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

The perfluorooctanoic acid accumulation and release from pipelines promoted growth of bacterial communities and opportunistic pathogens with different antibiotic resistance genes in drinking water

The spread of opportunistic pathogens (OPs) and antibiotic resistance genes (ARGs) through drinking water has already caused serious human health issues. There is also an urgent need to know the effects of perfluorooctanoic acid (PFOA) on OPs with different ARGs in drinking water. Our results suggested that PFOA accumulation and release from the pipelines induced its concentration in pipelines effluents increase from 0.03 ± 0.01 μg/L to 0.70 ± 0.01 μg/L after 6 months accumulation. The PFOA also promoted the growth of Hyphomicrobium, Microbacterium, and Bradyrhizobium. In addition, PFOA accumulation and release from the pipelines enhanced the metabolism and tricarboxylic acid (TCA) cycle processes, resulting in more extracellular polymeric substances (EPS) production. Due to EPS protection, Pseudomonas aeruginosa and Legionella pneumophila increased to (7.20 ± 0.09) × 104 gene copies/mL, and (8.85 ± 0.11) × 102 gene copies/mL, respectively. Moreover, PFOA also enhanced the transfer potential of different ARGs, including emrB, mdtB, mdtC, mexF, and macB. The main bacterial community composition and the main OPs positively correlated with the main ARGs and mobile genetic elements (MGE)-ARGs significantly. Therefore, PFOA promoted the propagation of OPs with different ARGs. These results are meaningful for controlling the microbial risk caused by the OPs with ARGs and MGE-ARGs in drinking water.

Addictive manipulation: a perspective on the role of reproductive parasitism in the evolution of bacteria-eukaryote symbioses

Wolbachia bacteria encompass noteworthy reproductive manipulators of their arthropod hosts. which influence host reproduction to favour their own transmission, also exploiting toxin-antitoxin systems. Recently, multiple other bacterial symbionts of arthropods have been shown to display comparable manipulative capabilities. Here, we wonder whether such phenomena are truly restricted to arthropod hosts. We focused on protists, primary models for evolutionary investigations on eukaryotes due to their diversity and antiquity, but still overall under-investigated. After a thorough re-examination of the literature on bacterial-protist interactions with this question in mind, we conclude that such bacterial 'addictive manipulators' of protists do exist, are probably widespread, and have been overlooked until now as a consequence of the fact that investigations are commonly host-centred, thus ineffective to detect such behaviour. Additionally, we posit that toxin-antitoxin systems are crucial in these phenomena of addictive manipulation of protists, as a result of recurrent evolutionary repurposing. This indicates intriguing functional analogy and molecular homology with plasmid-bacterial interplays. Finally, we remark that multiple addictive manipulators are affiliated with specific bacterial lineages with ancient associations with diverse eukaryotes. This suggests a possible role of addictive manipulation of protists in paving the way to the evolution of bacteria associated with multicellular organisms.

Host-bacteria interactions: ecological and evolutionary insights from ancient, professional endosymbionts

Interactions between eukaryotic hosts and their bacterial symbionts drive key ecological and evolutionary processes, from regulating ecosystems to the evolution of complex molecular machines and processes. Over time, endosymbionts generally evolve reduced genomes, and their relationship with their host tends to stabilize. However, host-bacteria relationships may be heavily influenced by environmental changes. Here, we review these effects on one of the most ancient and diverse endosymbiotic groups, formed by-among others-Legionellales, Francisellaceae, and Piscirickettsiaceae. This group is referred to as Deep-branching Intracellular Gammaproteobacteria (DIG), whose last common ancestor presumably emerged about 2 Ga ago. We show that DIGs are globally distributed, but generally at very low abundance, and are mainly identified in aquatic biomes. Most DIGs harbour a type IVB secretion system, critical for host-adaptation, but its structure and composition vary. Finally, we review the different types of microbial interactions that can occur in diverse environments, with direct or indirect effects on DIG populations. The increased use of omics technologies on environmental samples will allow a better understanding of host-bacterial interactions and help unravel the definition of DIGs as a group from an ecological, molecular, and evolutionary perspective.

