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PubMed2006

Amino acid cost and codon-usage biases in 6 prokaryotic genomes: a whole-genome analysis.

For most prokaryotic organisms, amino acid biosynthesis represents a significant portion of their overall energy budget. The difference in the cost of synthesis between amino acids can be striking, differing by as much as 7-fold. Two prokaryotic organisms, Escherichia coli and Bacillus subtilis, have been shown to preferentially utilize less costly amino acids in highly expressed genes, indicating that parsimony in amino acid selection may confer a selective advantage for prokaryotes. This study confirms those findings and extends them to 4 additional prokaryotic organisms: Chlamydia trachomatis, Chlamydophila pneumoniae AR39, Synechocystis sp. PCC 6803, and Thermus thermophilus HB27. Adherence to codon-usage biases for each of these 6 organisms is inversely correlated with a coding region's average amino acid biosynthetic cost in a fashion that is independent of chemoheterotrophic, photoautotrophic, or thermophilic lifestyle. The obligate parasites C. trachomatis and C. pneumoniae AR39 are incapable of synthesizing many of the 20 common amino acids. Removing auxotrophic amino acids from consideration in these organisms does not alter the overall trend of preferential use of energetically inexpensive amino acids in highly expressed genes.

Adaptation, Biological↗

PubMed2003

The Leopoldina international symposium on parasitism, commensalism and symbiosis--common themes, different outcome.

The development of new methods, including genomics, which can even be applied to unculturable microorganisms, has significantly increased our knowledge about bacterial pathogenesis and symbiosis and, in consequence, is profoundly modifying our views on the evolution and the genetic and physiological basis of bacteria-host interactions. The presentations at this symposium revealed conceptual links between bacterial pathogenesis and symbiosis. The close co-operation of experts in both fields will result in significant synergy and new insights into basic mechanisms of bacteria-host interactions and their evolution. The meeting provided fascinating news about the genetic and metabolic consequences that the change in their lifestyle had for bacteria that developed from free-living to permanent host-associated organisms exemplified by intracellular pathogens or symbionts. In addition, surprising similarities but also striking differences between the strategies involved in the establishment of a symbiotic versus a parasitic lifestyle can be noted. In the long run, the characterization of such differences might lead to lifestyle prediction or to an evaluation of the pathogenic potential of newly isolated bacteria via the definition of genetic and/or metabolic signatures characteristic for pathogenic or symbiotic organisms. Moreover, it is expected that these investigations will lead to new strategies for the treatment or prevention of bacterial infections, or the avoidance of pathogen transmission.

Animals↗

PubMed2005

The coevolutionary dynamics of obligate ant social parasite systems--between prudence and antagonism.

In this synthesis we apply coevolutionary models to the interactions between socially parasitic ants and their hosts. Obligate social parasite systems are ideal models for coevolution, because the close phylogenetic relationship between these parasites and their hosts results in similar evolutionary potentials, thus making mutual adaptations in a stepwise fashion especially likely to occur. The evolutionary dynamics of host-parasite interactions are influenced by a number of parameters, for example the parasite's transmission mode and rate, the genetic structure of host and parasite populations, the antagonists' migration rates, and the degree of mutual specialisation. For the three types of obligate ant social parasites, queen-tolerant and queen-intolerant inquilines and slavemakers, several of these parameters, and thus the evolutionary trajectory, are likely to differ. Because of the fundamental differences in lifestyle between these social parasite systems, coevolution should further select for different traits in the parasites and their hosts. Queen-tolerant inquilines are true parasites that exert a low selection pressure on their host, because of their rarity and the fact that they do not conduct slave raids to replenish their labour force. Due to their high degree of specialisation and the potential for vertical transmission, coevolutionary theory would predict interactions between these workerless parasites and their hosts to become even more benign over time. Queen-intolerant inquilines that kill the host queen during colony take-over are best described as parasitoids, and their reproductive success is limited by the existing worker force of the invaded host nest. These parasites should therefore evolve strategies to best exploit this fixed resource. Slavemaking ants, by contrast, act as parasites only during colony foundation, while their frequent slave raids follow a predator prey dynamic. They often exploit a number of host species at a given site, and theory predicts that their associations are best described in terms of a highly antagonistic coevolutionary arms race.

