HOST-PARASITE RELATIONSHIPS AMONG GROUP A STREPTOCOCCI. 3. DEPRESSION OF RETICULOENDOTHELIAL FUNCTION BY STREPTOCOCCAL PYROGENIC EXOTOXINS.
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Hanna, Edgar E. (University of Minnesota, Minneapolis), and Dennis W. Watson. Host-parasite relationships among group A streptococci. III. Depression of reticuloendothelial function by streptococcal pyrogenic exotoxins. J. Bacteriol. 89:154-158. 1965.-Measurement of the rate of clearance of colloidal carbon from the circulating blood is an effective and simple technique for assessing the functional state of the reticuloendothelial system (RES) of experimental animals. This paper concerns a study of the RES function in rabbits after treatment with streptococcal pyrogenic exotoxins. Intravenous injection of 1.0 ml of the toxin produced by a strain of type 18, group A streptococcus caused a prolonged (at least 24 hr) depression of RES function. The activity at 48 hr after toxin injection was about equal to that in control animals. Repeated intravenous injections of the toxin abolished the initial depressing effect on RES function, but did not cause stimulation. In comparison, intravenous injection of equivalent doses of endotoxin prepared from Escherichia coli COO8 also caused an initial depression of RES function; however, in contrast with the effect of exotoxin, stimulation occurred as early as 24 hr and was about twice as active at 48 hr. The prolonged depression by streptococcal pyrogenic exotoxin is suggested as one means by which this toxin potentiates lethality and tissue damage by other toxins such as streptolysin O and endotoxins from gram-negative bacteria. (+info)
The paradox of the parasites: implications for biological invasion.
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The enemy-release hypothesis for biological invasions supposes that invasive species may be more successful in their introduced ranges than in their native ranges owing to the absence of coevolved natural enemies. Recent studies supporting this hypothesis have found that introduced plants and animals are less parasitized in their introduced ranges than in their native ranges. Expanding on this theory, I hypothesize that the role of enemy release may differ among the introduction, establishment and spread phases of an invasion. I present a simple model indicating that parasite release is unlikely to greatly affect the chance of establishment in populations with and without an immune subpopulation. The specific numerical relationship between the number of individuals introduced and the chance of establishment depends on a relationship between virulence, here conceptualized as the chance for the extinction of a lineage, and the fraction of the population infected at introduction. These results support the idea of a 'filter effect' in which different biological processes regulate the different phases of an invasion. (+info)
Cleaner wrasse prefer client mucus: support for partner control mechanisms in cleaning interactions.
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Recent studies on cleaning behaviour suggest that there are conflicts between cleaners and their clients over what cleaners eat. The diet of cleaners usually contains ectoparasites and some client tissue. It is unclear, however, whether cleaners prefer client tissue over ectoparasites or whether they include client tissue in their diet only when searching for parasites alone is not profitable. To distinguish between these two hypotheses, we trained cleaner fish Labroides dimidiatus to feed from plates and offered them client mucus from the parrotfish Chlorurus sordidus, parasitic monogenean flatworms, parasitic gnathiid isopods and boiled flour glue as a control. We found that cleaners ate more mucus and monogeneans than gnathiids, with gnathiids eaten slightly more often than the control substance. Because gnathiids are the most abundant ectoparasites, our results suggest a potential for conflict between cleaners and clients over what the cleaner should eat, and support studies emphasizing the importance of partner control in keeping cleaning interactions mutualistic. (+info)
Nematode.net: a tool for navigating sequences from parasitic and free-living nematodes.
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Nematode.net (www.nematode.net) is a web- accessible resource for investigating gene sequences from nematode genomes. The database is an outgrowth of the parasitic nematode EST project at Washington University's Genome Sequencing Center (GSC), St Louis. A sister project at the University of Edinburgh and the Sanger Institute is also underway. More than 295,000 ESTs have been generated from >30 nematodes other than Caenorhabditis elegans including key parasites of humans, animals and plants. Nematode.net currently provides NemaGene EST cluster consensus sequence, enhanced online BLAST search tools, functional classifications of cluster sequences and comprehensive information concerning the ongoing generation of nematode genome data. The long-term goal of nematode.net is to provide the scientific community with the highest quality sequence information and tools for studying these diverse species. (+info)
NEMBASE: a resource for parasitic nematode ESTs.
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NEMBASE (available at http://www.nematodes.org) is a publicly available online database providing access to the sequence and associated meta-data currently being generated as part of the Edinburgh-Wellcome Trust Sanger Institute parasitic nematode EST project. NEMBASE currently holds approximately 100 000 sequences from 10 different species of nematode. To facilitate ease of use, sequences have been processed to generate a non-redundant set of gene objects ('partial genome') for each species. Users may query the database on the basis of BLAST annotation, sequence similarity or expression profiles. NEMBASE also features an interactive Java-based tool (SimiTri) which allows the simultaneous display and analysis of the relative similarity relationships of groups of sequences to three different databases. NEMBASE is currently being expanded to include sequence data from other nematode species. Other developments include access to accurate peptide predictions, improved functional annotation and incorporation of automated processes allowing rapid analysis of nematode-specific gene families. (+info)
Structural insight into arginine degradation by arginine deiminase, an antibacterial and parasite drug target.
