotE, ΔpotFGHI, and ΔpuuP) or a putative polyamine importer (ΔydcSTUV) into the ΔspeAB ΔspeC ΔpotABCD strain did not affect putrescine-induced surface motility. The deletion of yeeF, an annotated putative putrescine importer, in the ΔspeAB ΔspeC ΔpotABCD ΔydcSTUV strain abolished surface motility in putrescine-supplemented medium. Complementation of yeeF by a plasmid vector restored surface motility. The surface motility observed in the present study was abolished by the deletion of fimA, suggesting that the surface motility is type 1 pili-driven. A transport assay using the yeeF(+) or ΔyeeF strains revealed that YeeF is a novel putrescine importer. The K(m) of YeeF (155 μM) is 40 to 300 times higher than that of other importers reported previously. On the other hand, the V(max) of YeeF (9.3 nmol/min/mg) is comparable to that of PotABCD, PotFGHI, and PuuP. The low affinity of YeeF for putrescine may allow E. coli to sense the cell density depending on the concentration of extracellular putrescine.

Evolution of substrate specificity within a diverse family of beta/alpha-barrel-fold basic amino acid decarboxylases: X-ray structure determination of enzymes with specificity for L-arginine and carboxynorspermidine

Pyridoxal 5'-phosphate (PLP)-dependent basic amino acid decarboxylases from the beta/alpha-barrel-fold class (group IV) exist in most organisms and catalyze the decarboxylation of diverse substrates, essential for polyamine and lysine biosynthesis. Herein we describe the first x-ray structure determination of bacterial biosynthetic arginine decarboxylase (ADC) and carboxynorspermidine decarboxylase (CANSDC) to 2.3- and 2.0-A resolution, solved as product complexes with agmatine and norspermidine. Despite low overall sequence identity, the monomeric and dimeric structures are similar to other enzymes in the family, with the active sites formed between the beta/alpha-barrel domain of one subunit and the beta-barrel of the other. ADC contains both a unique interdomain insertion (4-helical bundle) and a C-terminal extension (3-helical bundle) and it packs as a tetramer in the asymmetric unit with the insertions forming part of the dimer and tetramer interfaces. Analytical ultracentrifugation studies confirmed that the ADC solution structure is a tetramer. Specificity for different basic amino acids appears to arise primarily from changes in the position of, and amino acid replacements in, a helix in the beta-barrel domain we refer to as the "specificity helix." Additionally, in CANSDC a key acidic residue that interacts with the distal amino group of other substrates is replaced by Leu(314), which interacts with the aliphatic portion of norspermidine. Neither product, agmatine in ADC nor norspermidine in CANSDC, form a Schiff base to pyridoxal 5'-phosphate, suggesting that the product complexes may promote product release by slowing the back reaction. These studies provide insight into the structural basis for the evolution of novel function within a common structural-fold.

Regulation of gene expression during swarmer cell differentiation in Proteus mirabilis

The gram-negative bacterium Proteus mirabilis can exist in either of two cell types, a vegetative cell characterized as a short rod and a highly elongated and hyperflagellated swarmer cell. This differentiation is triggered by growth on solid surfaces and multiple inputs are sensed by the cell to initiate the differentiation process. These include the inhibition of flagellar rotation, the accumulation of extracellular putrescine and O-antigen interactions with a surface. A key event in the differentiation process is the upregulation of FlhD(2)C(2), which activates the flagellar regulon and additional genes required for differentiation. There are a number of genes that influence FlhD(2)C(2) expression and the function of these genes, if known, will be discussed in this review. Additional genes that have been shown to regulate gene expression during swarming will also be reviewed. Although P. mirabilis represents an excellent system to study microbial differentiation, it is largely understudied relative to other systems. Therefore, this review will also discuss some of the unanswered questions that are central to understanding this process in P. mirabilis.