Animals↗

PubMed1998

Australian helminths in Australian rodents: an issue of biodiversity.

The Australian public as well as Australian funding bodies are generally unsympathetic to native murids, rats and mice, in spite of the fact that 36% have either become extinct or critically endangered since European settlement. The endemic Australian parasites of these rats and mice have been even less sympathetically regarded. Prior to 1958 very little work was carried out on the helminths of Australian rodents and little more is known today. Records are known from only 28% of the extant host species, comprising some 109 species of helminth identified at least to generic level. The rodents invaded Australia from the north, perhaps through New Guinea in at least two separate waves, 5-8 then about 1 million years ago. The parasites they brought with them have adapted and speciated and there has been some host switching between rodent groups and between rodents and the Australian marsupials. This is illustrated particularly in the Trichostrongyloidea. The origins of the rodents from Southeast Asia down the Indonesian island chain are reflected in the presence of the nematode genus Tikusnema in both Australia and Indonesia, and Cyclodontostomum purvisi across Southeast Asia and into New Guinea. Hydromys chrysogaster, the Australian water-rat, illustrates how the biogeographical influences of the host's distribution and lifestyle can affect its parasite fauna. Most of the research to date is merely indicative of where more data are needed. The links between Australian and New Guinean helminth fauna, as well as the links between rodent and marsupial hosts and their fauna, cannot be determined without further research.

Animals↗

PubMed1999

Exploiting the life cycle of Strongyloides ratii.

The nematode Strongyloides ratti has a remarkable life cycle, which has both a parasitic and a free-living phase. The free-living phase includes a choice between two developmental routes. Here, Mark Viney discusses recent advances in understanding the biology of this developmental switch and shows how the life cycle of this nematode can be used to explore the lifestyle transitions common to all parasitic nematodes, as well as to address other basic biological questions.

Animals↗

PubMed2003

The amitochondriate eukaryote Trichomonas vaginalis contains a divergent thioredoxin-linked peroxiredoxin antioxidant system.

Trichomonas is an amitochondriate parasitic protozoon specialized for an anaerobic lifestyle. Nevertheless, it is exposed to oxygen and is able to cope with the resultant oxidative stress. In the absence of glutathione, cysteine has been thought to be the major antioxidant. We now report that the parasite contains thioredoxin reductase, which functions together with thioredoxin and thioredoxin peroxidase to detoxify potentially damaging oxidants. Thioredoxin reductase and thioredoxin also reduce cystine and so may play a role in maintaining the cellular cysteine levels. The importance of the thioredoxin system as one of the major antioxidant defense mechanisms in Trichomonas was confirmed by showing that the parasite responds to environmental changes resulting in increased oxidative stress by up-regulating thioredoxin and thioredoxin peroxidases levels. Sequence data indicate that the thioredoxin reductase of Trichomonas differs fundamentally in structure from that of its human host and thus may represent a useful drug target. The protein is generally similar to thioredoxin reductases present in other lower eukaryotes, all of which probably originated through horizontal gene transfer from a prokaryote. The phylogenetic signal in thioredoxin peroxidase is weak, but evidence from trees suggests that this gene has been subject to repeated horizontal gene transfers from different prokaryotes to different eukaryotes. The data are thus consistent with the complexity hypothesis that predicts that the evolution of simple pathways such as the thioredoxin cascade are likely to be affected by horizontal gene transfer between species.

Amino Acid Sequence↗

PubMed2000

Microsporidia and Cyclospora: epidemiology and assessment of risk from the environment.

