Host Responses to the Pathogen Mycobacterium avium subsp. paratuberculosis and Beneficial Microbes Exhibit Host Sex Specificity

Differences between microbial pathogenesis in male and female hosts are well characterized in disease conditions connected to sexual transmission. However, limited biological insight is available on variances attributed to sex specificity in host-microbe interactions, and it is most often a minimized variable outside these transmission events. In this work, we studied two gut microbes—a pathogen, Mycobacterium avium subsp. paratuberculosis, and a probiotic, Lactobacillus animalis NP-51—and the interaction between each agent and the male and female gastrointestinal systems. This trial was conducted in BALB/c mice (n = 5 per experimental group and per sex at a given time point), with analysis at four time points over 180 days. Host responses to M. avium subsp. paratuberculosis and L. animalis were sensitive to sex. Cytokines that were significantly different (P ≤ 0.05) between the sexes included interleukin-1α/β (IL-1α/β), IL-17, IL-6, IL-10, IL-12, and gamma interferon (IFN-γ) and were dependent on experimental conditions. However, granulocyte-macrophage colony-stimulating factor (GM-CSF), vascular endothelial growth factor (VEGF), and IL-13/23 showed no sex specificity. A metabolomics study indicated a 0.5- to 2.0-fold (log₂ scale) increase in short-chain fatty acids (butyrate and acetate) in males and greater increases in o-phosphocholine or histidine from female colon tissues; variances distinct to each sex were observed with age or long-term probiotic consumption. Two genera, Staphylococcus and Roseburia, were consistently overrepresented in females compared to males; other species were specific to one sex but fluctuated depending on experimental conditions. The differences observed suggest that male and female gut tissues and microbiota respond to newly introduced microorganisms differently and that gut-associated microorganisms with host immune system responses and metabolic activity are supported by biology distinct to the host sex.     

Evolution of Pathogen Specialisation in a Host Metapopulation: Joint Effects of Host and Pathogen Dispersal

Metapopulation processes are important determinants of epidemiological and evolutionary dynamics in host-pathogen systems, and are therefore central to explaining observed patterns of disease or genetic diversity. In particular, the spatial scale of interactions between pathogens and their hosts is of primary importance because migration rates of one species can affect both spatial and temporal heterogeneity of selection on the other. In this study we developed a stochastic and discrete time simulation model to specifically examine the joint effects of host and pathogen dispersal on the evolution of pathogen specialisation in a spatially explicit metapopulation. We consider a plant-pathogen system in which the host metapopulation is composed of two plant genotypes. The pathogen is dispersed by air-borne spores on the host metapopulation. The pathogen population is characterised by a single life-history trait under selection, the infection efficacy. We found that restricted host dispersal can lead to high amount of pathogen diversity and that the extent of pathogen specialisation varied according to the spatial scale of host-pathogen dispersal. We also discuss the role of population asynchrony in determining pathogen evolutionary outcomes.     

Chlamydiae Assemble a Pathogen Synapse to Hijack the Host Endoplasmic Reticulum

Chlamydiae are obligate intracellular bacterial pathogens that replicate within a specialized membrane‐bound compartment, termed an ‘inclusion’. The inclusion membrane is a critical host–pathogen interface, yet the extent of its interaction with cellular organelles and the origin of this membrane remain poorly defined. Here we show that the host endoplasmic reticulum (ER) is specifically recruited to the inclusion, and that key rough ER (rER) proteins are enriched on and translocated into the inclusion. rER recruitment is a Chlamydia‐orchestrated process that occurs independently of host trafficking. Generation of infectious progeny requires an intact ER, since ER vacuolation early during infection stalls inclusion development, whereas disruption post ER recruitment bursts the inclusion. Electron tomography and immunolabelling of Chlamydia‐infected cells reveal ‘pathogen synapses’ at which ordered arrays of chlamydial type III secretion complexes connect to the inclusion membrane only at rER contact sites. Our data show a supramolecular assembly involved in pathogen hijack of a key host organelle.     

