Host-Microbe Interactions
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Host-Microbe Interactions
Symbionts, pathogens, and everything in between
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BMC Microbiology | Full text | Extensive remodeling of the Pseudomonas syringae pv. avellanae type III secretome associated with two independent host shifts onto hazelnut

Hazelnut (Corylus avellana) decline disease in Greece and Italy is caused by the convergent evolution of two distantly related lineages of Pseudomonas syringae pv. avellanae (Pav).

 

Conclusions
These data show that divergent lineages of P. syringae can converge on identical disease etiology on the same host plant using different virulence mechanisms and that dramatic shifts in the arsenal of T3SEs can accompany disease emergence.

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Root Hairs Play a Key Role in the Endophytic Colonization of Olive Roots by Pseudomonas spp. with Biocontrol Activity

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PLoS Pathogens: Experimental Evolution of Legionella pneumophila in Mouse Macrophages Leads to Strains with Altered Determinants of Environmental Survival

PLoS Pathogens: Experimental Evolution of Legionella pneumophila in Mouse Macrophages Leads to Strains with Altered Determinants of Environmental Survival | Host-Microbe Interactions | Scoop.it
Legionella pneumophila is an accidental pathogen of humans, responsible for the severe, often-fatal pneumonia known as Legionnaires' disease. In the environment, L. pneumophila survives and replicates within protozoa by co-opting the intracellular machinery of these microbial predators. These freshwater encounters between bacteria and protozoa likely provided L. pneumophila with the selective pressures required to evolve into an intracellular pathogen. Many of the host pathways that L. pneumophila manipulates during infection are highly conserved and this is presumably what allows L. pneumophila to infect human cells. It is likely that L. pneumophila is suboptimally adapted to replication within mammalian cells, however, as replication within human cells is thought to be an evolutionary dead end. In this study, we developed an experimental evolution approach to determine what unique selective pressures might be present within mammalian hosts and how these pressures might modify this pathogen. We subjected L. pneumophila to continuous passage within mouse macrophages for several months, selecting for spontaneous mutations that resulted in improved fitness within these cells. We sequenced the genomes of each of the adapted strains, measured the population dynamics of each evolving population, and identified mutations that improve replication in mammalian cells and alter bacterial fitness in amoebae.
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A novel extracellular metallopeptidase domain share... [PLoS One. 2012] - PubMed - NCBI

The mucosal microbiota is recognised as an important factor for our health, with many disease states linked to imbalances in the normal community structure. Hence, there is considerable interest in identifying the molecular basis of human-microbe interactions. In this work we investigated the capacity of microbes to thrive on mucosal surfaces, either as mutualists, commensals or pathogens, using comparative genomics to identify co-occurring molecular traits. We identified a novel domain we named M60-like/PF13402 (new Pfam entry PF13402), which was detected mainly among proteins from animal host mucosa-associated prokaryotic and eukaryotic microbes ranging from mutualists to pathogens. Lateral gene transfers between distantly related microbes explained their shared M60-like/PF13402 domain. The novel domain is characterised by a zinc-metallopeptidase-like motif and is distantly related to known viral enhancin zinc-metallopeptidases. Signal peptides and/or cell surface anchoring features were detected in most microbial M60-like/PF13402 domain-containing proteins, indicating that these proteins target an extracellular substrate. A significant subset of these putative peptidases was further characterised by the presence of associated domains belonging to carbohydrate-binding module family 5/12, 32 and 51 and other glycan-binding domains, suggesting that these novel proteases are targeted to complex glycoproteins such as mucins. An in vitro mucinase assay demonstrated degradation of mammalian mucins by a recombinant form of an M60-like/PF13402-containing protein from the gut mutualist Bacteroides thetaiotaomicron. This study reveals that M60-like domains are peptidases targeting host glycoproteins. These peptidases likely play an important role in successful colonisation of both vertebrate mucosal surfaces and the invertebrate digestive tract by both mutualistic and pathogenic microbes. Moreover, 141 entries across various peptidase families described in the MEROPS database were also identified with carbohydrate-binding modules defining a new functional context for these glycan-binding domains and providing opportunities to engineer proteases targeting specific glycoproteins for both biomedical and industrial applications.
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Symbionticism: Is the microbiome part of the organism or part of the environment?