Two classes of parasites with an environmental stage in their lifestyle have recently emerged as significant gastrointestinal pathogens for humans. Microsporidia represent a group that contains a number of genera related to the genus Cryptosporidium. They are generally transmitted via direct human to human contact, but can survive in water and food, and recently have been found in surface water used as drinking source water. Their most common host range is in patients with clinical AIDS. Limited work to date suggests the group is susceptible to chlorine achievable CxT (concentration x time) values and is coagulated by filtration. Cyclospora cayetanensis is a species of parasite that has caused outbreaks from contaminated food. Its major risk is from the use of inadequately treated water used for irrigation. Cyclospora can infect normal and immunosuppressed hosts. Current information regarding the lifestyle, transmission, and control of both groups of parasites are discussed, with a health risk assessment analysis.

Animals↗

PubMed2002

Is Toxoplasma egress the first step in invasion?

The protozoan parasite Toxoplasma gondii maintains an intracellular lifestyle that requires careful timing and coordination when exiting one cell (egress) and entering another (invasion). Here it is argued that T. gondii uses similar molecular mechanisms for egress and invasion, based on common morphology, dependence on motility, and regulation by a calcium-dependent signal transduction pathway. In our view, this strategy is highly advantageous because it allows the parasite to egress rapidly from one cell and immediately invade an adjacent cell, thereby minimizing exposure to the extracellular environment where it could be destroyed by host immune mediators.

Animals↗

PubMed1995

The varied lifestyles of intracellular pathogens within eukaryotic vacuolar compartments.

Many bacterial pathogens and eukaryotic parasites can enter mammalian cells and live intracellularly inside membrane-bound vacuoles. The intravacuolar lifestyle of these pathogens plays a key role in pathogenesis. Understanding the molecular basis of the development of these specialized intracellular compartments is critical to understanding how these organisms cause disease.

Animals↗

PubMed2001

Invasion and persistent intracellular colonization of erythrocytes. A unique parasitic strategy of the emerging pathogen Bartonella.

The expanding genus Bartonella includes zoonotic and human-specific pathogens that can cause a wide range of clinical manifestations. A productive infection allowing bacterial transmission by blood-sucking arthropods is marked by an intraerythrocytic bacteremia that occurs exclusively in specific human or animal reservoir hosts. Incidental human infection by animal-adapted bartonellae can cause disease without evidence for erythrocyte parasitism. A better understanding of the intraerythrocytic lifestyle of bartonellae may permit the design of strategies to control the reservoir and transmittable stages of these emerging pathogens. We have dissected the process of Bartonella erythrocyte parasitism in experimentally infected animals using a novel approach for tracking blood infections based on flow cytometric quantification of green fluorescent protein-expressing bacteria during their interaction with in vivo-biotinylated erythrocytes. Bacteremia onset occurs several days after inoculation by a synchronous wave of bacterial invasion into mature erythrocytes. Intracellular bacteria replicate until reaching a stagnant number, which is sustained for the remaining life span of the infected erythrocyte. The initial wave of erythrocyte infection is followed by reinfection waves occurring at intervals of several days. Our findings unravel a unique bacterial persistence strategy adapted to a nonhemolytic intracellular colonization of erythrocytes that preserves the pathogen for efficient transmission by blood-sucking arthropods.

Animals↗

PubMed2003

Phylogenetic insights into the evolution of parasitism in hymenoptera.

The Hymenoptera are one of the four megadiverse orders of insects, with over 100000 described species and several times this number still waiting to be described. A major part of this diverse group is formed of large lineages of parasitoid wasps. Some of these lineages have in turn given rise to subgroups that have gone on to diversify into other lifestyles, such as gall-forming on, and pollination of, plants, as well as a broad array of food-collecting behaviors associated with social living in colonies. Thus, the Hymenoptera demonstrate the large evolutionary potential of parasitism as a lifestyle, in contrast to early assertions that parasitism tends to lead to evolutionary 'dead ends' driven by overspecialization. Phylogenetic approaches have already led to a number of important insights into the evolution of parasitism in Hymenoptera. A series of examples are discussed in this review, including the origin of parasitism in the order, the development of koinobiosis in some groups, coevolution with symbiotic viruses, and the evolution in some groups away from parasitism and into such habits as gall formation, pollination of figs, nest building and sociality. The potential for comparative analysis of hymenopteran habits is large, but progress is still in its early stages due to the paucity of available well-supported phylogenies, and the still limited accumulation of basic biological data for many taxa.