Riboflavin-induced Priming for Pathogen Defense in Arabidopsis thaliana

Riboflavin (vitamin B2) participates in a variety of redox processes that affect plant defense responses. Previously we have shown that riboflavin induces pathogen resistance in the absence of hypersensitive cell death (HCD) in plants. Herein, we report that riboflavin induces priming of defense responses in Arabidopsis thaliana toward infection by virulent Pseudomonas syringae pv. Tomato DC3000 (Pst). Induced resistance was mechanistically connected with the expression of defense response genes and cellular defense events, including H2O2 burst, HCD, and callose deposition in the plant. Riboflavin treatment and inoculation of plants with Pst were neither active but both synergized to induce defense responses. The priming process needed NPR1 (essential regulator of systemic acquired resistance) and maintenance of H2O2 burst but was independent of salicylic acid, jasmonic acid, ethylene, and abscisic acid. Our results suggest that the role of riboflavin in priming defenses is subject to a signaling process distinct from the known pathways of hormone signal transduction.     

Riboflavin-induced Priming for Pathogen Defense in Arabidopsis thaliana

Riboflavin （vitamin B2） participates in a variety of redox processes that affect plant defense responses. Previously we have shown that riboflavin induces pathogen resistance in the absence of hypersensitive cell death （HCD） in plants. Herein, we report that riboflavin induces priming of defense responses in Arabidopsis thaliana toward infection by virulent Pseudomonas syringae pv. tomato DC3000 （Pst）. Induced resistance was mechanistically connected with the expression of defense response genes and cellular defense events, including H202 burst, HCD, and callose deposition in the plant. Riboflavin treatment and inoculation of plants with Pst were neither active but both synergized to induce defense responses. The priming process needed NPRI （essential regulator of systemic acquired resistance） and maintenance of H202 burst but was independent of salicylic acid, jasmonic acid, ethylene, and abscisic acid. Our results suggest that the role of riboflavin in priming defenses is subject to a signaling process distinct from the known pathways of hormone signal transduction.     

Vector-Borne Pathogen and Host Evolution in a Structured Immuno-Epidemiological System

Vector-borne disease transmission is a common dissemination mode used by many pathogens to spread in a host population. Similar to directly transmitted diseases, the within-host interaction of a vector-borne pathogen and a host’s immune system influences the pathogen’s transmission potential between hosts via vectors. Yet there are few theoretical studies on virulence–transmission trade-offs and evolution in vector-borne pathogen–host systems. Here, we consider an immuno-epidemiological model that links the within-host dynamics to between-host circulation of a vector-borne disease. On the immunological scale, the model mimics antibody-pathogen dynamics for arbovirus diseases, such as Rift Valley fever and West Nile virus. The within-host dynamics govern transmission and host mortality and recovery in an age-since-infection structured host-vector-borne pathogen epidemic model. By considering multiple pathogen strains and multiple competing host populations differing in their within-host replication rate and immune response parameters, respectively, we derive evolutionary optimization principles for both pathogen and host. Invasion analysis shows that the \({\mathcal {R}}_0\) maximization principle holds for the vector-borne pathogen. For the host, we prove that evolution favors minimizing case fatality ratio (CFR). These results are utilized to compute host and pathogen evolutionary trajectories and to determine how model parameters affect evolution outcomes. We find that increasing the vector inoculum size increases the pathogen \({\mathcal {R}}_0\), but can either increase or decrease the pathogen virulence (the host CFR), suggesting that vector inoculum size can contribute to virulence of vector-borne diseases in distinct ways.     