Tools and mechanisms of vacuolar escape leading to host egress in Legionella pneumophila infection: Emphasis on bacterial phospholipases

The phenomenon of host cell escape exhibited by intracellular pathogens is a remarkably versatile occurrence, capable of unfolding through lytic or non-lytic pathways. Among these pathogens, the bacterium Legionella pneumophila stands out, having adopted a diverse spectrum of strategies to disengage from their host cells. A pivotal juncture that predates most of these host cell escape modalities is the initial escape from the intracellular compartment. This critical step is increasingly supported by evidence suggesting the involvement of several secreted pathogen effectors, including lytic proteins. In this intricate landscape, L. pneumophila emerges as a focal point for research, particularly concerning secreted phospholipases. While nestled within its replicative vacuole, the bacterium deftly employs both its type II (Lsp) and type IVB (Dot/Icm) secretion systems to convey phospholipases into either the phagosomal lumen or the host cell cytoplasm. Its repertoire encompasses numerous phospholipases A (PLA), including three enzymes-PlaA, PlaC, and PlaD-bearing the GDSL motif. Additionally, there are 11 patatin-like phospholipases A as well as PlaB. Furthermore, the bacterium harbors three extracellular phospholipases C (PLCs) and one phospholipase D. Within this comprehensive review, we undertake an exploration of the pivotal role played by phospholipases in the broader context of phagosomal and host cell egress. Moreover, we embark on a detailed journey to unravel the established and potential functions of the secreted phospholipases of L. pneumophila in orchestrating this indispensable process.

Cross-family small GTPase ubiquitination by the intracellular pathogen Legionella pneumophila

The intracellular bacterial pathogen Legionella pneumophila (L.p.) manipulates eukaryotic host ubiquitination machinery to form its replicative vacuole. While nearly 10% of L.p.'s ∼330 secreted effector proteins are ubiquitin ligases or deubiquitinases, a comprehensive measure of temporally resolved changes in the endogenous host ubiquitinome during infection has not been undertaken. To elucidate how L.p. hijacks host cell ubiquitin signaling, we generated a proteome-wide analysis of changes in protein ubiquitination during infection. We discover that L.p. infection increases ubiquitination of host regulators of subcellular trafficking and membrane dynamics, most notably ∼40% of mammalian Ras superfamily small GTPases. We determine that these small GTPases undergo nondegradative ubiquitination at the Legionella-containing vacuole (LCV) membrane. Finally, we find that the bacterial effectors SidC/SdcA play a central role in cross-family small GTPase ubiquitination, and that these effectors function upstream of SidE family ligases in the polyubiquitination and retention of GTPases in the LCV membrane. This work highlights the extensive reconfiguration of host ubiquitin signaling by bacterial effectors during infection and establishes simultaneous ubiquitination of small GTPases across the Ras superfamily as a novel consequence of L.p. infection. Our findings position L.p. as a tool to better understand how small GTPases can be regulated by ubiquitination in uninfected contexts.

Cross-family small GTPase ubiquitination by the intracellular pathogen Legionella pneumophila

The intracellular bacterial pathogen Legionella pneumophila (L.p.) manipulates eukaryotic host ubiquitination machinery to form its replicative vacuole. While nearly 10% of L.p.'s arsenal of ~330 secreted effector proteins have been biochemically characterized as ubiquitin ligases or deubiquitinases, a comprehensive measure of temporally resolved changes in the endogenous host ubiquitinome during infection has not been undertaken. To elucidate how L.p hijacks ubiquitin signaling within the host cell, we undertook a proteome-wide analysis of changes in protein ubiquitination during infection. We discover that L.p. infection results in increased ubiquitination of host proteins regulating subcellular trafficking and membrane dynamics, most notably 63 of ~160 mammalian Ras superfamily small GTPases. We determine that these small GTPases predominantly undergo non-degradative monoubiquitination, and link ubiquitination to recruitment to the Legionella-containing vacuole membrane. Finally, we find that the bacterial effectors SidC/SdcA play a central, but likely indirect, role in cross-family small GTPase ubiquitination. This work highlights the extensive reconfiguration of host ubiquitin signaling by bacterial effectors during infection and establishes simultaneous ubiquitination of small GTPases across the Ras superfamily as a novel consequence of L.p. infection. This work positions L.p. as a tool to better understand how small GTPases can be regulated by ubiquitination in uninfected contexts.

Crystal structure of the N-terminal domain of the effector protein SidI of Legionella pneumophila reveals a glucosyl transferase domain

The Gram-negative bacterium Legionella pneumophila is an accidental human pathogen that can cause a life-threatening respiratory infection called Legionellosis. In the course of infection, L. pneumophila injects more than 300 effector proteins into the host cell. The effector proteins modify the intracellular environment in order to create a stable compartment for proliferation within the host cell. The effector protein SidI has been shown to potently inhibit host translation upon translocation. SidI is able to interact with the translation elongation factor eEF1A, which has been hypothesized to be a target of SidI. A postulated glycosyltransferase domain in the C-terminal half may be responsible for the toxic effect of SidI. Here, we present the crystal structure of an N-terminal fragment of SidI containing residues 37-573. The structure is divided into three subdomains, two of which display a novel fold. The third subdomain shows close structural homology to GT-B fold glycosyltransferases. Based on structural analysis we predict that the two previously identified residues R453 and E482 assume roles in the catalytic activity of SidI. Furthermore, we show that the N-terminal fragment of SidI is able to directly interact with a postulated target, the translation elongation factor eEF1A.