Animals↗

PubMed2002

Diversity in the Monogenea and Digenea: does lifestyle matter?

If the cestodes are excluded, then the parasitic platyhelminths of fishes divide neatly into the external and monoxenous Monogenea and the internal and heteroxenous Digenea. Both groups have apparently had long associations of coevolution, host switching and adaptation with fishes and have become highly successful in their respective habitats. Current estimates of species richness for the two groups suggest that they may be remarkably similar. Here we consider the nature of the diversity of the Monogenea and Digenea of fishes in terms of richness of species and higher taxa to determine what processes may be responsible for observed differences. The Monogenea includes at least two super-genera (Dactylogyrus and Gyrodactylus) each of which has hundreds of species; no comparable genera are found in the Digenea. Possible reasons for this difference include the higher host specificity of monogeneans and their shorter generation time. If allowance is made for the vagaries of taxonomic 'lumping' and 'splitting', then there are probably comparable numbers of families of monogeneans and digeneans in fishes. However, the nature of the families differ profoundly. Richness in higher taxa (families) in the Digenea is explicable in terms of processes that appear to have been unimportant in the Monogenea. Readily identifiable sources of diversity in the Digenea are: recolonisation of fishes by taxa that arose in association with tetrapods; adoption of new sites within hosts; adoption of new diets and feeding mechanisms; adaptations relating to the exploitation of ecologically similar groups of fishes and second intermediate hosts; and adaptations relating to the exploitation of phylogenetic lineages of molluscs. In contrast, most higher- level monogenean diversity (other than that associated with the subclasses) relates principally to morphological specialisation for attachment by the haptor.

Animals↗

PubMed2001

The structure of mast cell secretory granules in the blind mole rat (Spalax ehrenbergi).

Eosinophils, basophils, and mast cells produce and secrete active substances whose role is to attack invading parasites and protect the host. In this study we use morphometric methods to study mast cells in the blind mole rat (Spalax ehrenbergi). The subterranean and solitary way of life of this species has led to the evolutionary development of special anatomical, morphological, behavioral, and physiological adaptations. Because of its particular lifestyle, the mole rat is less exposed to parasites than other rodents. This could provide a unique model for research into the pathobiology of mast cells. The paracrystalline structure of the mast cell granule content is composed of parallel plates. Diffraction analysis of electron micrographs of thin sections of araldite-embedded tissues indicated that each crystal line plate is a periodic array of parallelograms. The crystal unit cell volume is approximately 930 nm(3), suggesting that each unit cell is composed of one heparin molecule and one to three additional adsorbed proteins. Morphometric data show that characteristics of the secretory granules of mast cells of the blind mole rat resemble those of other rodents. The mast cell unit granule volume in the present study was calculated to be 0.055 microm(3), similar to that of rat peritoneal mast cells.

Animals↗

PubMed1997

Adaptations in scale insects.

Many unusual features of scale insects (Hemiptera: Coccoidea) can be explained as historical legacy. Developmental specializations in ancestral coccoids resulted in a neotenous adult female and a drastic metamorphosis of the male. Subsequent evolution led to numerous, often convergently derived, adaptations to parasitic life on higher plants. The sedentary lifestyle of female scale insects has favored the evolution of appendage reduction or loss, gross changes in body shape, and protective wax secretions, tests, and other scale covers. Morphological peculiarities of adult males relate to flight or to mating with concealed females. Scale insects have diverse egg-protecting methods, a range of chromosome behaviors (including several methods of sex determination), marked sexual dimorphism [even sometimes in first-instar nymphs (crawlers)], and more rarely sexual dichronism. Crawlers have evolved as the main agents of dispersal. The biotic interactions of scale insects include diverse endosymbioses with microorganisms, sometimes morphological and behavioral adaptations for obligate association with ants, and often highly specific host-plant associations that may lead to demic adaptation or the evolution of complex galls.