Loss of the waaL O-antigen ligase prevents surface activation of the flagellar gene cascade in Proteus mirabilis

Proteus mirabilis is a Gram-negative bacterium that undergoes a physical and biochemical change from a vegetative swimmer cell (a typical Gram-negative rod) to an elongated swarmer cell when grown on a solid surface. In this study, we report that a transposon insertion in the waaL gene, encoding O-antigen ligase, blocked swarming motility on solid surfaces but had little effect on swimming motility in soft agar. The waaL mutant was unable to differentiate into a swarmer cell. Differentiation was also prevented by a mutation in wzz, encoding a chain length determinant for O antigen, but not by a mutation in wzyE, encoding an enzyme that polymerizes enterobacterial common antigen, a surface polysaccharide different from the lipid A::core. In wild-type P. mirabilis, increased expression of the flhDC operon occurs after growth on solid surfaces and is required for the high-level expression of flagellin that is characteristic of swarmer cells. However, in both the waaL and the wzz mutants, the flhDC operon was not activated during growth on agar. A loss-of-function mutation in the rcsB response regulator or overexpression of flhDC restored swarming to the waaL mutant, despite the absence of O antigen. Therefore, although O antigen may serve a role in swarming by promoting wettability, the loss of O antigen blocks a regulatory pathway that links surface contact with the upregulation of flhDC expression.

Transcriptome of swarming Proteus mirabilis

Swarming motility by the urinary tract pathogen Proteus mirabilis has been a long-studied but little understood phenomenon. On agar, a P. mirabilis colony grows outward in a bull's-eye pattern formed by consecutive waves of rapid swarming followed by consolidation into shorter cells. To examine differential gene expression in these growth phases, a microarray was constructed based on the completed genome sequence and annotation. RNA was extracted from broth-cultured, swarming, and consolidation-phase cells to assess transcription during each of these growth states. A total of 587 genes were differentially expressed in broth-cultured cells versus swarming cells, and 527 genes were differentially expressed in broth-cultured cells versus consolidation-phase cells (consolidate). Flagellar genes were highly upregulated in both swarming cells and consolidation-phase cells. Fimbriae were downregulated in swarming cells, while genes involved in cell division and anaerobic growth were upregulated in broth-cultured cells. Direct comparison of swarming cells to consolidation-phase cells found that 541 genes were upregulated in consolidate, but only nine genes were upregulated in swarm cells. Genes involved in flagellar biosynthesis, oligopeptide transport, amino acid import and metabolism, cell division, and phage were upregulated in consolidate. Mutation of dppA, oppB, and cysJ, upregulated during consolidation compared to during swarming, revealed that although these genes play a minor role in swarming, dppA and cysJ are required during ascending urinary tract infection. Swarming on agar to which chloramphenicol had been added suggested that protein synthesis is not required for swarming. These data suggest that the consolidation phase is a state in which P. mirabilis prepares for the next wave of swarming.

An alternative polyamine biosynthetic pathway is widespread in bacteria and essential for biofilm formation in Vibrio cholerae

Polyamines are small organic cations found in all cells, and the biosynthetic pathway is well described in eukaryotes and Escherichia coli. The characterized pathway uses decarboxylated S-adenosylmethionine as the aminopropyl group donor to form spermidine from putrescine by the key enzymes S-adenosylmethionine decarboxylase and spermidine synthase. We report here the in vivo characterization of an alternative polyamine biosynthetic pathway from Vibrio cholerae, the causative agent of human cholera. The pathway uses aspartate beta-semialdehyde as the aminopropyl group donor and consists of a fused protein containing l-2,4-diaminobutyrate aminotransferase and l-2,4-diaminobutyrate decarboxylase, a carboxynorspermidine dehydrogenase (CANSDH), and a carboxynorspermidine decarboxylase (CANSDC). We show that in V. cholerae, this pathway is required for synthesis of both sym-norspermidine and spermidine. Heterologous expression of the V. cholerae pathway in E. coli results in accumulation of the nonnative polyamines diaminopropane and sym-norspermidine. Genetic deletion of the V. cholerae CANSDC led to accumulation of carboxynorspermidine, whereas deletion of either CANSDC or the putative CANSDH led to loss of sym-norspermidine and spermidine. These results allowed unambiguous identification of the gene encoding CANSDH. Furthermore, deletion of either CANSDH or CANSDC led to a 50-60% reduction in growth rate of planktonic cells and severely reduced biofilm formation, which could be rescued by exogenously supplied sym-norspermidine but not spermidine. The pathway was not required for infectivity in a mouse model of V. cholerae infection. Notably, the alternative polyamine biosynthetic pathway is widespread in bacteria and is likely to play a previously unrecognized role in the biology of these organisms.