Symbionticism: Is the microbiome part of the organism or part of the environment? | Host-Microbe Interactions | Scoop.it

One of the central questions in the science of the microbiome is whether an animal’s genes or diet determine the composition of gut bacteria. This debate gets murky very quickly as it raises the fascinating question of whether you should consider your gut bacteria a part of you, just like the genes on your chromosomes in your gut cells, or a part of the environment that affects you, like a fruit that provides you nutrition on a daily basis or a parasite that occasionally makes you sick.

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Trends in Plant Science - The rhizosphere microbiome and plant health

The diversity of microbes associated with plant roots is enormous, in the order of tens of thousands of species. This complex plant-associated microbial community, also referred to as the second genome of the plant, is crucial for plant health. Recent advances in plant–microbe interactions research revealed that plants are able to shape their rhizosphere microbiome, as evidenced by the fact that different plant species host specific microbial communities when grown on the same soil. In this review, we discuss evidence that upon pathogen or insect attack, plants are able to recruit protective microorganisms, and enhance microbial activity to suppress pathogens in the rhizosphere. A comprehensive understanding of the mechanisms that govern selection and activity of microbial communities by plant roots will provide new opportunities to increase crop production.

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Smaller Questions: Symbiosis: Lighting up the world

Smaller Questions: Symbiosis: Lighting up the world | Host-Microbe Interactions | Scoop.it
It is horizontal transmission, or from the hitchhikers of the sea, but how to the squid get the right bacteria to colonize them? Luckily for the bobtailed squid, V. fisheri is the only luminous bacterium that is symbiotically competent, ...
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Lets Talk: A Story of Interspecies Communication : Tomorrow's Table

Lets Talk: A Story of Interspecies Communication : Tomorrow's Table | Host-Microbe Interactions | Scoop.it


Awesome article by Pamela Ronald, Professor of Plant Pathology at the University of California, Davis, discussing new findings on the Ax21 signaling molecule in bacteria, and its detection by plants.

"In a feat worthy of the Turing cryptographers, some plants have evolved a cypher-breaking detection system, called the XA21 receptor, that intercept the bacterial code and use this information to trigger a robust immune response, preventing disease."

 

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BMC Evolutionary Biology | Full text | Diversifying selection and host adaptation in two endosymbiont genomes

The endosymbiont Wolbachia pipientis infects a broad range of arthropod and filarial nematode hosts. These diverse associations form an attractive model for understanding host:symbiont coevolution.
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Lipooligosaccharide is required for... [Proc Natl Acad Sci U S A. 2011] - PubMed - NCBI

Lipopolysaccharides (LPS) and lipooligosaccharides (LOS) are the main lipid components of bacterial outer membranes and are essential for cell viability in most Gram-negative bacteria. Here we show that small molecule inhibitors of LpxC [UDP-3-O-(R-3-hydroxymyristoyl)-GlcNAc deacetylase], the enzyme that catalyzes the first committed step in the biosynthesis of lipid A, block the synthesis of LOS in the obligate intracellular bacterial pathogen Chlamydia trachomatis. In the absence of LOS, Chlamydia remains viable and establishes a pathogenic vacuole ("inclusion") that supports robust bacterial replication. However, bacteria grown under these conditions were no longer infectious. ..These findings suggest the presence of an outer membrane quality control system that regulates Chlamydia developmental transition to infectious elementary bodies and highlights the potential application of LpxC inhibitors as unique class of antichlamydial agents.

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ScienceDirect - Microbes and Infection : When oxygen runs short: the microenvironment drives host-pathogen interactions

Pathogens that colonize or infect the human body have to face varying oxygen concentrations within different organs. Inflammation itself promotes oxygen consumption within affected tissues and creates a low oxygen environment. As a consequence, pathogens and the host immune system have to adapt to rapid changes in oxygen availability. Here we summarize recent findings on the adaptation of pathogens, host defense mechanisms and treatment strategies against intracellular pathogens in a low oxygen environment.

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Instant Evolution in Whiteflies: Just Add Bacteria | College of Agriculture and Life Sciences

Instant Evolution in Whiteflies: Just Add Bacteria | College of Agriculture and Life Sciences | Host-Microbe Interactions | Scoop.it

In just six years, bacteria in the genus Rickettsia spread through a population of the sweet potato whitefly (Bemisia tabaci), an invasive pest of global importance. Infected insects lay more eggs, develop faster and are more likely to survive to adulthood compared to their uninfected peers. The discoveries were made by a University of Arizona-led team of scientists and are published in the April 8 issue of Science.

