High affinity iron uptake by pyoverdine in Pseudomonas aeruginosa involves multiple regulators besides Fur, PvdS, and FpvI.

Pseudomonas aeruginosa is a Gram-negative bacterium which can cause serious infections among immune-depressed people including cystic fibrosis patients where it can colonize the lungs causing chronic infections. Iron is essential for P. aeruginosa and can be provided via three sources under aerobic conditions: its own siderophores pyochelin (PCH) and pyoverdine (PVD), xenosiderophores, or heme, respectively. Pyoverdine is the high affinity siderophore and its synthesis and uptake involve more than 30 genes organized in different operons. Its synthesis and uptake are triggered by iron scarcity via the Fur regulator and involves two extra cytoplasmic sigma factors (ECF), PvdS for the biosynthesis of PVD and FpvI for the uptake via the TonB-dependent FpvA outer membrane transporter and other periplasmic and inner membrane proteins. It appeared recently that the regulation of PVD biosynthesis and uptake involves other regulators, including other ECF factors, and LysR regulators. This is the case especially for the genes coding for periplasmic and inner membrane proteins involved in the reduction of Fe3+ to Fe2+ and the transport of ferrous iron to the cytoplasm that appears to represent a crucial step in the uptake process.

Cell Envelope Stress Response in Pseudomonas aeruginosa.

Bacteria sense their environment via the cell envelope, which in Gram-negative bacteria comprises the outer membrane, the periplasmic space, and the inner membrane. Pseudomonas aeruginosa is an opportunistic pathogen which is exposed to different cell wall stresses imposed by exposure to antibiotics, osmotic pressure, and long-time colonization of host tissues such as the lung in cystic fibrosis patients. In response to these stresses, P. aeruginosa is able to respond by establishing a cell envelope stress response involving different regulatory pathways including the extra-cytoplasmic sigma factors AlgU, SigX, and SbrI and other two-component sensor/response regulators and effectors. This chapter aims to review the different factors leading to the activation of the cell envelope stress response in P. aeruginosa and the genetic determinants involved in this response, which is crucial for the survival of the bacterium upon exposure to different stressful conditions.

Intrapulmonary percussive ventilation improves lung function in cystic fibrosis patients chronically colonized with Pseudomonas aeruginosa: a pilot cross-over study.

High levels of shear stress can prevent and disrupt Pseudomonas aeruginosa biofilm formation in vitro. Intrapulmonary percussive ventilation (IPV) could be used to introduce shear stress into the lungs of cystic fibrosis (CF) patients to disrupt biofilms in vivo. We performed a first-of-its-kind pilot clinical study to evaluate short-term IPV therapy at medium (200 bursts per minute, bpm) and high frequency (400 bpm) as compared to autogenic drainage (AD) on lung function and the behavior of P. aeruginosa in the CF lung in four patients who are chronically colonized by P. aeruginosa. A significant difference between the three treatment groups was observed for both the forced expiratory volume in 1 s (FEV1) and the forced vital capacity (FVC) (p < 0.05). More specifically, IPV at high frequency significantly increased FEV1 and FVC compared to AD (p < 0.05) and IPV at medium frequency (p < 0.001). IPV at high frequency enhanced the expression levels of P. aeruginosa planktonic marker genes, which was less pronounced with IPV at medium frequency or AD. In conclusion, IPV at high frequency could potentially alter the behavior of P. aeruginosa in the CF lung and improve lung function. TRIAL REGISTRATION: The trail was retrospectively registered at the ISRCTN registry on 6 June 2013, under trial registration number ISRCTN75391385.

Capture of endogenously biotinylated proteins from Pseudomonas aeruginosa displays unexpected downregulation of LiuD upon iron nutrition.

The uptake and storage but also removal of excess iron are of utmost importance to microorganisms since surplus levels of iron may lead to the formation of reactive oxygen species. Therefore, iron homeostasis is generally tightly regulated by the ferric uptake regulator (Fur), a global iron regulator acting as a transcriptional repressor. While detecting biotinylated proteins in labelling experiments, we discovered that the endogenously biotinylated protein LiuD differentially accumulated upon iron treatment. LiuD represents the α-subunit of the methylcrotonyl-CoA-carboxylase (MCCase), an enzyme from the leucine/isovalerate utilization pathway. Real-time PCR transcription analysis revealed that the observed lower levels of LiuD biotinylation could be traced back to lower LiuD protein levels via a transcriptional repression of liuABCDE expression that however does not seem to be mediated by Fur. In accordance with LiuD's role for the leucine/isovalerate utilization pathway and its protein level regulation by nutritional iron levels, we found that wild-type Pseudomonas aeruginosa did not grow in the presence of iron if the medium contained only leucine as a carbon source. Conversely, iron stimulated the growth when glucose was used as a carbon source. Our study thus demonstrates the complexities of iron-regulated bacterial growth in Pseudomonas aeruginosa.