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l-Arginine deiminase (ADI) catalyzes the irreversible hydrolysis of arginine to citrulline and ammonia. ADI is involved in the first step of the most widespread anaerobic route of arginine degradation. ADI, missing in high eukaryotes, is a potential antimicrobial and antiparasitic drug target. We have determined the crystal structure of ADI from Pseudomonas aeruginosa by the multi-wavelength anomalous diffraction method at 2.45 A resolution. The structure exhibits similarity to other arginine-modifying or substituted arginine-modifying enzymes such as dimethylarginine dimethylaminohydrolase (DDAH), arginine:glycine amidinotransferase, and arginine:inosamine-phosphate amidinotransferase, despite the lack of significant amino acid sequence homology to these enzymes. The similarity spans a core domain comprising five betabetaalphabeta motifs arranged in a circle around a 5-fold pseudosymmetry axis. ADI contains an additional alpha-helical domain of novel topology inserted between the first and the second betabetaalphabeta modules. A catalytic triad, Cys-His-Glu/Asp (arranged in a different manner from that of the thiol proteases), seen in the other arginine-modifying enzymes is also conserved in ADI, as well as many other residues involved in substrate binding. Based on this conservation pattern and the assumption that the substrate binding mode is similar to that of DDAH, an ADI catalytic mechanism is proposed. The main players are Cys-406, which mounts the nucleophilic attack on the carbon atom of the guanidinium group of arginine, and His-278, which serves as a general base. (+info)
The evolution of parasite recognition genes in the innate immune system: purifying selection on Drosophila melanogaster peptidoglycan recognition proteins.
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Genes involved in the recognition of parasites by the acquired immune system are often subject to intense selection pressures. In some cases, selection to recognize a diverse range of parasites has resulted in high levels of polymorphism, while elsewhere the protein sequence has changed rapidly under directional selection. We tested whether parasite recognition genes in the innate immune system show similar patterns of evolution. We sequenced seven peptidoglycan recognition protein genes (PGRPs) from 12 lines of Drosophila melanogaster and one line of D. simulans and used a variety of tests to determine whether the observed mutations were selectively neutral. We were unable to detect either balancing or directional selection. This suggests that the molecular cues used by insects to detect parasites are highly conserved and probably under strong functional constraints which prevent their evolving to evade the host immune response. Therefore, interactions between these genes are unlikely to be the focus of host-parasite coevolution, at least in Drosophila. We also found evidence of gene conversion occurring between two genes, PGRP-SC1A and PGRP-SC1B. (+info)
Phylogenomics of the reproductive parasite Wolbachia pipientis wMel: a streamlined genome overrun by mobile genetic elements.
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The complete sequence of the 1,267,782 bp genome of Wolbachia pipientis wMel, an obligate intracellular bacteria of Drosophila melanogaster, has been determined. Wolbachia, which are found in a variety of invertebrate species, are of great interest due to their diverse interactions with different hosts, which range from many forms of reproductive parasitism to mutualistic symbioses. Analysis of the wMel genome, in particular phylogenomic comparisons with other intracellular bacteria, has revealed many insights into the biology and evolution of wMel and Wolbachia in general. For example, the wMel genome is unique among sequenced obligate intracellular species in both being highly streamlined and containing very high levels of repetitive DNA and mobile DNA elements. This observation, coupled with multiple evolutionary reconstructions, suggests that natural selection is somewhat inefficient in wMel, most likely owing to the occurrence of repeated population bottlenecks. Genome analysis predicts many metabolic differences with the closely related Rickettsia species, including the presence of intact glycolysis and purine synthesis, which may compensate for an inability to obtain ATP directly from its host, as Rickettsia can. Other discoveries include the apparent inability of wMel to synthesize lipopolysaccharide and the presence of the most genes encoding proteins with ankyrin repeat domains of any prokaryotic genome yet sequenced. Despite the ability of wMel to infect the germline of its host, we find no evidence for either recent lateral gene transfer between wMel and D. melanogaster or older transfers between Wolbachia and any host. Evolutionary analysis further supports the hypothesis that mitochondria share a common ancestor with the alpha-Proteobacteria, but shows little support for the grouping of mitochondria with species in the order Rickettsiales. With the availability of the complete genomes of both species and excellent genetic tools for the host, the wMel-D. melanogaster symbiosis is now an ideal system for studying the biology and evolution of Wolbachia infections. (+info)