Threshold Resummation for the Production of Four Top Quarks at the LHC.

We compute the total cross section for tt[over ¯]tt[over ¯] production at next-to-leading logarithmic (NLL^{'}) accuracy. This is the first time resummation is performed for a hadron-collider process with four colored particles in the final state. The calculation is matched to the next-to-leading order strong and electroweak corrections. The NLL^{'} corrections enhance the total production rate by 15%. The size of the theoretical error due to scale variation is reduced by more than a factor of 2, bringing the theoretical error significantly below the current experimental uncertainty of the measurement.

More than 18,000 effectors in the Legionella genus genome provide multiple, independent combinations for replication in human cells.

The genus Legionella comprises 65 species, among which Legionella pneumophila is a human pathogen causing severe pneumonia. To understand the evolution of an environmental to an accidental human pathogen, we have functionally analyzed 80 Legionella genomes spanning 58 species. Uniquely, an immense repository of 18,000 secreted proteins encoding 137 different eukaryotic-like domains and over 200 eukaryotic-like proteins is paired with a highly conserved type IV secretion system (T4SS). Specifically, we show that eukaryotic Rho- and Rab-GTPase domains are found nearly exclusively in eukaryotes and Legionella Translocation assays for selected Rab-GTPase proteins revealed that they are indeed T4SS secreted substrates. Furthermore, F-box, U-box, and SET domains were present in >70% of all species, suggesting that manipulation of host signal transduction, protein turnover, and chromatin modification pathways are fundamental intracellular replication strategies for legionellae. In contrast, the Sec-7 domain was restricted to L. pneumophila and seven other species, indicating effector repertoire tailoring within different amoebae. Functional screening of 47 species revealed 60% were competent for intracellular replication in THP-1 cells, but interestingly, this phenotype was associated with diverse effector assemblages. These data, combined with evolutionary analysis, indicate that the capacity to infect eukaryotic cells has been acquired independently many times within the genus and that a highly conserved yet versatile T4SS secretes an exceptional number of different proteins shaped by interdomain gene transfer. Furthermore, we revealed the surprising extent to which legionellae have coopted genes and thus cellular functions from their eukaryotic hosts, providing an understanding of how dynamic reshuffling and gene acquisition have led to the emergence of major human pathogens.

Evolution and function of bacterial RCC1 repeat effectors.

Intracellular bacterial pathogens harbour genes, the closest homologues of which are found in eukaryotes. Regulator of chromosome condensation 1 (RCC1) repeat proteins are phylogenetically widespread and implicated in protein-protein interactions, such as the activation of the small GTPase Ran by its cognate guanine nucleotide exchange factor, RCC1. Legionella pneumophila and Coxiella burnetii, the causative agents of Legionnaires' disease and Q fever, respectively, harbour RCC1 repeat coding genes. Legionella pneumophila secretes the RCC1 repeat 'effector' proteins LegG1, PpgA and PieG into eukaryotic host cells, where they promote the activation of the pleiotropic small GTPase Ran, microtubule stabilisation, pathogen vacuole motility and intracellular bacterial growth as well as host cell migration. The RCC1 repeat effectors localise to the pathogen vacuole or the host plasma membrane and target distinct components of the Ran GTPase cycle, including Ran modulators and the small GTPase itself. Coxiella burnetii translocates the RCC1 repeat effector NopA into host cells, where the protein localises to nucleoli. NopA binds to Ran GTPase and promotes the nuclear accumulation of Ran(GTP), thus pertubing the import of the transcription factor NF-κB and innate immune signalling. Hence, divergent evolution of bacterial RCC1 repeat effectors defines the range of Ran GTPase cycle targets and likely allows fine-tuning of Ran GTPase activation by the pathogens at different cellular sites.

Intracellular parasitism, the driving force of evolution of Legionella pneumophila and the genus Legionella.