Origin and functional diversification of an amphibian defense peptide arsenal.

The skin secretion of many amphibians contains an arsenal of bioactive molecules, including hormone-like peptides (HLPs) acting as defense toxins against predators, and antimicrobial peptides (AMPs) providing protection against infectious microorganisms. Several amphibian taxa seem to have independently acquired the genes to produce skin-secreted peptide arsenals, but it remains unknown how these originated from a non-defensive ancestral gene and evolved diverse defense functions against predators and pathogens. We conducted transcriptome, genome, peptidome and phylogenetic analyses to chart the full gene repertoire underlying the defense peptide arsenal of the frog Silurana tropicalis and reconstruct its evolutionary history. Our study uncovers a cluster of 13 transcriptionally active genes, together encoding up to 19 peptides, including diverse HLP homologues and AMPs. This gene cluster arose from a duplicated gastrointestinal hormone gene that attained a HLP-like defense function after major remodeling of its promoter region. Instead, new defense functions, including antimicrobial activity, arose by mutation of the precursor proteins, resulting in the proteolytic processing of secondary peptides alongside the original ones. Although gene duplication did not trigger functional innovation, it may have subsequently facilitated the convergent loss of the original function in multiple gene lineages (subfunctionalization), completing their transformation from HLP gene to AMP gene. The processing of multiple peptides from a single precursor entails a mechanism through which peptide-encoding genes may establish new functions without the need for gene duplication to avoid adaptive conflicts with older ones.

Pseudomonas aeruginosa LysR PA4203 regulator NmoR acts as a repressor of the PA4202 nmoA gene, encoding a nitronate monooxygenase.

The PA4203 gene encodes a LysR regulator and lies between the ppgL gene (PA4204), which encodes a periplasmic gluconolactonase, and, in the opposite orientation, the PA4202 (nmoA) gene, coding for a nitronate monooxygenase, and ddlA (PA4201), encoding a d-alanine alanine ligase. The intergenic regions between PA4203 and ppgL and between PA4203 and nmoA are very short (79 and 107 nucleotides, respectively). Here we show that PA4203 (nmoR) represses its own transcription and the expression of nmoA. A chromatin immunoprecipitation analysis showed the presence of a single NmoR binding site between nmoA and nmoR, which was confirmed by electrophoretic mobility shift assays (EMSAs) with the purified NmoR protein. Despite this observation, a transcriptome analysis revealed more genes to be affected in an nmoR mutant, including genes known to be part of the MexT LysR activator regulon. The PA1225 gene, encoding a quinone oxidoreductase, was the most highly upregulated gene in the nmoR deletion mutant, independently of MexT. Finally, deletion of the nmoA gene resulted in an increased sensitivity of the cells to 3-nitropropionic acid (3-NPA), confirming the role of the nitronate monooxygenase protein in the detoxification of nitronate.

The combined structural and kinetic characterization of a bacterial nitronate monooxygenase from Pseudomonas aeruginosa PAO1 establishes NMO class I and II.

Nitronate monooxygenase (NMO) oxidizes the mitochondrial toxin propionate 3-nitronate (P3N) to malonate semialdehyde. The enzyme has been previously characterized biochemically in fungi, but no structural information is available. Based on amino acid similarity 4,985 genes are annotated in the GenBank(TM) as NMO. Of these, 4,424 (i.e. 89%) are bacterial genes, including several Pseudomonads that have been shown to use P3N as growth substrate. Here, we have cloned and expressed the gene pa4202 of Pseudomonas aeruginosa PAO1, purified the resulting protein, and characterized it. The enzyme is active on P3N and other alkyl nitronates, but cannot oxidize nitroalkanes. P3N is the best substrate at pH 7.5 and atmospheric oxygen with k(cat)(app)/K(m)(app) of 12 × 10(6) M(-1) s(-1), k(cat)(app) of 1300 s(-1), and K(m)(app) of 110 µm. Anerobic reduction of the enzyme with P3N yields a flavosemiquinone, which is formed within 7.5 ms, consistent with this species being a catalytic intermediate. Absorption spectroscopy, mass spectrometry, and x-ray crystallography demonstrate a tightly, non-covalently bound FMN in the active site of the enzyme. Thus, PA4202 is the first NMO identified and characterized in bacteria. The x-ray crystal structure of the enzyme was solved at 1.44 Å, showing a TIM barrel-fold. Four motifs in common with the biochemically characterized NMO from Cyberlindnera saturnus are identified in the structure of bacterial NMO, defining Class I NMO, which includes bacterial, fungal, and two animal NMOs. Notably, the only other NMO from Neurospora crassa for which biochemical evidence is available lacks the four motifs, defining Class II NMO.