Airborne Induction and Priming of Plant Defenses against a Bacterial Pathogen

Herbivore-induced plant volatiles affect the systemic response of plants to local damage and hence represent potential plant hormones. These signals can also lead to “plant-plant communication,” a defense induction in yet undamaged plants growing close to damaged neighbors. We observed this phenomenon in the context of disease resistance. Lima bean (Phaseolus lunatus) plants in a natural population became more resistant against a bacterial pathogen, Pseudomonas syringae pv syringae, when located close to conspecific neighbors in which systemic acquired resistance to pathogens had been chemically induced with benzothiadiazole (BTH). Airborne disease resistance induction could also be triggered biologically by infection with avirulent P. syringae. Challenge inoculation after exposure to induced and noninduced plants revealed that the air coming from induced plants mainly primed resistance, since expression of PATHOGENESIS-RELATED PROTEIN2 (PR-2) was significantly stronger in exposed than in nonexposed individuals when the plants were subsequently challenged by P. syringae. Among others, the plant-derived volatile nonanal was present in the headspace of BTH-treated plants and significantly enhanced PR-2 expression in the exposed plants, resulting in reduced symptom appearance. Negative effects on growth of BTH-treated plants, which usually occur as a consequence of the high costs of direct resistance induction, were not observed in volatile organic compound-exposed plants. Volatile-mediated priming appears to be a highly attractive means for the tailoring of systemic acquired resistance against plant pathogens.Plants respond to attack by pathogens or herbivores with extensive changes in gene expression that lead to induced resistance phenomena (Karban and Baldwin, 1997); various traits are then expressed de novo or at much higher intensities, which reduce or prevent further tissue damage. As both pathogens and herbivores can spread from the initial site of attack to other organs, such plant responses are often not restricted to the damaged tissue but are expressed systemically, in yet undamaged organs. Three plant hormones playing central roles in the long-distance signaling that underlies this systemic response to local attack are jasmonic acid (JA), ethylene, and salicylic acid (SA). SA and JA, in particular, are transported themselves or in the form of derivatives within the plant in order to elicit systemic responses (Truman et al., 2007; Wasternack, 2007; Heil and Ton, 2008).Recent studies have revealed that long-distance signaling is not only caused by molecules that are transported in the vascular system; signals can also be volatile compounds that move in the headspace outside the plant (Heil and Ton, 2008). In particular, green-leaf volatiles and other herbivore-induced volatile organic compounds (VOCs) can mediate the systemic response of plants to local herbivore damage (Karban et al., 2006; Frost et al., 2007; Heil and Silva Bueno, 2007). Since such VOCs move freely in the air, they may also affect neighboring plants and then mediate the phenomenon of “plant-plant communication,” which has been found in taxonomically unrelated plants such as Arabidopsis (Arabidopsis thaliana), alder (Alnus glutinosa), corn (Zea mays), lima bean (Phaseolus lunatus), maple (Acer saccharum), sagebrush (Artemisia tridentata), and wild tobacco (Nicotiana attenuata; Baldwin and Schultz, 1983; Rhoades, 1983; Tscharntke et al., 2001; Engelberth et al., 2004; Heil and Kost, 2006; Karban et al., 2006; Paschold et al., 2006; Heil and Silva Bueno, 2007; Ton et al., 2007; Godard et al., 2008).Plant-plant communication via VOCs thus appears to be a common phenomenon in herbivore resistance, and similar volatile compounds can also mediate the beneficial effects that are caused by plant growth-promoting rhizobacteria (Ryu et al., 2003, 2004b). Furthermore, exposure to VOCs such as trans-2-hexenal, cis-3-hexenal, or cis-3-hexenol enhanced resistance of Arabidopsis against the fungal pathogen Botrytis cinerea (Kishimoto et al., 2005), which indicates that VOCs may also induce disease resistance. However, the wound response, the induction of VOCs, the effects of plant growth-promoting rhizobacteria, and even the resistance to necrotrophic pathogens such as B. cinerea and Alternaria brassiccicola are mediated via JA signaling (Wasternack and Parthier, 1997; Pieterse et al., 1998; Schilmiller and Howe, 2005; Francia et al., 2007; Heil, 2008; Heil and Ton, 2008). In contrast, systemic acquired resistance (SAR) to biotrophic pathogens in many plant species is mediated by SA signaling, which increases the expression of phytoalexins and of several PATHOGENESIS-RELATED (PR) proteins (van Loon, 1997; Hammerschmidt and Smith-Becker, 1999; Durrant and Dong, 2004) and which usually is thought to act as an antagonist to JA signaling (Maleck et al., 2000; Pieterse and Dicke, 2007; Korneef and Pieterse, 2008). The volatile derivative of SA, methyl salicylate (MeSA), has been proposed as the most likely systemic signal (Park et al., 2007). In tobacco (Nicotiana tabacum), MeSA is converted back to SA, which then forms the active resistance-inducing compound (Kumar and Klessig, 2003; Forouhar et al., 2005). This mechanism might underlie the resistance induction in tobacco plants that were exposed to high MeSA concentrations (Shulaev et al., 1997). In a study on the role of MeSA as a mobile signal, Park and coworkers (2007), however, only found evidence for the vascular transport of this compound.We used lima bean to investigate whether plant-plant signaling can also affect SAR to biotrophic bacterial pathogens. Plants were exposed to the VOCs emitted from neighbors that had been treated with the chemical SAR elicitor benzothiadiazole [BTH; benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester] or that had been induced biologically, and resulting changes in resistance were monitored at the phenotypic and gene expression levels. A common phenomenon involved in disease resistance is priming, which prepares the plant to respond more rapidly and/or effectively to subsequent attack (van Hulten et al., 2006; Bruce et al., 2007; Goellner and Conrath, 2008) but which comes at much lower costs than direct resistance induction (Heil and Baldwin, 2002; Walters and Boyle, 2005; Walters and Heil, 2007). Therefore, we investigated whether VOCs also can prime resistance to pathogens by first exposing plants to VOCs coming from directly induced plants and then challenging them with Pseudomonas syringae pv syringae. Finally, VOCs released from induced plants were analyzed, and the most likely candidates were evaluated for their effect on expression of the resistance marker gene PR-2 in order to understand the chemical nature of the signal.     