Legionella pneumophila is an intracellular pathogen that causes a severe pneumonia called Legionnaires' disease that is often fatal when not promptly diagnosed and treated. However, L. pneumophila is mainly an environmental pathogen of protozoa. This bacterium parasitizes free-living amoeba and other aquatic protozoa with which it co-evolved over an evolutionary long time. Due to the close relationship between hosts and pathogens, their co-evolution leads to molecular interactions such as the exchange of genetic material through horizontal gene transfer (HGT). Those genes that confer an advantage to the bacteria were fixed in their genomes and help these pathogens to subvert host functions to their advantage. Genome sequencing of L. pneumophila and recently of the entire genus Legionella that comprises over 60 species revealed that Legionellae have co-opted genes and thus cellular functions from their eukaryotic hosts to a surprisingly high extent never observed before for an prokaryotic organism. Acquisition and loss of these eukaryotic-like genes and eukaryotic domains is an ongoing process underlining the highly dynamic nature of the Legionella genomes. Although the large amount and diversity of HGT that occurred between Legionella and their protozoan hosts seems to be unique in the prokaryotic world, the analyses of more and more genomes from environmental organisms and symbionts of amoeba revealed that such genetic exchanges occur among all amoeba-associated bacteria and also among the different microorganisms that infect amoeba such as viruses. This dynamic reshuffling and gene-acquisition has led to the emergence of major human pathogens such as Legionella and may lead to the emergence of new human pathogens from the environment.

The pleiotropic Legionella transcription factor LvbR links the Lqs and c-di-GMP regulatory networks to control biofilm architecture and virulence.

The causative agent of Legionnaires' disease, Legionella pneumophila, colonizes amoebae and biofilms in the environment. The opportunistic pathogen employs the Lqs (Legionella quorum sensing) system and the signalling molecule LAI-1 (Legionella autoinducer-1) to regulate virulence, motility, natural competence and expression of a 133 kb genomic "fitness island", including a putative novel regulator. Here, we show that the regulator termed LvbR is an LqsS-regulated transcription factor that binds to the promoter of lpg1056/hnox1 (encoding an inhibitor of the diguanylate cyclase Lpg1057), and thus, regulates proteins involved in c-di-GMP metabolism. LvbR determines biofilm architecture, since L. pneumophila lacking lvbR accumulates less sessile biomass and forms homogeneous mat-like structures, while the parental strain develops more compact bacterial aggregates. Comparative transcriptomics of sessile and planktonic ΔlvbR or ΔlqsR mutant strains revealed concerted (virulence, fitness island, metabolism) and reciprocally (motility) regulated genes in biofilm and broth respectively. Moreover, ΔlvbR is hyper-competent for DNA uptake, defective for phagocyte infection, outcompeted by the parental strain in amoebae co-infections and impaired for cell migration inhibition. Taken together, our results indicate that L. pneumophila LvbR is a novel pleiotropic transcription factor, which links the Lqs and c-di-GMP regulatory networks to control biofilm architecture and pathogen-host cell interactions.

Multiple major disease-associated clones of Legionella pneumophila have emerged recently and independently.

Legionella pneumophila is an environmental bacterium and the leading cause of Legionnaires' disease. Just five sequence types (ST), from more than 2000 currently described, cause nearly half of disease cases in northwest Europe. Here, we report the sequence and analyses of 364 L. pneumophila genomes, including 337 from the five disease-associated STs and 27 representative of the species diversity. Phylogenetic analyses revealed that the five STs have independent origins within a highly diverse species. The number of de novo mutations is extremely low with maximum pairwise single-nucleotide polymorphisms (SNPs) ranging from 19 (ST47) to 127 (ST1), which suggests emergences within the last century. Isolates sampled geographically far apart differ by only a few SNPs, demonstrating rapid dissemination. These five STs have been recombining recently, leading to a shared pool of allelic variants potentially contributing to their increased disease propensity. The oldest clone, ST1, has spread globally; between 1940 and 2000, four new clones have emerged in Europe, which show long-distance, rapid dispersal. That a large proportion of clinical cases is caused by recently emerged and internationally dispersed clones, linked by convergent evolution, is surprising for an environmental bacterium traditionally considered to be an opportunistic pathogen. To simultaneously explain recent emergence, rapid spread and increased disease association, we hypothesize that these STs have adapted to new man-made environmental niches, which may be linked by human infection and transmission.

Targeting of RNA Polymerase II by a nuclear Legionella pneumophila Dot/Icm effector SnpL.