HapX-mediated iron homeostasis is essential for rhizosphere competence and virulence of the soilborne pathogen Fusarium oxysporum.

Soilborne fungal pathogens cause devastating yield losses and are highly persistent and difficult to control. During the infection process, these organisms must cope with limited availability of iron. Here we show that the bZIP protein HapX functions as a key regulator of iron homeostasis and virulence in the vascular wilt fungus Fusarium oxysporum. Deletion of hapX does not affect iron uptake but causes derepression of genes involved in iron-consuming pathways, leading to impaired growth under iron-depleted conditions. F. oxysporum strains lacking HapX are reduced in their capacity to invade and kill tomato (Solanum lycopersicum) plants and immunodepressed mice. The virulence defect of ΔhapX on tomato plants is exacerbated by coinoculation of roots with a biocontrol strain of Pseudomonas putida, but not with a siderophore-deficient mutant, indicating that HapX contributes to iron competition of F. oxysporum in the tomato rhizosphere. These results establish a conserved role for HapX-mediated iron homeostasis in fungal infection of plants and mammals.

Antibacterial activity and mutagenesis of sponge-associated Pseudomonas fluorescens H41.

Marine sponges (phylum Porifera) are well known to harbour a complex and diverse bacterial community. Some of these sponge-associated bacteria have been shown to be the real producers of secondary metabolites with a wide range of activities from antimicrobials to anticancer agents. Previously, we revealed that the strain Pseudomonas fluorescens H41 isolated from the sponge Haliclona sp. (collected at the coast of Rio de Janeiro, Brazil) showed a strong antimicrobial activity against clinical and marine bacteria. Thus, in this study the genes involved in the antimicrobial activity of P. fluorescens H41 were identified. To this end, a library of mutants was generated via miniTnphoA3 transposon mutagenesis and the resulting clones were characterized for their antimicrobial activity. It was demonstrated that genes involved in the biosynthesis of the pyoverdine siderophore are related to the inhibitory activity of P. fluorescens H41. Therefore, this strain might play an important role in the biocontrol of the host sponge.

Pore-forming pyocin S5 utilizes the FptA ferripyochelin receptor to kill Pseudomonas aeruginosa.

Pyocins are toxic proteins produced by some strains of Pseudomonas aeruginosa that are lethal for related strains of the same species. Some soluble pyocins (S2, S3 and S4) were previously shown to use the pyoverdine siderophore receptors to enter the cell. The P. aeruginosa PAO1 pore-forming pyocin S5 encoding gene (PAO985) was cloned into the expression vector pET15b, and the affinity-purified protein product tested for its killing activity against different P. aeruginosa strains. The results, however, did not show any correlation with a specific ferripyoverdine receptor. To further identify the S5 receptor, transposon mutants were generated. Pooled mutants were exposed to pyocin S5 and the resistant colonies growing in the killing zone were selected. The majority of S5-resistant mutants had an insertion in the fptA gene encoding the receptor for the siderophore pyochelin. Complementation of an fptA transposon mutant with the P. aeruginosa fptA gene in trans restored the sensitivity to S5. In order to define the receptor-binding domain of pyocin S5, two hybrid pyocins were constructed containing different regions from pyocin S5 fused to the C-terminal translocation and DNase killing domains of pyocin S2. Only the protein containing amino acid residues 151 to 300 from S5 showed toxicity, indicating that the pyocin S5 receptor-binding domain is not at the N-terminus of the protein as in other S-type pyocins. Pyocin S5 was, however, unable to kill Burkholderia cenocepacia strains producing a ferripyochelin FptA receptor, nor was the B. cenocepacia fptA gene able to restore the sensitivity of the resistant fptA mutant P. aeruginosa strain.

The skin microbiome of caspase-14-deficient mice shows mild dysbiosis.