Genomic characterization and assessment of pathogenic potential of Legionella spp. isolates from environmental monitoring

Several species in the genus Legionella are known to cause an acute pneumonia when the aerosols containing the bacteria from man-made water systems are inhaled. The disease is usually caused by Legionella pneumophila, but other species have been implicated in the infection. The disease is frequently manifested as an outbreak, which means several people are affected when exposed to the common source of Legionella contamination. Therefor environmental surveillance which includes isolation and identification of Legionella is performed routinely. However, usually no molecular or genome-based methods are employed in further characterization of the isolates during routine environmental monitoring. During several years of such monitoring, isolates from different geographical locations were collected and 39 of them were sequenced by hybrid de novo approach utilizing short and long sequencing reads. In addition, the isolates were typed by standard culture and MALDI-TOF method. The sequencing reads were assembled and annotated to produce high-quality genomes. By employing discriminatory genome typing, four potential new species in the Legionella genus were identified, which are yet to be biochemically and morphologically characterized. Moreover, functional annotations concerning virulence and antimicrobial resistance were performed on the sequenced genomes. The study contributes to the knowledge on little-known non-pneumophila species present in man-made water systems and establishes support for future genetic relatedness studies as well as understanding of their pathogenic potential.

Protein sociology of ProA, Mip and other secreted virulence factors at the Legionella pneumophila surface

The pathogenicity of L. pneumophila, the causative agent of Legionnaires' disease, depends on an arsenal of interacting proteins. Here we describe how surface-associated and secreted virulence factors of this pathogen interact with each other or target extra- and intracellular host proteins resulting in host cell manipulation and tissue colonization. Since progress of computational methods like AlphaFold, molecular dynamics simulation, and docking allows to predict, analyze and evaluate experimental proteomic and interactomic data, we describe how the combination of these approaches generated new insights into the multifaceted "protein sociology" of the zinc metalloprotease ProA and the peptidyl-prolyl cis/trans isomerase Mip (macrophage infectivity potentiator). Both virulence factors of L. pneumophila interact with numerous proteins including bacterial flagellin (FlaA) and host collagen, and play important roles in virulence regulation, host tissue degradation and immune evasion. The recent progress in protein-ligand analyses of virulence factors suggests that machine learning will also have a beneficial impact in early stages of drug discovery.

Reduced and Nonreduced Genomes in Paraburkholderia Symbionts of Social Amoebas

The social amoeba Dictyostelium discoideum is a predatory soil protist frequently used for studying host-pathogen interactions. A subset of D. discoideum strains isolated from soil persistently carry symbiotic Paraburkholderia, recently formally described as P. agricolaris, P. bonniea, and P. hayleyella. The three facultative symbiont species of D. discoideum present a unique opportunity to study a naturally occurring symbiosis in a laboratory model protist. There is a large difference in genome size between P. agricolaris (8.7 million base pairs [Mbp]) versus P. hayleyella and P. bonniea (4.1 Mbp). We took a comparative genomics approach and compared the three genomes of D. discoideum symbionts to 12 additional Paraburkholderia genomes to test for genome evolution patterns that frequently accompany host adaptation. Overall, P. agricolaris is difficult to distinguish from other Paraburkholderia based on its genome size and content, but the reduced genomes of P. bonniea and P. hayleyella display characteristics indicative of genome streamlining rather than deterioration during adaptation to their protist hosts. In addition, D. discoideum-symbiont genomes have increased secretion system and motility genes that may mediate interactions with their host. Specifically, adjacent BurBor-like type 3 and T6SS-5-like type 6 secretion system operons shared among all three D. discoideum-symbiont genomes may be important for host interaction. Horizontal transfer of these secretion system operons within the amoeba host environment may have contributed to the unique ability of these symbionts to establish and maintain a symbiotic relationship with D. discoideum. IMPORTANCE Protists are a diverse group of typically single cell eukaryotes. Bacteria and archaea that form long-term symbiotic relationships with protists may evolve in additional ways than those in relationships with multicellular eukaryotes such as plants, animals, or fungi. Social amoebas are a predatory soil protist sometimes found with symbiotic bacteria living inside their cells. They present a unique opportunity to explore a naturally occurring symbiosis in a protist frequently used for studying host-pathogen interactions. We show that one amoeba-symbiont species is similar to other related bacteria in genome size and content, while the two reduced-genome-symbiont species show characteristics of genome streamlining rather than deterioration during adaptation to their host. We also identify sets of genes present in all three amoeba-symbiont genomes that are potentially used for host-symbiont interactions. Because the amoeba symbionts are distantly related, the amoeba host environment may be where these genes were shared among symbionts.