The putrescine Importer PuuP of Escherichia coli K-12

The Puu pathway is a putrescine utilization pathway involving gamma-glutamyl intermediates. The genes encoding the enzymes of the Puu pathway form a gene cluster, the puu gene cluster, and puuP is one of the genes in this cluster. In Escherichia coli, three putrescine importers, PotFGHI, PotABCD, and PotE, were discovered in the 1990s and have been studied; however, PuuP had not been discovered previously. This paper shows that PuuP is a novel putrescine importer whose kinetic parameters are equivalent to those of the polyamine importers discovered previously. A puuP(+) strain absorbed up to 5 mM putrescine from the medium, but a DeltapuuP strain did not. E. coli strain MA261 has been used in previous studies of polyamine transporters, but PuuP had not been identified previously. It was revealed that the puuP gene of MA261 was inactivated by a point mutation. When E. coli was grown on minimal medium supplemented with putrescine as the sole carbon or nitrogen source, only PuuP among the polyamine importers was required. puuP was expressed strongly when putrescine was added to the medium or when the puuR gene, which encodes a putative repressor, was deleted. When E. coli was grown in M9-tryptone medium, PuuP was expressed mainly in the exponential growth phase, and PotFGHI was expressed independently of the growth phase.

Bacterial Swarming: A Model System for Studying Dynamic Self-assembly

Bacterial swarming is an example of dynamic self-assembly in microbiology in which the collective interaction of a population of bacterial cells leads to emergent behavior. Swarming occurs when cells interact with surfaces, reprogram their physiology and behavior, and adapt to changes in their environment by coordinating their growth and motility with other cells in the colony. This review summarizes the salient biological and biophysical features of this system and describes our current understanding of swarming motility. We have organized this review into four sections: 1) The biophysics and mechanisms of bacterial motility in fluids and its relevance to swarming. 2) The role of cell/molecule, cell/surface, and cell/cell interactions during swarming. 3) The changes in physiology and behavior that accompany swarming motility. 4) A concluding discussion of several interesting, unanswered questions that is particularly relevant to soft matter scientists.

The effect of monoterpenes on swarming differentiation and haemolysin activity in Proteus mirabilis

Urinary tract infection by Proteus mirabilis depends on several virulence properties that are coordinately regulated with swarming differentiation. Here we report the antibacterial and anti-swarming effect of seventeen terpenoids, and the effect of subinhibitory concentrations of five selected terpenoids on swarming, biofilm formation and haemolysin activity. The results showed that all the terpenes evaluated, particularly oxygenated terpenoids, inhibited P. mirabilis with MIC values ranging between 3 and 10 mg/L. Moreover, citral, citronellol and geraniol effectively inhibit P. mirabilis swarming in a dose dependent manner, reducing swimming/swarming cell differentiation and haemolysin activity at 1/10 MIC concentration. The inhibition of P. mirabilis swarming and virulence factor expression by selected oxygenated terpenoids suggest that essential oils with high concentration of these compounds have the potential to be developed as products for preventing P. mirabilis infections.

Living on a surface: swarming and biofilm formation

Swarming is the fastest known bacterial mode of surface translocation and enables the rapid colonization of a nutrient-rich environment and host tissues. This complex multicellular behavior requires the integration of chemical and physical signals, which leads to the physiological and morphological differentiation of the bacteria into swarmer cells. Here, we provide a review of recent advances in the study of the regulatory pathways that lead to swarming behavior of different model bacteria. It has now become clear that many of these pathways also affect the formation of biofilms, surface-attached bacterial colonies. Decision-making between rapidly colonizing a surface and biofilm formation is central to bacterial survival among competitors. In the second part of this article, we review recent developments in the understanding of the transition between motile and sessile lifestyles of bacteria.