Caspase-14, an important proteinase involved in filaggrin catabolism, is mainly active in terminally differentiating keratinocytes, where it is required for the generation of skin natural moisturizing factors (NMFs). Consequently, caspase-14 deficient epidermis is characterized by reduced levels of NMFs such as urocanic acid and 2-pyrrolidone-5-carboxylic acid. Patients suffering from filaggrin deficiency are prone to develop atopic dermatitis, which is accompanied with increased microbial burden. Among several reasons, this effect could be due to a decrease in filaggrin breakdown products. In this study, we found that caspase-14(-/-) mice show enhanced antibacterial response compared to wild-type mice when challenged with bacteria. Therefore, we compared the microbial communities between wild-type and caspase-14(-/-) mice by sequencing of bacterial 16S ribosomal RNA genes. We observed that caspase-14 ablation leads to an increase in bacterial richness and diversity during steady-state conditions. Although both wild-type and caspase-14(-/-) skin were dominated by the Firmicutes phylum, the Staphylococcaceae family was reduced in caspase-14(-/-) mice. Altogether, our data demonstrated that caspase-14 deficiency causes the imbalance of the skin-resident bacterial communities.

Analysis of the draft genome of Pseudomonas fluorescens ATCC17400 indicates a capacity to take up iron from a wide range of sources, including different exogenous pyoverdines.

All fluorescent pseudomonads (Pseudomonas aeruginosa, P. putida, P. fluorescens, P. syringae and others) are known to produce the high-affinity peptidic yellow-green fluorescent siderophore pyoverdine. These siderophores have peptide chains that are quite diverse and more than 50 pyoverdine structures have been elucidated. In the majority of the cases, a Pseudomonas species is also able to produce a second siderophore of lower affinity for iron. Pseudomonas fluorescens ATCC 17400 has been shown to produce a unique second siderophore, (thio)quinolobactin, which has an antimicrobial activity against the phytopathogenic Oomycete Pythium debaryanum. We show that this strain has the capacity to utilize 16 different pyoverdines, suggesting the presence of several ferripyoverdine receptors. Analysis of the draft genome of P. fluorescens ATCC 17400 confirmed the presence of 55 TonB-dependent receptors, the largest so far for Pseudomonas, among which 15 are predicted to be ferripyoverdine receptors (Fpv). Phylogenetic analysis revealed the presence of two different clades containing ferripyoverdine receptors, with sequences similar to the P. aeruginosa type II FpvA forming a separate cluster. Among the other receptors we confirmed the presence of the QbsI (thio)quinolobactin receptor, an ferri-achromobactin and an ornicorrugatin receptor, several catecholate and four putative heme receptors. Twenty five of the receptors genes were found to be associated with genes encoding extracytoplasmic sigma factors (ECF σ) and transmembrane anti-σ sensors.

Global regulation of gene expression by OxyR in an important human opportunistic pathogen.

Most bacteria control oxidative stress through the H(2)O(2)-responsive transactivator OxyR, a member of the LTTR family (LysR Type Transcriptional Regulators), which activates the expression of defensive genes such as those encoding catalases, alkyl hydroperoxide reductases and superoxide dismutases. In the human opportunistic pathogen Pseudomonas aeruginosa, OxyR positively regulates expression of the oxidative stress response genes katA, katB, ahpB and ahpCF. To identify additional targets of OxyR in P. aeruginosa PAO1, we performed chromatin immunoprecipitation in combination with whole genome tiling array analyses (ChIP-chip). We detected 56 genes including all the previously identified defensive genes and a battery of novel direct targets of OxyR. Electrophoretic mobility shift assays (EMSAs) for selected newly identified targets indicated that ∼70% of those were bound by purified oxidized OxyR and their regulation was confirmed by quantitative real-time polymerase chain reaction. Furthermore, a thioredoxin system was identified to enzymatically reduce OxyR under oxidative stress. Functional classification analysis showed that OxyR controls a core regulon of oxidative stress defensive genes, and other genes involved in regulation of iron homeostasis (pvdS), quorum-sensing (rsaL), protein synthesis (rpsL) and oxidative phosphorylation (cyoA and snr1). Collectively, our results indicate that OxyR is involved in oxidative stress defense and regulates other aspects of cellular metabolism as well.

cmpX overexpression in Pseudomonas aeruginosa affects biofilm formation and cell morphology in response to shear stress.