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Evolutionary transitions in bacterial symbiosis

Diverse bacterial lineages form beneficial infections with eukaryotic hosts. The origins, evolution, and breakdown of these mutualisms represent important evolutionary transitions. To examine these key events, we synthesize data from diverse interactions between bacteria and eukaryote hosts. Five evolutionary transitions are investigated, including the origins of bacterial associations with eukaryotes, the origins and subsequent stable maintenance of bacterial mutualism with hosts, the capture of beneficial symbionts via the evolution of strict vertical transmission within host lineages, and the evolutionary breakdown of bacterial mutualism. Each of these transitions has occurred many times in the history of bacterial–eukaryote symbiosis. We investigate these evolutionary events across the bacterial domain and also among a focal set of well studied bacterial mutualist lineages. Subsequently, we generate a framework for examining evolutionary transitions in bacterial symbiosis and test hypotheses about the selective, ecological, and genomic forces that shape these events.

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Lifestyle transitions in plant pathogenic Colletotrichum fungi deciphered by genome and transcriptome analyses : Nature Genetics : Nature Publishing Group

Lifestyle transitions in plant pathogenic Colletotrichum fungi deciphered by genome and transcriptome analyses : Nature Genetics : Nature Publishing Group | Host-Microbe Interactions | Scoop.it

Colletotrichum species are fungal pathogens that devastate crop plants worldwide. Host infection involves the differentiation of specialized cell types that are associated with penetration, growth inside living host cells (biotrophy) and tissue destruction (necrotrophy). We report here genome and transcriptome analyses of Colletotrichum higginsianum infecting Arabidopsis thaliana and Colletotrichum graminicola infecting maize. Comparative genomics showed that both fungi have large sets of pathogenicity-related genes, but families of genes encoding secreted effectors, pectin-degrading enzymes, secondary metabolism enzymes, transporters and peptidases are expanded in C. higginsianum. Genome-wide expression profiling revealed that these genes are transcribed in successive waves that are linked to pathogenic transitions: effectors and secondary metabolism enzymes are induced before penetration and during biotrophy, whereas most hydrolases and transporters are upregulated later, at the switch to necrotrophy. Our findings show that preinvasion perception of plant-derived signals substantially reprograms fungal gene expression and indicate previously unknown functions for particular fungal cell types.

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Endofungal bacterium controls its host by an hrp type... [ISME J. 2011] - PubMed - NCBI

Burkholderia rhizoxinica and Rhizopus microsporus form a unique symbiosis in which intracellular bacteria produce the virulence factor of the phytopathogenic fungus. Notably, the host strictly requires endobacteria to sporulate. In this study, we show that the endofungal bacteria possess a type III secretion system (T3SS), which has a crucial role in the maintenance of the alliance. Mutants defective in type III secretion show reduced intracellular survival and fail to elicit sporulation of the host. Furthermore, genes coding for T3SS components are upregulated during cocultivation of the bacterial symbiont with their host. This is the first report on a T3SS involved in bacterial-fungal symbiosis. Phylogenetic analysis revealed that the T3SS represents a prototype of a clade of yet uncharacterized T3SSs within the hrp superfamily of T3SSs from plant pathogenic microorganisms. In a control experiment, we demonstrate that under laboratory conditions, rhizoxin production was not required for establishment of the symbiotic interaction.

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Frontiers | Understanding the Role of Host Hemocytes in a Squid/Vibrio Symbiosis Using Transcriptomics and Proteomics | Frontiers in Molecular Innate Immunity

Frontiers | Understanding the Role of Host Hemocytes in a Squid/Vibrio Symbiosis Using Transcriptomics and Proteomics | Frontiers in Molecular Innate Immunity | Host-Microbe Interactions | Scoop.it
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PLoS ONE: Selection of Salmonella enterica Serovar Typhi Genes Involved during Interaction with Human Macrophages by Screening of a Transposon Mutant Library

PLoS ONE: Selection of Salmonella enterica Serovar Typhi Genes Involved during Interaction with Human Macrophages by Screening of a Transposon Mutant Library | Host-Microbe Interactions | Scoop.it

