Role of complex II in anaerobic respiration of the parasite mitochondria from Ascaris suum and Plasmodium falciparum.

Parasites have developed a variety of physiological functions necessary for existence within the specialized environment of the host. Regarding energy metabolism, which is an essential factor for survival, parasites adapt to low oxygen tension in host mammals using metabolic systems that are very different from that of the host. The majority of parasites do not use the oxygen available within the host, but employ systems other than oxidative phosphorylation for ATP synthesis. In addition, all parasites have a life cycle. In many cases, the parasite employs aerobic metabolism during their free-living stage outside the host. In such systems, parasite mitochondria play diverse roles. In particular, marked changes in the morphology and components of the mitochondria during the life cycle are very interesting elements of biological processes such as developmental control and environmental adaptation. Recent research has shown that the mitochondrial complex II plays an important role in the anaerobic energy metabolism of parasites inhabiting hosts, by acting as quinol-fumarate reductase.     

Triplet state of 4-methoxybenzyl alcohol chemisorbed on silica nanoparticles

The knowledge of photochemical kinetics in colloidal systems is important in understanding environmental photochemistry on dispersed solid surfaces. As model materials for the chemically sorbed organic compounds present in natural environments, modified silica nanoparticles (NPs) were obtained here by condensation of the silanol groups of fumed silica nanoparticles with 4-methoxybenzyl alcohol. These particles were characterized by different techniques. To evaluate their toxicity, the inhibition of the natural luminescence emission of the marine bacterium Vibrio fischeri in suspensions of the particles was measured. Laser flash-photolysis experiments (λ(exc) = 266 nm) performed with NP suspensions in acetonitrile-aqueous phosphate buffer mixtures showed the formation of the lowest triplet excited state of the chemisorbed organic groups (λ(max) = 390 nm). DFT calculations of the absorption spectrum of this radical support the assignment. From the calculated triplet energy, a thermodynamically favorable energy transfer from these triplet states to oxygen to yield singlet molecular oxygen is predicted. A value of 0.09 was measured for the quantum yield of singlet molecular oxygen generation by air-saturated suspensions of the nanoparticles in the mixture of solvents acetonitrile-aqueous phosphate buffer. The quantum yield of singlet molecular oxygen generation by the free 4-methoxybenzyl alcohol in the same solvent is 0.31.     

Energy generation in parasitic helminths

Although parasitic helminths are a very heterogeneous group of organisms, they share many interesting properties in their energy metabolism. In certain stages of their life cycle, they all have a large capacity for anaerobic functioning. In other stages, an aerobic energy metabolism prevails. Parasites have to adapt to different environments in which the availability of oxygen and food varies widely. These variations in their external conditions strongly influence their energy metabolism. Here, Louis Tielens presents an introduction to the current ideas on the bioenergetics of parasitic helminths, focusing on the differences in energy metabolism between various stages (free-living and parasitic), and paying special attention to the mechanisms involved in the transitions between the different methods of energy generation.     

Physiological uncoupling of mitochondrial oxidative phosphorylation. Studies in different yeast species

Under non-phosphorylating conditions a high proton transmembrane gradient inhibits the rate of oxygen consumption mediated by the mitochondrial respiratory chain (state IV). Slow electron transit leads to production of reactive oxygen species (ROS) capable of participating in deleterious side reactions. In order to avoid overproducing ROS, mitochondria maintain a high rate of O₂ consumption by activating different exquisitely controlled uncoupling pathways. Different yeast species possess one or more uncoupling systems that work through one of two possible mechanisms: i) Proton sinks and ii) Non-pumping redox enzymes. Proton sinks are exemplified by mitochondrial unspecific channels (MUC) and by uncoupling proteins (UCP). Saccharomyces. cerevisiae and Debaryomyces hansenii express highly regulated MUCs. Also, a UCP was described in Yarrowia lipolytica which promotes uncoupled O₂ consumption. Non-pumping alternative oxido-reductases may substitute for a pump, as in S. cerevisiae or may coexist with a complete set of pumps as in the branched respiratory chains from Y. lipolytica or D. hansenii. In addition, pumps may suffer intrinsic uncoupling (slipping). Promising models for study are unicellular parasites which can turn off their aerobic metabolism completely. The variety of energy dissipating systems in eukaryote species is probably designed to control ROS production in the different environments where each species lives.     