Antimicrobial susceptibility profiles and tentative epidemiological cutoff values of Legionella pneumophila from environmental water and soil sources in China

Legionnaires’ disease (LD), caused by Legionella, including the most prevalent Legionella pneumophila, has been treated primarily with antibiotics. Environmental water and soil are the reservoirs for L. pneumophila. Studying antimicrobial susceptibility using a large number of isolates from various environmental sources and regions could provide an unbiased result. In the present study, antimicrobial susceptibility of 1464 environmental L. pneumophila isolates that were derived from various environmental water and soil sources of 12 cities in China to rifampin (RIF), erythromycin (ERY), clarithromycin (CLA), azithromycin (AZI), ciprofloxacin (CIP), moxifloxacin (MOX), levofloxacin (LEV), and doxycycline (DOX) was investigated, and minimum inhibitory concentration (MIC) data were obtained. We show that regarding macrolides, ERY was least active (MIC₉₀ = 0.5 mg/L), while CLA was most active (MIC₉₀ = 0.063 mg/L). A total of three fluoroquinolones have similar MICs on L. pneumophila. Among these antimicrobials, RIF was the most active agent, while DOX was the most inactive one. We observed different susceptibility profiles between serogroup 1 (sg1) and sg2-15 or between water and soil isolates from different regions. The ECOFFs were ERY and AZI (0.5 mg/L), RIF (0.002 mg/L), CIP, CLA and MOX (0.125 mg/L), LEV (0.063 mg/), and DOX (32 mg/L). Overall, two fluoroquinolone-resistant environmental isolates (0.14%) were first documented based on the wild-type MIC distribution. Not all azithromycin-resistant isolates (44/46, 95.65%) harbored the lpeAB efflux pump. The MICs of the ERY and CLA on the lpeAB + isolates were not elevated. These results suggested that the lpeAB efflux pump might be only responsible for AZI resistance, and undiscovered AZI-specific resistant mechanisms exist in L. pneumophila. Based on the big MIC data obtained in the present study, the same defense strategies, particularly against both CLA and RIF, may exist in L. pneumophila. The results determined in our study will guide further research on antimicrobial resistance mechanisms of L. pneumophila and could be used as a reference for setting clinical breakpoints and discovering antimicrobial-resistant isolates in the clinic, contributing to the antibiotic choice in the treatment of LD.

Presence of Viable, Clinically Relevant Legionella Bacteria in Environmental Water and Soil Sources of China

The distribution of pathogenic Legionella in the environmental soil and water of China has not been documented yet. In this study, Legionella was detected in 129 of 575 water (22.43%) and 41 of 442 soil samples (9.28%) by culture. Twelve Legionella species were identified, of which 11 were disease-associated. Of the Legionella-positive samples, 109 of 129 (84.50%) water and 29 of 41 (70.73%) soil were positive for L. pneumophila, which accounted for about 75% of Legionella isolates in both water and soil, suggesting L. pneumophila was the most frequent species. Soil showed a higher diversity of Legionella spp. as compared with water (0.6279 versus 0.4493). In contrast, serogroup (sg) 1 was more prevalent among L. pneumophila isolates from water than from soil (26.66% versus 12.21%). Moreover, many disease-associated sequence types (STs) of L. pneumophila were found in China. Intragenic recombination was acting on L. pneumophila from both water and soil. Phylogeny, population structure, and molecular evolution analyses revealed a probable existence of L. pneumophila isolates with a special genetic background that is more adaptable to soil or water sources and a small proportion of genetic difference between water and soil isolates. The detection of viable, clinically relevant Legionella demonstrates soil as another source for harboring and dissemination of pathogenic Legionella bacteria in China. Future research should assess the implication in public health with the presence of Legionella in the soil and illustrate the genetic and pathogenicity difference of Legionella between water and soil, particularly the most prevalent L. pneumophila. IMPORTANCE Pathogenic Legionella spp. is the causative agent of Legionnaires' disease (LD), and L. pneumophila is the most common one. Most studies have focused on L. pneumophila from water and clinical samples. However, the soil is another important reservoir for this bacterium, and the distribution of Legionella spp. in water and soil sources has not been compared and documented in China yet. Discovering the distribution of Legionella spp. and L. pneumophila in the two environments may help a deep understanding of the pathogenesis and molecular evolution of the bacterium. Our research systematically uncovered the distributions of Legionella spp. in different regions and sources (e.g., water and soil) of China. Moreover, phylogeny, population structure, and molecular evolution study revealed the possible existence of L. pneumophila with a special genetic background that is more adaptable to soil or water sources, and genetic difference may exist.