Pseudomonas aeruginosa is an opportunistic pathogen causing chronic infections that are related to its ability to form biofilms. Mechanosensitive ion channels (Mcs) are cytoplasmic membrane proteins whose opening depends on a mechanical stress impacting the lipid bilayer. CmpX is a homologue of the small conductance MscS of Escherichia coli. The cmpX gene is part of a transcriptional cfrX-cmpX unit that is under the control of the cell envelope stress response ECF sigma factor SigX. CmpX was shown to regulate the activity of the hybrid sensor kinase PA1611 involved in the regulation of transition from a planktonic to a biofilm lifestyle. The deletion of cmpX leads to increased biofilm formation under static conditions. Herein, the effect of cmpX overexpression was investigated by confocal laser scanning microscopy in terms of biofilm formation and architecture, and matrix components production, in dynamic conditions. We show that overexpression of cmpX in P. aeruginosa leads to enhanced and altered biofilm architecture that seems to be associated to increased matrix components and the emergence of filamentous cells. These phenotypic alterations might occur potentially through a shear stress induced by the medium flow rate. Importance: CmpX is involved in biofilm formation and cell filamentation with regards to the medium flow.

Membrane fluidity homeostasis is required for tobramycin-enhanced biofilm in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic pathogen, which causes chronic infections, especially in cystic fibrosis (CF) patients where it colonizes the lungs via the build-up of biofilms. Tobramycin, an aminoglycoside, is often used to treat P. aeruginosa infections in CF patients. Tobramycin at sub-minimal inhibitory concentrations enhances both biofilm biomass and thickness in vitro; however, the mechanism(s) involved are still unknown. Herein, we show that tobramycin increases the expression and activity of SigX, an extracytoplasmic sigma factor known to be involved in the biosynthesis of membrane lipids and membrane fluidity homeostasis. The biofilm enhancement by tobramycin is not observed in a sigX mutant, and the sigX mutant displays increased membrane stiffness. Remarkably, the addition of polysorbate 80 increases membrane fluidity of sigX-mutant cells in biofilm, restoring the tobramycin-enhanced biofilm formation. Our results suggest the involvement of membrane fluidity homeostasis in biofilm development upon tobramycin exposure.IMPORTANCEPrevious studies have shown that sub-lethal concentrations of tobramycin led to an increase biofilm formation in the case of infections with the opportunistic pathogen Pseudomonas aeruginosa. We show that the mechanism involved in this phenotype relies on the cell envelope stress response, triggered by the extracytoplasmic sigma factor SigX. This phenotype was abolished in a sigX-mutant strain. Remarkably, we show that increasing the membrane fluidity of the mutant strain is sufficient to restore the effect of tobramycin. Altogether, our data suggest the involvement of membrane fluidity homeostasis in biofilm development upon tobramycin exposure.

A combinatorial approach to the structure elucidation of a pyoverdine siderophore produced by a Pseudomonas putida isolate and the use of pyoverdine as a taxonomic marker for typing P. putida subspecies.

The structure of a pyoverdine produced by Pseudomonas putida, W15Oct28, was elucidated by combining mass spectrometric methods and bioinformatics by the analysis of non-ribosomal peptide synthetase genes present in the newly sequenced genome. The only form of pyoverdine produced by P. putida W15Oct28 is characterized to contain α-ketoglutaric acid as acyl side chain, a dihydropyoverdine chromophore, and a 12 amino acid peptide chain. The peptide chain is unique among all pyoverdines produced by Pseudomonas subspecies strains. It was characterized as -L-Asp-L-Ala-D-AOHOrn-L-Thr-Gly-c[L-Thr(O-)-L-Hse-D-Hya-L-Ser-L-Orn-L-Hse-L-Ser-O-]. The chemical formula and the detected and calculated molecular weight of this pyoverdine are: C65H93N17O32, detected mass 1624.6404 Da, calculated mass 1624.6245. Additionally, pyoverdine structures from both literature reports and bioinformatics prediction of the genome sequenced P. putida strains are summarized allowing us to propose a scheme based on pyoverdines structures as tool for the phylogeny of P. putida. This study shows the strength of the combination of in silico analysis together with analytical data and literature mining in determining the structure of secondary metabolites such as peptidic siderophores.

Chenodeoxycholic Acid-Amikacin Combination Enhances Eradication of Staphylococcus aureus.