A trade-off between energy intake and exposure to parasites in oystercatchers feeding on a bivalve mollusc.

Models of animal dispersion between habitat patches that differ in resource density assume that animals maximize their fitness by maximizing the rate at which they consume resources. How valid is this assumption? Studies on wading birds have been central to the application of dispersion models to predator-prey systems. However, these birds do not always attempt to maximize their rate of energy intake, implying that maximization involves costs as well as benefits. Overwintering oystercatchers feeding on cockles in the Burry Inlet, South Wales, do not consume the larger more energetically profitable cockles even though consuming these prey would increase their rate of energy intake. This paper tests the hypothesis that maximizing energy intake involves a trade-off with exposure to helminth parasites. Cockles are important intermediate hosts for helminth parasites, for which oystercatchers are the definitive host. The helminth intensity of cockles increased significantly with cockle size. A functional response model was used to examine how size selection by the birds influenced energy intake and the ingestion rate of parasites. To maximize energy intake birds should selectively consume the larger size classes, but to minimize the ingestion rate of parasites they should consume the smallest size classes. In the wild, birds selectively consumed intermediate size classes, which could represent a compromise between these conflicting demands. The implications for animal dispersion models are discussed.     

Genomic insights into microbial iron oxidation and iron uptake strategies in extremely acidic environments

This minireview presents recent advances in our understanding of iron oxidation and homeostasis in acidophilic Bacteria and Archaea. These processes influence the flux of metals and nutrients in pristine and man-made acidic environments such as acid mine drainage and industrial bioleaching operations. Acidophiles are also being studied to understand life in extreme conditions and their role in the generation of biomarkers used in the search for evidence of existing or past extra-terrestrial life. Iron oxidation in acidophiles is best understood in the model organism Acidithiobacillus ferrooxidans. However, recent functional genomic analysis of acidophiles is leading to a deeper appreciation of the diversity of acidophilic iron-oxidizing pathways. Although it is too early to paint a detailed picture of the role played by lateral gene transfer in the evolution of iron oxidation, emerging evidence tends to support the view that iron oxidation arose independently more than once in evolution. Acidic environments are generally rich in soluble iron and extreme acidophiles (e.g. the Leptospirillum genus) have considerably fewer iron uptake systems compared with neutrophiles. However, some acidophiles have been shown to grow as high as pH 6 and, in the case of the Acidithiobacillus genus, to have multiple iron uptake systems. This could be an adaption allowing them to respond to different iron concentrations via the use of a multiplicity of different siderophores. Both Leptospirillum spp. and Acidithiobacillus spp. are predicted to synthesize the acid stable citrate siderophore for Fe(III) uptake. In addition, both groups have predicted receptors for siderophores produced by other microorganisms, suggesting that competition for iron occurs influencing the ecophysiology of acidic environments. Little is known about the genetic regulation of iron oxidation and iron uptake in acidophiles, especially how the use of iron as an energy source is balanced with its need to take up iron for metabolism. It is anticipated that integrated and complex regulatory networks sensing different environmental signals, such as the energy source and/or the redox state of the cell as well as the oxygen availability, are involved.     

A meta-analysis of factors affecting local adaptation between interacting species

Adaptive divergence among populations can result in local adaptation, whereby genotypes in native environments exhibit greater fitness than genotypes in novel environments. A body of theory has developed that predicts how different species traits, such as rates of gene flow and generation times, influence local adaptation in coevolutionary species interactions. We used a meta-analysis of local-adaptation studies across a broad range of host-parasite interactions to evaluate predictions about the effect of species traits on local adaptation. We also evaluated how experimental design influences the outcome of local adaptation experiments. In reciprocally designed experiments, the relative gene flow rate of hosts versus parasites was the strongest predictor of local adaptation, with significant parasite local adaptation only in the studies in which parasites had greater gene flow rates than their hosts. When nonreciprocal studies were included in analyses, species traits did not explain significant variation in local adaptation, although the overall level of local adaptation observed was lower in the nonreciprocal than in the reciprocal studies. This formal meta-analysis across a diversity of host-parasite systems lends insight into the role of both biology (species traits) and biologists (experimental design) in detecting local adaptation in coevolving species interactions.     