The intracellular pathogen Legionella pneumophila influences numerous eukaryotic cellular processes through the Dot/Icm-dependent translocation of more than 300 effector proteins into the host cell. Although many translocated effectors localise to the Legionella replicative vacuole, other effectors can affect remote intracellular sites. Following infection, a subset of effector proteins localises to the nucleus where they subvert host cell transcriptional responses to infection. Here, we identified Lpw27461 (Lpp2587), Lpg2519 as a new nuclear-localised effector that we have termed SnpL. Upon ectopic expression or during L. pneumophila infection, SnpL showed strong nuclear localisation by immunofluorescence microscopy but was excluded from nucleoli. Using immunoprecipitation and mass spectrometry, we determined the host-binding partner of SnpL as the eukaryotic transcription elongation factor, Suppressor of Ty5 (SUPT5H)/Spt5. SUPT5H is an evolutionarily conserved component of the DRB sensitivity-inducing factor complex that regulates RNA Polymerase II dependent mRNA processing and transcription elongation. Protein interaction studies showed that SnpL bound to the central Kyprides, Ouzounis, Woese motif region of SUPT5H. Ectopic expression of SnpL led to massive upregulation of host gene expression and macrophage cell death. The activity of SnpL further highlights the ability of L. pneumophila to control fundamental eukaryotic processes such as transcription that, in the case of SnpL, leads to global upregulation of host gene expression.

Biological Diversity and Evolution of Type IV Secretion Systems.

The bacterial type IV secretion systems (T4SSs) are a highly functionally and structurally diverse superfamily of secretion systems found in many species of Gram-negative and -positive bacteria. Collectively, the T4SSs can translocate DNA and monomeric and multimeric protein substrates to a variety of bacterial and eukaryotic cell types. Detailed phylogenomics analyses have established that the T4SSs evolved from ancient conjugation machines whose original functions were to disseminate mobile DNA elements within and between bacterial species. How members of the T4SS superfamily evolved to recognize and translocate specific substrate repertoires to prokaryotic or eukaryotic target cells is a fascinating question from evolutionary, biological, and structural perspectives. In this chapter, we will summarize recent findings that have shaped our current view of the biological diversity of the T4SSs. We focus mainly on two subtypes, designated as the types IVA (T4ASS) and IVB (T4BSS) systems that respectively are represented by the paradigmatic Agrobacterium tumefaciens VirB/VirD4 and Legionella pneumophila Dot/Icm T4SSs. We present current information about the composition and architectures of these representative systems. We also describe how these and a few related T4ASS and T4BSS members evolved as specialized nanomachines through acquisition of novel domains or subunits, a process that ultimately generated extensive genetic and structural mosaicism among this secretion superfamily. Finally, we present new phylogenomics information establishing that the T4BSSs are much more broadly distributed than initially envisioned.

Bacterial remodelling of the host epigenome: functional role and evolution of effectors methylating host histones.

The modulation of the chromatin organization of eukaryotic cells plays an important role in regulating key cellular processes including host defence mechanisms against pathogens. Thus, to successfully survive in a host cell, a sophisticated bacterial strategy is the subversion of nuclear processes of the eukaryotic cell. Indeed, the number of bacterial proteins that target host chromatin to remodel the host epigenetic machinery is expanding. Some of the identified bacterial effectors that target the chromatin machinery are 'eukaryotic-like' proteins as they mimic eukaryotic histone writers in carrying the same enzymatic activities. The best-studied examples are the SET domain proteins that methylate histones to change the chromatin landscape. In this review, we will discuss SET domain proteins identified in the Legionella, Chlamydia and Bacillus genomes that encode enzymatic activities targeting host histones. Moreover, we discuss their possible origin as having evolved from prokaryotic ancestors or having been acquired from their eukaryotic hosts during their co-evolution. The characterization of such bacterial effectors as modifiers of the host chromatin landscape is an exciting field of research as it elucidates new bacterial strategies to not only manipulate host functions through histone modifications but it may also identify new modifications of the mammalian host cells not known before.

The Legionella pneumophila kai operon is implicated in stress response and confers fitness in competitive environments.

Legionella pneumophila uses aquatic protozoa as replication niche and protection from harsh environments. Although L. pneumophila is not known to have a circadian clock, it encodes homologues of the KaiBC proteins of Cyanobacteria that regulate circadian gene expression. We show that L. pneumophila kaiB, kaiC and the downstream gene lpp1114, are transcribed as a unit under the control of the stress sigma factor RpoS. KaiC and KaiB of L. pneumophila do not interact as evidenced by yeast and bacterial two-hybrid analyses. Fusion of the C-terminal residues of cyanobacterial KaiB to Legionella KaiB restores their interaction. In contrast, KaiC of L. pneumophila conserved autophosphorylation activity, but KaiB does not trigger the dephosphorylation of KaiC like in Cyanobacteria. The crystal structure of L. pneumophila KaiB suggests that it is an oxidoreductase-like protein with a typical thioredoxin fold. Indeed, mutant analyses revealed that the kai operon-encoded proteins increase fitness of L. pneumophila in competitive environments, and confer higher resistance to oxidative and sodium stress. The phylogenetic analysis indicates that L. pneumophila KaiBC resemble Synechosystis KaiC2B2 and not circadian KaiB1C1. Thus, the L. pneumophila Kai proteins do not encode a circadian clock, but enhance stress resistance and adaption to changes in the environments.