Host Responses to Intestinal Microbial Antigens in Gluten-Sensitive Mice

Background and Aims

Excessive uptake of commensal bacterial antigens through a permeable intestinal barrier may influence host responses to specific antigen in a genetically predisposed host. The aim of this study was to investigate whether intestinal barrier dysfunction induced by indomethacin treatment affects the host response to intestinal microbiota in gluten-sensitized HLA-DQ8/HCD4 mice.

Methodology/Principal Findings

HLA-DQ8/HCD4 mice were sensitized with gluten, and gavaged with indomethacin plus gluten. Intestinal permeability was assessed by Ussing chamber; epithelial cell (EC) ultra-structure by electron microscopy; RNA expression of genes coding for junctional proteins by Q-real-time PCR; immune response by in-vitro antigen-specific T-cell proliferation and cytokine analysis by cytometric bead array; intestinal microbiota by fluorescence in situ hybridization and analysis of systemic antibodies against intestinal microbiota by surface staining of live bacteria with serum followed by FACS analysis. Indomethacin led to a more pronounced increase in intestinal permeability in gluten-sensitized mice. These changes were accompanied by severe EC damage, decreased E-cadherin RNA level, elevated IFN-γ in splenocyte culture supernatant, and production of significant IgM antibody against intestinal microbiota.

Conclusion

Indomethacin potentiates barrier dysfunction and EC injury induced by gluten, affects systemic IFN-γ production and the host response to intestinal microbiota antigens in HLA-DQ8/HCD4 mice. The results suggest that environmental factors that alter the intestinal barrier may predispose individuals to an increased susceptibility to gluten through a bystander immune activation to intestinal microbiota.     