The flexibility of Apicomplexa parasites in lipid metabolism

Apicomplexa are obligate intracellular parasites responsible for major human infectious diseases such as toxoplasmosis and malaria, which pose social and economic burdens around the world. To survive and propagate, these parasites need to acquire a significant number of essential biomolecules from their hosts. Among these biomolecules, lipids are a key metabolite required for parasite membrane biogenesis, signaling events, and energy storage. Parasites can either scavenge lipids from their host or synthesize them de novo in a relict plastid, the apicoplast. During their complex life cycle (sexual/asexual/dormant), Apicomplexa infect a large variety of cells and their metabolic flexibility allows them to adapt to different host environments such as low/high fat content or low/high sugar levels. In this review, we discuss the role of lipids in Apicomplexa parasites and summarize recent findings on the metabolic mechanisms in host nutrient adaptation.     

Parasites grow larger in faster growing fish hosts

Parasites depend on host-derived energy for growth and development, and so are potentially affected by the host's ability to acquire nutrients under competitive foraging scenarios. Although parasites might be expected to grow faster in hosts that are better at acquiring nutrients from natural ecosystems, it is also possible that the most competitive hosts are better at countering infections, if they have an improved immune response or are able to limit the availability of nutrients to parasites. I first quantified the ability of uninfected three-spined sticklebacks Gasterosteus aculeatus to compete in groups for sequentially-presented food items, and then exposed either the best or worst competitors to infective stages of the cestode Schistocephalus solidus. Fish were subsequently raised in their original groups, under competitive feeding regimes, for 96 days, after which fish and parasite growth was determined. Unexpectedly, pre-exposure host competitive ability had no effect on susceptibility to infection, or on post-infection growth rate. Furthermore, despite a 120-fold variation in parasite mass at the end of the study, pre-infection competitive ability was not related to parasite growth. The closest predictor of parasite mass was body size-corrected host growth rate, indicating that the fastest growing fish developed the largest parasites. Faster growing hosts therefore apparently provide ideal environments for growing parasites. This finding has important implications for ecology and aquaculture.     

Protein targeting in parasites with cryptic mitochondria

Many highly specialised parasites have adapted to their environments by simplifying different aspects of their morphology or biochemistry. One interesting case is the mitochondrion, which has been subject to strong reductive evolution in parallel in several different parasitic groups. In extreme cases, mitochondria have degenerated so much in physical size and functional complexity that they were not immediately recognised as mitochondria, and are now referred to as 'cryptic'. Cryptic mitochondrion-derived organelles can be classified as either hydrogenosomes or mitosomes. In nearly all cases they lack a genome and all organellar proteins are nucleus-encoded and expressed in the cytosol. The same is true for the majority of proteins in canonical mitochondria, where the proteins are directed to the organelle by specific targeting sequences (transit peptides) that are recognised by translocases in the mitochondrial membrane. In this review, we compare targeting sequences of different parasitic systems with highly reduced mitochondria and give an overview of how the import machinery has been modified in hydrogenosomes and mitosomes.     