From amoeba to macrophages: exploring the molecular mechanisms of Legionella pneumophila infection in both hosts.

Legionella pneumophila is a Gram-negative bacterium and the causative agent of Legionnaires' disease. It replicates within amoeba and infects accidentally human macrophages. Several similarities are seen in the L. pneumophila-infection cycle in both hosts, suggesting that the tools necessary for macrophage infection may have evolved during co-evolution of L. pneumophila and amoeba. The establishment of the Legionella-containing vacuole (LCV) within the host cytoplasm requires the remodeling of the LCV surface and the hijacking of vesicles and organelles. Then L. pneumophila replicates in a safe intracellular niche in amoeba and macrophages. In this review we will summarize the existing knowledge of the L. pneumophila infection cycle in both hosts at the molecular level and compare the factors involved within amoeba and macrophages. This knowledge will be discussed in the light of recent findings from the Acanthamoeba castellanii genome analyses suggesting the existence of a primitive immune-like system in amoeba.

Exchanged cations and water during reactions in polypyrrole macroions from artificial muscles.

The movement of the bilayer (polypyrrole-dodecylbenzenesulfonate/tape) during artificial muscle bending under flow of current square waves was studied in aqueous solutions of chloride salts. During current flow, polypyrrole redox reactions result in variations in the volumes of the films and macroscopic bending: swelling by reduction with expulsion of cations and shrinking by oxidation with the insertion of cations. The described angles follow a linear function, different in each of the studied salts, of the consumed charge: they are faradaic polymeric muscles. The linearity indicates that cations are the only exchanged ions in the studied potential range. By flow of the same specific charge in every electrolyte, different angles were described by the muscle. The charge and the angle allow the number and volume of both the exchanged cations and the water molecules (related to a reference) between the film to be determined, in addition to the electrolyte per unit of charge during the driving reaction. The attained apparent solvation numbers for the exchanged cations were: 0.8, 0.7, 0.6, 0.5, 0.5, 0.4, 0.25, and 0.0 for Na(+), Mg(2+), La(3+), Li(+), Ca(2+), K(+), Rb(+), and Cs(+), respectively.

Facile Synthesis of Carbon-Based Inks to Develop Metal-Free ORR Electrocatalysts for Electro-Fenton Removal of Amoxicillin.

The electro-Fenton process is based on the generation of hydroxyl radicals (OH•) from hydroxide peroxide (H2O2) generated in situ by an oxygen reduction reaction (ORR). Catalysts based on carbon gels have aroused the interest of researchers as ORR catalysts due to their textural, chemical and even electrical properties. In this work, we synthesized metal-free electrocatalysts based on carbon gels doped with graphene oxide, which were conformed to a working electrode. The catalysts were prepared from organic-gel-based inks using painted (brush) and screen-printed methods free of binders. These new methods of electrode preparation were compared with the conventional pasted method on graphite supports using a binder. All these materials were tested for the electro-Fenton degradation of amoxicillin using a homemade magnetite coated with carbon (Fe3O4/C) as a Fenton catalyst. All catalysts showed very good behavior, but the one prepared by ink painting (brush) was the best one. The degradation of amoxicillin was close to 90% under optimal conditions ([Fe3O4/C] = 100 mg L-1, -0.55 V) with the catalyst prepared using the painted method with a brush, which had 14.59 mA cm-2 as JK and a H2O2 electrogeneration close to 100% at the optimal voltage. These results show that carbon-gel-based electrocatalysts are not only very good at this type of application but can be adhered to graphite free of binders, thus enhancing all their catalytic properties.

Characterization of an acetyltransferase that detoxifies aromatic chemicals in Legionella pneumophila.