The rise of antibiotic resistance and dearth of novel antibiotics have posed a serious health crisis worldwide. In this study, we screened a combination of antibiotics and nonantibiotics providing a viable strategy to solve this issue by broadening the antimicrobial spectrum. We found that chenodeoxycholic acid (CDCA), a cholic acid derivative of the traditional Chinese medicine (TCM) Tanreqing (TRQ), synergizes with amikacin against Staphylococcus aureus in vitro, and this synergistic killing was effective against diverse methicillin-resistant S. aureus (MRSA) variants, including small-colony variants (SCVs), biofilm strains, and persisters. The CDCA-amikacin combination protects a mouse model from S. aureus infections. Mechanistically, CDCA increases the uptake of aminoglycosides in a proton motive force-dependent manner by dissipating the chemical potential and potentiates reactive oxygen species (ROS) generation by inhibiting superoxide dismutase activity. This work highlights the potential use of TCM components in treating S. aureus-associated infections and extend the use of aminoglycosides in eradicating Gram-positive pathogens. IMPORTANCE Multidrug resistance (MDR) is spreading globally with increasing speed. The search for new antibiotics is one of the key strategies in the fight against MDR. Antibiotic resistance breakers that may or may not have direct antibacterial action and can either be coadministered or conjugated with other antibiotics are being studied. To better expand the antibacterial spectrum of certain antibiotics, we identified one component from a traditional Chinese medicine, Tanreqing (TRQ), that increased the activity of aminoglycosides. We found that this so-called agent, chenodeoxycholic acid (CDCA), sensitizes Staphylococcus aureus to aminoglycoside killing and protects a mouse model from S. aureus infections. CDCA increases the uptake of aminoglycosides in a proton motive force-dependent manner by dissipating the chemical potential and potentiates ROS generation by inhibiting superoxide dismutase activity in S. aureus. Our work highlights the potential use of TCM or its effective components, such as CDCA, in treating antibiotic resistance-associated infections.

The natriuretic peptide receptor agonist osteocrin disperses Pseudomonas aeruginosa biofilm.

Biofilms are highly tolerant to antimicrobials and host immune defense, enabling pathogens to thrive in hostile environments. The diversity of microbial biofilm infections requires alternative and complex treatment strategies. In a previous work we demonstrated that the human Atrial Natriuretic Peptide (hANP) displays a strong anti-biofilm activity toward Pseudomonas aeruginosa and that the binding of hANP by the AmiC protein supports this effect. This AmiC sensor has been identified as an analog of the human natriuretic peptide receptor subtype C (h-NPRC). In the present study, we evaluated the anti-biofilm activity of the h-NPRC agonist, osteocrin (OSTN), a hormone that displays a strong affinity for the AmiC sensor at least in vitro. Using molecular docking, we identified a pocket in the AmiC sensor that OSTN reproducibly docks into, suggesting that OSTN might possess an anti-biofilm activity as well as hANP. This hypothesis was validated since we observed that OSTN dispersed established biofilm of P. aeruginosa PA14 strain at the same concentrations as hANP. However, the OSTN dispersal effect is less marked than that observed for the hANP (-61% versus -73%). We demonstrated that the co-exposure of P. aeruginosa preformed biofilm to hANP and OSTN induced a biofilm dispersion with a similar effect to that observed with hANP alone suggesting a similar mechanism of action of these two peptides. This was confirmed by the observation that OSTN anti-biofilm activity requires the activation of the complex composed by the sensor AmiC and the regulator AmiR of the ami pathway. Using a panel of both P. aeruginosa laboratory reference strains and clinical isolates, we observed that the OSTN capacity to disperse established biofilms is highly variable from one strain to another. Taken together, these results show that similarly to the hANP hormone, OSTN has a strong potential to be used as a tool to disperse P. aeruginosa biofilms.

A long-branch attraction artifact reveals an adaptive radiation in pseudomonas.

A significant proportion of protein-encoding gene phylogenies in bacteria is inconsistent with the species phylogeny. It was usually argued that such inconsistencies resulted from lateral transfers. Here, by further studying the phylogeny of the oprF gene encoding the major surface protein in the bacterial Pseudomonas genus, we found that the incongruent tree topology observed results from a long-branch attraction (LBA) artifact and not from lateral transfers. LBA in the oprF phylogeny could be explained by the faster evolution in a lineage adapted to the rhizosphere, highlighting an unexpected adaptive radiation. We argue that analysis of such artifacts in other inconsistent bacterial phylogenies could be a valuable tool in molecular ecology to highlight cryptic adaptive radiations in microorganisms.