The Social Biology of Quorum Sensing in a Naturalistic Host Pathogen System

1. Download : Download high-res image (395KB)
2. Download : Download full-size image

     

Pathogen Host Switching in Commercial Trade with Management Recommendations

Global wildlife trade exacerbates the spread of nonindigenous species. Pathogens also move with hosts through trade and often are released into naïve populations with unpredictable outcomes. Amphibians are moved commercially for pets, food, bait, and biomedicine, and are an excellent model for studying how wildlife trade relates to pathogen pollution. Ranaviruses are amphibian pathogens associated with annual population die-offs; multiple strains of tiger salamander ranaviruses move through the bait trade in the western United States. Ranaviruses infect amphibians, reptiles, and fish and are of additional concern because they can switch hosts. Tiger salamanders are used as live bait for freshwater fishing and are a potential source for ranaviruses switching hosts from amphibians to fish. We experimentally injected largemouth bass with a bait trade tiger salamander ranavirus. Largemouth bass became infected but exhibited no signs of disease or mortality. Amphibian bait ranaviruses have the potential to switch hosts to infect fish, but fish may act as dead-end hosts or nonsymptomatic carriers, potentially spreading infection as a result of trade.     

Transcriptomic and Proteomic Analyses of Resistant Host Responses in Arachis diogoi Challenged with Late Leaf Spot Pathogen,Phaeoisariopsis personata

Late leaf spot is a serious disease of peanut caused by the imperfect fungus, Phaeoisariopsis personata. Wild diploid species, Arachis diogoi. is reported to be highly resistant to this disease and asymptomatic. The objective of this study is to investigate the molecular responses of the wild peanut challenged with the late leaf spot pathogen using cDNA-AFLP and 2D proteomic study. A total of 233 reliable, differentially expressed genes were identified in Arachis diogoi. About one third of the TDFs exhibit no significant similarity with the known sequences in the data bases. Expressed sequence tag data showed that the characterized genes are involved in conferring resistance in the wild peanut to the pathogen challenge. Several genes for proteins involved in cell wall strengthening, hypersensitive cell death and resistance related proteins have been identified. Genes identified for other proteins appear to function in metabolism, signal transduction and defence. Nineteen TDFs based on the homology analysis of genes associated with defence, signal transduction and metabolism were further validated by quantitative real time PCR (qRT-PCR) analyses in resistant wild species in comparison with a susceptible peanut genotype in time course experiments. The proteins corresponding to six TDFs were differentially expressed at protein level also. Differentially expressed TDFs and proteins in wild peanut indicate its defence mechanism upon pathogen challenge and provide initial breakthrough of genes possibly involved in recognition events and early signalling responses to combat the pathogen through subsequent development of resistivity. This is the first attempt to elucidate the molecular basis of the response of the resistant genotype to the late leaf spot pathogen, and its defence mechanism.     

Population Dynamics of Sugar Beets, Rhizoctonia solani, and Laetisaria arvalis: Responses of a Host, Plant Pathogen, and Hyperparasite to Perturbation in the Field

Rhizoctonia solani causes crown rot of sugar beets, a severe disease that has destroyed up to 60% of the plants in a test field in western Nebraska. Laetisaria arvalis, a natural hyperparasite of Rhizoctonia spp., was isolated from fields in western Nebraska. To test for the potential for biological control of R. solani, in November 1980 (following harvest) we applied various combinations of a nematicide (Telone II; Dow Chemical Co.), a nutrition source (sugar beet pulp), and an inoculum of L. arvalis in a randomized block design. Populations of R. solani, L. arvalis, and sugar beets were monitored monthly through October 1981 (just after harvest). In control and nematicide plots, the R. solani population did not change significantly through time. In plots inoculated with L. arvalis, the R. solani populations declined through March, concomitant with an increase in L. arvalis. L. arvalis then declined with a corresponding increase in the R. solani populations. Beet plant numbers declined significantly in all treatments. We suggest that reduction of the R. solani populations with the hyperparasite L. arvalis is possible but that a stable equilibrium naturally exists.