Legionella pneumophila is an opportunistic pathogen and the causative agent of Legionnaires' disease. Despite being exposed to many chemical compounds in its natural and man-made habitats (natural aquatic biotopes and man-made water systems), L. pneumophila is able to adapt and survive in these environments. The molecular mechanisms by which this bacterium detoxifies these chemicals remain poorly understood. In particular, the expression and functions of XMEs (xenobiotic-metabolizing enzymes) that could contribute to chemical detoxification in L. pneumophila have been poorly documented at the molecular and functional levels. In the present paper we report the identification and biochemical and functional characterization of a unique acetyltransferase that metabolizes aromatic amine chemicals in three characterized clinical strains of L. pneumophila (Paris, Lens and Philadelphia). Strain-specific sequence variations in this enzyme, an atypical member of the arylamine N-acetyltransferase family (EC 2.3.1.5), produce enzymatic variants with different structural and catalytic properties. Functional inactivation and complementation experiments showed that this acetyltransferase allows L. pneumophila to detoxify aromatic amine chemicals and grow in their presence. The present study provides a new enzymatic mechanism by which the opportunistic pathogen L. pneumophila biotransforms and detoxifies toxic aromatic chemicals. These data also emphasize the role of XMEs in the environmental adaptation of certain prokaryotes.

Analysis of the Legionella longbeachae genome and transcriptome uncovers unique strategies to cause Legionnaires' disease.

Legionella pneumophila and L. longbeachae are two species of a large genus of bacteria that are ubiquitous in nature. L. pneumophila is mainly found in natural and artificial water circuits while L. longbeachae is mainly present in soil. Under the appropriate conditions both species are human pathogens, capable of causing a severe form of pneumonia termed Legionnaires' disease. Here we report the sequencing and analysis of four L. longbeachae genomes, one complete genome sequence of L. longbeachae strain NSW150 serogroup (Sg) 1, and three draft genome sequences another belonging to Sg1 and two to Sg2. The genome organization and gene content of the four L. longbeachae genomes are highly conserved, indicating strong pressure for niche adaptation. Analysis and comparison of L. longbeachae strain NSW150 with L. pneumophila revealed common but also unexpected features specific to this pathogen. The interaction with host cells shows distinct features from L. pneumophila, as L. longbeachae possesses a unique repertoire of putative Dot/Icm type IV secretion system substrates, eukaryotic-like and eukaryotic domain proteins, and encodes additional secretion systems. However, analysis of the ability of a dotA mutant of L. longbeachae NSW150 to replicate in the Acanthamoeba castellanii and in a mouse lung infection model showed that the Dot/Icm type IV secretion system is also essential for the virulence of L. longbeachae. In contrast to L. pneumophila, L. longbeachae does not encode flagella, thereby providing a possible explanation for differences in mouse susceptibility to infection between the two pathogens. Furthermore, transcriptome analysis revealed that L. longbeachae has a less pronounced biphasic life cycle as compared to L. pneumophila, and genome analysis and electron microscopy suggested that L. longbeachae is encapsulated. These species-specific differences may account for the different environmental niches and disease epidemiology of these two Legionella species.

The SET and ankyrin domains of the secreted Legionella pneumophila histone methyltransferase work together to modify host chromatin.

IMPORTANCE: Legionella pneumophila is an intracellular bacterium responsible of Legionnaires' disease, a severe pneumonia that is often fatal when not treated promptly. The pathogen's ability to efficiently colonize the host resides in its ability to replicate intracellularly. Essential for intracellular replication is translocation of many different protein effectors via a specialized secretion system. One of them, called RomA, binds and directly modifies the host chromatin at a unique site (tri-methylation of lysine 14 of histone H3 [H3K14me]). However, the molecular mechanisms of binding are not known. Here, we resolve this question through structural characterization of RomA together with the H3 peptide. We specifically reveal an active role of the ankyrin repeats located in its C-terminal in the interaction with the histone H3 tail. Indeed, without the ankyrin domains, RomA loses its ability to act as histone methyltransferase. These results discover the molecular mechanisms by which a bacterial histone methyltransferase that is conserved in L. pneumophila strains acts to modify chromatin.

Structural basis for the toxicity of Legionella pneumophila effector SidH.

Legionella pneumophila (LP) secretes more than 300 effectors into the host cytosol to facilitate intracellular replication. One of these effectors, SidH, 253 kDa in size with no sequence similarity to proteins of known function is toxic when overexpressed in host cells. SidH is regulated by the LP metaeffector LubX which targets SidH for degradation in a temporal manner during LP infection. The mechanism underlying the toxicity of SidH and its role in LP infection are unknown. Here, we determined the cryo-EM structure of SidH at 2.7 Å revealing a unique alpha helical arrangement with no overall similarity to known protein structures. Surprisingly, purified SidH came bound to a E. coli EF-Tu/t-RNA/GTP ternary complex which could be modeled into the cryo-EM density. Mutation of residues disrupting the SidH-tRNA interface and SidH-EF-Tu interface abolish the toxicity of overexpressed SidH in human cells, a phenotype confirmed in infection of Acanthamoeba castellani. We also present the cryo-EM structure of SidH in complex with a U-box domain containing ubiquitin ligase LubX delineating the mechanism of regulation of SidH. Our data provide the basis for the toxicity of SidH and into its regulation by the metaeffector LubX.