Complete genome sequence of uropathogenic Proteus mirabilis, a master of both adherence and motility

The gram-negative enteric bacterium Proteus mirabilis is a frequent cause of urinary tract infections in individuals with long-term indwelling catheters or with complicated urinary tracts (e.g., due to spinal cord injury or anatomic abnormality). P. mirabilis bacteriuria may lead to acute pyelonephritis, fever, and bacteremia. Most notoriously, this pathogen uses urease to catalyze the formation of kidney and bladder stones or to encrust or obstruct indwelling urinary catheters. Here we report the complete genome sequence of P. mirabilis HI4320, a representative strain cultured in our laboratory from the urine of a nursing home patient with a long-term (> or =30 days) indwelling urinary catheter. The genome is 4.063 Mb long and has a G+C content of 38.88%. There is a single plasmid consisting of 36,289 nucleotides. Annotation of the genome identified 3,685 coding sequences and seven rRNA loci. Analysis of the sequence confirmed the presence of previously identified virulence determinants, as well as a contiguous 54-kb flagellar regulon and 17 types of fimbriae. Genes encoding a potential type III secretion system were identified on a low-G+C-content genomic island containing 24 intact genes that appear to encode all components necessary to assemble a type III secretion system needle complex. In addition, the P. mirabilis HI4320 genome possesses four tandem copies of the zapE metalloprotease gene, genes encoding six putative autotransporters, an extension of the atf fimbrial operon to six genes, including an mrpJ homolog, and genes encoding at least five iron uptake mechanisms, two potential type IV secretion systems, and 16 two-component regulators.

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

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

Characterization of a novel gene, wosA, regulating FlhDC expression in Proteus mirabilis

In this study, we describe wosA, a Proteus mirabilis gene identified by its ability to increase swarming motility when overexpressed. At various times during the swarming cycle, the increased expression of wosA resulted in a 4- to 16-fold upregulation of the transcription of flhDC, encoding the master regulator of the flagellar cascade. In turn, the expression of flaA, encoding flagellin, was substantially increased in wosA-overexpressing strains. The overexpression of wosA also resulted in constitutive swarmer cell differentiation in liquid medium, a normally nonpermissive condition. However, in wosA-overexpressing strains, the onset of swarming was not altered. A null wosA allele resulted in a slight decrease in swarming motility. The expression of wosA was growth phase dependent during growth in liquid and on agar plates during swarmer cell differentiation. Increasing the viscosity of liquid medium by the addition of polyvinylpyrrolidone induced swarmer cell differentiation and resulted in a fourfold increase in wosA transcription. A fliL mutation that results in constitutive swarmer cell elongation also increased wosA transcription. In this study, we discuss the possible role of the wosA gene product in signal transduction from solid surfaces to induce swarmer cell differentiation, possibly via alterations in the motor switch complex. This study also suggests that despite constitutive swarmer cell differentiation in wosA-overexpressing strains, there are additional regulatory and/or environmental conditions that may control the onset of swarming migration.

Genetic determinants of swarming in Rhizobium etli

Swarming motility is considered to be a social phenomenon that enables groups of bacteria to move coordinately atop solid surfaces. The differentiated swarmer cell population is embedded in an extracellular slime layer, and the phenomenon has previously been linked with biofilm formation and virulence. The gram-negative nitrogen-fixing soil bacterium Rhizobium etli CNPAF512 was previously shown to display swarming behavior on soft agar plates. In a search for novel genetic determinants of swarming, a detailed analysis of the swarming behavior of 700 miniTn5 mutants of R. etli was performed. Twenty-four mutants defective in swarming or displaying abnormal swarming patterns were identified and could be divided into three groups based on their swarming pattern. Fourteen mutants were completely swarming deficient, five mutants showed an atypical swarming pattern with no completely smooth edge and local extrusions, and five mutants displayed an intermediate swarming phenotype. Sequence analysis of the targeted genes indicated that the mutants were likely affected in quorum-sensing, polysaccharide composition or export, motility, and amino acid and polyamines metabolism. Several of the identified mutants displayed a reduced symbiotic nitrogen fixation activity.

Analysis of Yersinia pestis gene expression in the flea vector

Yersinia pestis is the causative agent of plague. Unlike the other pathogenic Yersinia species, Y. pestis has evolved an arthropod-borne route of transmission, alternately infecting flea and mammalian hosts. Distinct subsets of genes are hypothesized to be differentially expressed during infection of the arthropod vector and mammalian host. Genes crucial for mammalian infection are referred to as virulence factors whilst genes playing a role in the flea vector are termed transmission factors. This article serves as a review of known factors involved in flea-borne transmission and introduces an 'in vivo' microarray approach to elucidating the genetic basis of Y. pestis infection of- and transmission by the flea.