Discovering Biological Conflict Systems Through Genome Analysis: Evolutionary Principles and Biochemical Novelty

Biological replicators, from genes within a genome to whole organisms, are locked in conflicts. Comparative genomics has revealed a staggering diversity of molecular armaments and mechanisms regulating their deployment, collectively termed biological conflict systems. These encompass toxins used in inter- and intraspecific interactions, self/nonself discrimination, antiviral immune mechanisms, and counter-host effectors deployed by viruses and intragenomic selfish elements. These systems possess shared syntactical features in their organizational logic and a set of effectors targeting genetic information flow through the Central Dogma, certain membranes, and key molecules like NAD⁺. These principles can be exploited to discover new conflict systems through sensitive computational analyses. This has led to significant advances in our understanding of the biology of these systems and furnished new biotechnological reagents for genome editing, sequencing, and beyond. We discuss these advances using specific examples of toxins, restriction-modification, apoptosis, CRISPR/second messenger-regulated systems, and other enigmatic nucleic acid-targeting systems. Expected final online publication date for the Annual Review of Biomedical Data Science, Volume 5 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Genome analysis of Legionella pneumophila ST23 from various countries reveals highly similar strains

ST23 isolated in Italy are analysed by cgMLST and SNP approaches and they are also compared with ST23 from other countries. They are found to be phylogenetically related independently on year, town, or country of isolation.

Legionella pneumophila serogroup 1 (Lp1) sequence type (ST) 23 is one of the most commonly detected STs in Italy where it currently causes all investigated outbreaks. ST23 has caused both epidemic and sporadic cases between 1995 and 2018 and was analysed at genomic level and compared with ST23 isolated in other countries to determine possible similarities and differences. A core genome multi-locus sequence typing (cgMLST), based on a previously described set of 1,521 core genes, and single-nucleotide polymorphisms (SNPs) approaches were applied to an ST23 collection including genomes from Italy, France, Denmark and Scotland. DNAs were automatically extracted, libraries prepared using NextEra library kit and MiSeq sequencing performed. Overall, 63 among clinical and environmental Italian Lp1 isolates and a further seven and 11 ST23 from Denmark and Scotland, respectively, were sequenced, and pangenome analysed. Both cgMLST and SNPs analyses showed very few loci and SNP variations in ST23 genomes. All the ST23 causing outbreaks and sporadic cases in Italy and elsewhere, were phylogenetically related independent of year, town or country of isolation. Distances among the ST23s were further shortened when SNPs due to horizontal gene transfers were removed. The Lp1 ST23 isolated in Italy have kept their monophyletic origin, but they are phylogenetically close also to ST23 from other countries. The ST23 are quite widespread in Italy, and a thorough epidemiological investigation is compelled to determine sources of infection when this ST is identified in both LD sporadic cases and outbreaks.

Molecular Mimicry: a Paradigm of Host-Microbe Coevolution Illustrated by Legionella

Through coevolution with host cells, microorganisms have acquired mechanisms to avoid the detection by the host surveillance system and to use the cell's supplies to establish themselves. Indeed, certain pathogens have evolved proteins that imitate specific eukaryotic cell proteins, allowing them to manipulate host pathways, a phenomenon termed molecular mimicry. Bacterial "eukaryotic-like proteins" are a remarkable example of molecular mimicry. They are defined as proteins that strongly resemble eukaryotic proteins or that carry domains that are predominantly present in eukaryotes and that are generally absent from prokaryotes. The widest diversity of eukaryotic-like proteins known to date can be found in members of the bacterial genus Legionella, some of which cause a severe pneumonia in humans. The characterization of a number of these proteins shed light on their importance during infection. The subsequent identification of eukaryotic-like genes in the genomes of other amoeba-associated bacteria and bacterial symbionts suggested that eukaryotic-like proteins are a common means of bacterial evasion and communication, shaped by the continuous interactions between bacteria and their protozoan hosts. In this review, we discuss the concept of molecular mimicry using Legionella as an example and show that eukaryotic-like proteins effectively manipulate host cell pathways. The study of the function and evolution of such proteins is an exciting field of research that is leading us toward a better understanding of the complex world of bacterium-host interactions. Ultimately, this knowledge will teach us how host pathways are manipulated and how infections may possibly be tackled.

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.