The human-adapted Salmonella enterica serovar Typhi (S. Typhi) causes a systemic infection known as typhoid fever. This disease relies on the ability of the bacterium to survive within macrophages. In order to identify genes involved during interaction with macrophages, a pool of approximately 105 transposon mutants of S. Typhi was subjected to three serial passages of 24 hours through human macrophages. Mutants recovered from infected macrophages (output) were compared to the initial pool (input) and those significantly underrepresented resulted in the identification of 130 genes encoding for cell membrane components, fimbriae, flagella, regulatory processes, pathogenesis, and many genes of unknown function. Defined deletions in 28 genes or gene clusters were created and mutants were evaluated in competitive and individual infection assays for uptake and intracellular survival during interaction with human macrophages. Overall, 26 mutants had defects in the competitive assay and 14 mutants had defects in the individual assay. Twelve mutants had defects in both assays, including acrA, exbDB, flhCD, fliC, gppA, mlc, pgtE, typA, waaQGP, SPI-4, STY1867-68, and STY2346. The complementation of several mutants by expression of plasmid-borne wild-type genes or gene clusters reversed defects, confirming that the phenotypic impairments within macrophages were gene-specific. In this study, 35 novel phenotypes of either uptake or intracellular survival in macrophages were associated with Salmonella genes. Moreover, these results reveal several genes encoding molecular mechanisms not previously known to be involved in systemic infection by human-adapted typhoidal Salmonella that will need to be elucidated.

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ScienceDirect.com - Current Opinion in Microbiology - The genome biology of phytoplasma: modulators of plants and insects

ScienceDirect.com - Current Opinion in Microbiology - The genome biology of phytoplasma: modulators of plants and insects | Host-Microbe Interactions | Scoop.it

Phytoplasmas are bacterial pathogens of plants that are transmitted by insects. These bacteria uniquely multiply intracellularly in both plants (Plantae) and insects (Animalia). Similarly to bacterial endosymbionts, phytoplasmas have reduced genomes with limited metabolic capabilities. Nonetheless, the chromosomes of many phytoplasmas are rich in repeated DNA consisting of mobile elements. Phytoplasmas produce an arsenal of effectors most of which are encoded on these mobile elements and on plasmids. These effectors target conserved plant transcription factors resulting in witches’ broom and leafy flower symptoms and suppression of plant defense to insect vectors that transmit the phytoplasmas. Future studies of these fascinating microbes will generate a wealth of new knowledge about forces that shape genomes and microbial interactions with multicellular hosts

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PLoS Pathogens: Endophytic Life Strategies Decoded by Genome and Transcriptome Analyses of the Mutualistic Root Symbiont Piriformospora indica

PLoS Pathogens: Endophytic Life Strategies Decoded by Genome and Transcriptome Analyses of the Mutualistic Root Symbiont Piriformospora indica | Host-Microbe Interactions | Scoop.it

 Cytological evidence for biotrophic growth followed by a cell death-associated phase that results in a mutually beneficial outcome, supports the idea that P. indica represents a missing link between decomposer fungi and obligate biotrophic mutualists.

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PLoS Biology: Protection of Sinorhizobium against Host Cysteine-Rich Antimicrobial Peptides Is Critical for Symbiosis

PLoS Biology: Protection of Sinorhizobium against Host Cysteine-Rich Antimicrobial Peptides Is Critical for Symbiosis | Host-Microbe Interactions | Scoop.it

Certain bacterial species have the unique capacity to enter into eukaryotic host cells and establish prolonged infections, which can be beneficial (e.g. bacterial-legume symbiosis) or detrimental (e.g. chronic disease) for the host. However, the mechanisms by which bacteria persist in host cells are poorly understood. Legume peptides and the bacterial BacA membrane protein play essential roles in enabling bacteria to establish prolonged legume infections. However, the biological function of BacA in persistent legume infections has eluded scientists for nearly two decades. In this article, we investigated a potential relationship between legume peptides and BacA in the establishment of prolonged bacterial-legume infections. We found that BacA was critical to protect bacteria against the antimicrobial action of legume peptides, thereby allowing the peptides to induce bacterial persistence within the legume rather than rapid bacterial death. Mammalian hosts also produce peptides in response to invading microorganisms and BacA proteins are critical for medically important bacterial pathogens such as Mycobacterium tuberculosis to form prolonged mammalian infections. Therefore, our results suggest that BacA-mediated protection against host peptides might be a conserved mechanism used by both symbiotic and pathogenic bacterial species to establish long-term host infections.