The evolution and role of eukaryotic-like domains in environmental intracellular bacteria: the battle with a eukaryotic cell.

Intracellular pathogens that are able to thrive in different environments, such as Legionella spp. that preferentially live in protozoa in aquatic environments or environmental Chlamydiae that replicate either within protozoa or a range of animals, possess a plethora of cellular biology tools to influence their eukaryotic host. The host manipulation tools that evolved in the interaction with protozoa confer these bacteria the capacity to also infect phylogenetically distinct eukaryotic cells, such as macrophages, and thus they can also be human pathogens. To manipulate the host cell, bacteria use protein secretion systems and molecular effectors. Although these molecular effectors are encoded in bacteria, they are expressed and function in a eukaryotic context often mimicking or inhibiting eukaryotic proteins. Indeed, many of these effectors have eukaryotic-like domains. In this review, we propose that the main pathways that environmental intracellular bacteria need to subvert in order to establish the host eukaryotic cell as a replication niche are chromatin remodelling, ubiquitination signalling and modulation of protein-protein interactions via tandem repeat domains. We then provide mechanistic insight into how these proteins might have evolved. Finally, we highlight that in environmental intracellular bacteria the number of eukaryotic-like domains and proteins is considerably higher than in intracellular bacteria specialized to an isolated niche, such as obligate intracellular human pathogens. As mimics of eukaryotic proteins are critical components of host-pathogen interactions, this distribution of eukaryotic-like domains suggests that the environment has selected them.

Bacterial methyltransferases: from targeting bacterial genomes to host epigenetics.

Methyltransferase (MTases) enzymes transfer methyl groups particularly on proteins and nucleotides, thereby participating in controlling the epigenetic information in both prokaryotes and eukaryotes. The concept of epigenetic regulation by DNA methylation has been extensively described for eukaryotes. However, recent studies have extended this concept to bacteria showing that DNA methylation can also exert epigenetic control on bacterial phenotypes. Indeed, the addition of epigenetic information to nucleotide sequences confers adaptive traits including virulence-related characteristics to bacterial cells. In eukaryotes, an additional layer of epigenetic regulation is obtained by post-translational modifications of histone proteins. Interestingly, in the last decades it was shown that bacterial MTases, besides playing an important role in epigenetic regulations at the microbe level by exerting an epigenetic control on their own gene expression, are also important players in host-microbe interactions. Indeed, secreted nucleomodulins, bacterial effectors that target the nucleus of infected cells, have been shown to directly modify the epigenetic landscape of the host. A subclass of nucleomodulins encodes MTase activities, targeting both host DNA and histone proteins, leading to important transcriptional changes in the host cell. In this review, we will focus on lysine and arginine MTases of bacteria and their hosts. The identification and characterization of these enzymes will help to fight bacterial pathogens as they may emerge as promising targets for the development of novel epigenetic inhibitors in both bacteria and the host cells they infect.

Genomic erosion and horizontal gene transfer shape functional differences of the ExlA toxin in Pseudomonas spp.

Two-partner secretion (TPS) is widespread in the bacterial world. The pore-forming TPS toxin ExlA of Pseudomonas aeruginosa is conserved in pathogenic and environmental Pseudomonas. While P. chlororaphis and P. entomophila displayed ExlA-dependent killing, P. putida did not cause damage to eukaryotic cells. ExlA proteins interacted with epithelial cell membranes; however, only ExlA Pch induced the cleavage of the adhesive molecule E-cadherin. ExlA proteins participated in insecticidal activity toward the larvae of Galleria mellonella and the fly Drosophila melanogaster. Evolutionary analyses demonstrated that the differences in the C-terminal domains are partly due to horizontal movements of the operon within the genus Pseudomonas. Reconstruction of the evolutionary history revealed the complex horizontal acquisitions. Together, our results provide evidence that conserved TPS toxins in environmental Pseudomonas play a role in bacteria-insect interactions and discrete differences in CTDs may determine their specificity and mode of action toward eukaryotic cells.