Journal Article↗

PubMed2006

Bacterial populations as perfect gases: genomic integrity and diversification tensions in Helicobacter pylori.

Microorganisms that persist in single hosts face particular challenges. Helicobacter pylori, an obligate bacterial parasite of the human stomach, has evolved a lifestyle that features interstrain competition and intraspecies cooperation, both of which involve horizontal gene transfer. Microbial species must maintain genomic integrity, yet H. pylori has evolved a complex nonlinear system for diversification that exists in dynamic tension with the mechanisms for ensuring fidelity. Here, we review these tensions and propose that they create a dynamic pool of genetic variants that is sufficiently genetically diverse to allow H. pylori to occupy all of the potential niches in the stomach.

Biological Evolution↗

PubMed1994

Phylogenetic analysis of RNA editing: a primitive genetic phenomenon.

RNA editing by extensive uridine addition and deletion creates over 90% of the amino acid codons in the cytochrome-c oxidase subunit III (COIII) transcript in Trypanosoma brucei and Herpetomonas, whereas editing of the COIII transcripts in Leishmania tarentolae and Crithidia fasciculata generates only 6% of the amino acid codons and is limited to the 5' ends. Is extensive RNA editing a primitive or derived character? We constructed a phylogenetic tree based on nuclear small-subunit and mitochondrial large- and small-subunit ribosomal RNA sequences for nine species of kinetoplastid protozoa. Our results suggest that extensive editing is a primitive genetic phenomenon that has disappeared in recent evolutionary time and also that there have been multiple losses of the digenetic lifestyle by loss of the vertebrate host in parasite evolution.

Animals↗

PubMedDate not supplied

The haematology of indigenous Australians.

Prior to European settlement indigenous Australians were hunter-gatherers who lived in geographically isolated small clan groups, also separated by elaborate totemic rules. Today they still reside in isolated communities throughout Australia but many have moved to the cities. They share a high incidence of a range of health problems including cardiovascular disease, renal disease and infectious diseases largely attributed to a change to a more sedentary lifestyle. This paper reviews the haematology of indigenous Australians, including blood count, frequency and causes of anaemia, inherited risk factors for thrombophilia, blood groups and the incidence and types of haematological malignancies. There are some significant genetic differences between indigenous and non-indigenous Australians particularly in the frequency of blood groups, factor V Leiden and prothrombin mutations and presence of -alpha3.7 kb thalassaemia. These findings may have practical therapeutic implications (e.g. HPA phenotype for transfusion therapy and pregnancy risk) and in predicting disease risk. Other differences are acquired, related to lifestyle and living conditions (e.g. eosinophilia secondary to parasitic infections; iron and folate deficiencies), and are largely preventable.

Australia↗

PubMed1983

National case-control study of Kaposi's sarcoma and Pneumocystis carinii pneumonia in homosexual men: Part 2. Laboratory results.

The Centers for Disease Control conducted a case-control study to investigate an outbreak of Kaposi's sarcoma and Pneumocystis carinii pneumonia in homosexual men. The occurrence of these diseases was found to be associated with certain aspects of lifestyle, including a greater number of male sex partners per year, exposure to feces during sex, history of syphilis and non-B hepatitis, treatment for enteric parasites, and use of various illicit substances. Laboratory studies reflected both this lifestyle and the probable underlying cause of the Kaposi's sarcoma and P. carinii pneumonia--cellular immune deficiency. Patients were found to have lymphopenia, specifically a deficiency of the T-helper subpopulation, resulting in a reversal of the T-helper to T-suppressor ratio. Levels of IgG and IgA were increased. When compared with controls, patients were also found to have significantly higher titers of antibody to Epstein-Barr virus and cytomegalovirus, a higher prevalence of antibody to hepatitis A virus and Treponema pallidum, a lower prevalence of antibody to varicella zoster virus, and a higher frequency of isolation of cytomegalovirus.

Acquired Immunodeficiency Syndrome↗