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The transcriptome of the arbuscular mycorrhizal f... [New Phytol. 2011] - PubMed - NCBI

The arbuscular mycorrhizal symbiosis is arguably the most ecologically important eukaryotic symbiosis, yet it is poorly understood at the molecular level. To provide novel insights into the molecular basis of symbiosis-associated traits, we report the first genome-wide analysis of the transcriptome from Glomus intraradices DAOM 197198...

We identified transcripts coding for the meiotic recombination machinery, as well as meiosis-specific proteins, suggesting that the lack of a known sexual cycle in G. intraradices is not a result of major deletions of genes essential for sexual reproduction and meiosis. Induced expression of genes encoding membrane transporters and small secreted proteins in intraradical mycelium, together with the lack of expression of hydrolytic enzymes acting on plant cell wall polysaccharides, are all features of G. intraradices that are shared with ectomycorrhizal symbionts and obligate biotrophic pathogens.

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Conversion of Commensal Escherichia coli K-12 to an Invasive Form via Expression of a Mutant Histone-Like Protein

IMPORTANCE Escherichia coli K-12 is well established as a benign laboratory strain and a human intestinal commensal. Recent evidences, however, indicate that the typical noninvasive nature of resident E. coli can be reversed under specific circumstances even in the absence of any major genomic flux. We previously engineered an E. coli strain with a mutant histone-like protein, HU, which exhibited significant changes in nucleoid organization and global transcription. Here we showed that the changes induced by the mutant HU have critical functional consequences: from a strict extracellular existence, the mutant E. coli adopts an almost obligate intracellular lifestyle. The internalized E. coli exhibits many of the prototypical characteristics of traditional intracellular bacteria, like phagosomal escape, intracellular replication, and subversion of host cell apoptosis. We suggest that E. coli K-12 can switch between widely divergent lifestyles in relation to mammalian host cells by reprogramming its cellular transcription program and without gross changes in its genomic content.

 

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Surface-Affinity Profiling To Identify Host-Pathogen Interactions

 Here, we aimed to identify host receptor proteins by introducing a preincubation step in which bacterial cells were first allowed to capture human proteins from epithelial cell lysates. Using Streptococcus gallolyticus as a model bacterium, liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of proteolytically released peptides yielded the identification of a selective number of human epithelial proteins that were retained by the bacterial surface. Of these potential receptors for bacterial interference, (cyto)keratin-8 (CK8) was verified as the most significant hit, and its surface localization was investigated by subcellular fractionation and confocal microscopy. Interestingly, bacterial enolase could be assigned as an interaction partner of CK8 by MS/MS analysis of cross-linked protein complexes and complementary immunoblotting experiments. As surface-exposed enolase has a proposed role in epithelial adherence of several Gram-positive pathogens, its interaction with CK8 seems to point toward a more general virulence mechanism. In conclusion, our study shows that surface-affinity profiling is a valuable tool to identify novel adhesin-receptor pairs, which advocates its application in other hybrid biological systems.

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Horizontal transmission of the insect symbiont... [Proc Biol Sci. 2011] - PubMed - NCBI

Plants can serve as a reservoir for horizontal transmission of Rickettsia, a mechanism which may explain the occurrence of phylogenetically similar symbionts among unrelated phytophagous insect species.

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PLoS Genetics: The Evolution of Host Specialization in the Vertebrate Gut Symbiont Lactobacillus reuteri

PLoS Genetics: The Evolution of Host Specialization in the Vertebrate Gut Symbiont Lactobacillus reuteri | Host-Microbe Interactions | Scoop.it

The study revealed divergent patterns of genome evolution in rodent and human lineages and a distinct genome inventory in host-restricted sub-populations of L. reuteri that reflected the niche characteristics in the gut of their particular vertebrate hosts. The ecological significance of representative rodent-specific genes was demonstrated in gnotobiotic mice. In conclusion, this work provided evidence that the vertebrate gut symbiont Lactobacillus reuteri, despite the likelihood of horizontal transmission, has remained stably associated with related groups of vertebrate hosts over evolutionary time and has evolved a lifestyle specialized to these host animals.

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