Boosting mediated electron transfer in bioelectrochemical systems with tailored defined microbial cocultures

Bioelectrochemical systems (BES) hold great promise for sustainable energy generation via a microbial catalyst from organic matter, for example, from wastewater. To improve current generation in BES, understanding the underlying microbiology of the electrode community is essential. Electron mediator producing microorganism like Pseudomonas aeruginosa play an essential role in efficient electricity generation in BES. These microbes enable even nonelectroactive microorganism like Enterobacter aerogenes to contribute to current production. Together they form a synergistic coculture, where both contribute to community welfare. To use microbial co‐operation in BES, the physical and chemical environments provided in the natural habitats of the coculture play a crucial role. Here, we show that synergistic effects in defined cocultures of P. aeruginosa and E. aerogenes can be strongly enhanced toward high current production by adapting process parameters, like pH, temperature, oxygen demand, and substrate requirements. Especially, oxygen was identified as a major factor influencing coculture behavior and optimization of its supply could enhance electric current production over 400%. Furthermore, operating the coculture in fed‐batch mode enabled us to obtain very high current densities and to harvest electrical energy for 1 month. In this optimized condition, the coulombic efficiency of the process was boosted to 20%, which is outstanding for mediator‐based electron transfer. This study lays the foundation for a rationally designed utilization of cocultures in BES for bioenergy generation from specific wastewaters or for bioprocess sensing and for benefiting from their synergistic effects under controlled bioprocess condition.     

Vampires,Pasteur and reactive oxygen species. Is the switch from aerobic to anaerobic metabolism a preventive antioxidant defence in blood-feeding parasites?

Several species of parasites show a reduction of their respiratory activity along their developmental cycles after they start to feed on vertebrate blood, relying on anaerobic degradation of carbohydrates to achieve their energy requirements. Usually, these parasites choose not to breathe despite of living in an environment of high oxygen availability such as vertebrate blood. Absence of the 'Pasteur effect' in most of these parasites has been well documented. Interestingly, together with the switch from aerobic to anaerobic metabolism in these parasites, there is clear evidence pointing to an increase in their antioxidant defences. As the respiratory chain in mitochondria is a major site of production of reactive oxygen species (ROS), we propose here that the arrest of respiration constitutes an adaptation to avoid the toxic effects of ROS. This situation would be especially critical for blood-feeding parasites because ROS produced in mitochondria would interact with pro-oxidant products of blood digestion, such as haem and/or iron, and increase the oxidative damage to the parasite's cells.     

BIOCHEMICAL ADAPTATION AND LOSS OF GENETIC CAPACITY IN HELMINTH PARASITES

1. Adaptation and loss of genetic capacity differ chiefly in that adaptation is goal- directed whereas loss of genetic capacity is not. Given sufficient information about an individual organism and its environment, adaptations are recognizable without reference to historical events extending beyond a single generation. This is not true of loss of genetic capacity, which requires a preliminary judgement that genetic information now absent was present in ancestral organisms. Together, adaptation and loss of genetic capacity are the major contributors to overall reproductive fitness. Accidental selection is genetically associated with adaptation, but is not goal-directed. 2. Adaptations arevariant or invariant; invariant adaptations comprising biochemical unity, and variant adaptations contributing to biochemical diversity. Variant adaptations may be either exploitive or epigenetic. Exploitive adaptations are a measure of thegenetic capacity for phenotypic response to an altered environment, which the individual may not in fact encounter. Epigenetic adaptations are more rigidly programmed and are responsive to altered environments only insofar as these are a constant feature of the life cycle. 3. Selected observations in the biochemistry of helminth parasites are examined with respect to their interpretation in terms of adaptation, loss of genetic capacity and accidental selection. Secure judgements concerning adaptation are often possible at the most general level, i.e. when the physicochemical properties of the environment, such as temperature or oxygen supply, are clearly defined. I t is more difficult to make judgements concerning the specific mechanisms used in achieving these goals. Conclusions concerning loss of genetic capacity require knowledge of the specific function through-out the life cycle. In many cases loss of genetic capacity is only apparent, as the function appears in another part of the life cycle. Such apparent losses are in reality epigenetic adaptations. These concepts are helpful in interpreting past work and in devising new experiments. 4. Development in helminth parasites includes a pronounced capacity for the orderly release of information to be used in the next stage. As each stage may require a radically different environment, programming for it may lead to phenomena which are superficially puzzling, such as the existence of aerobic electron transport systems in a stage whose energy metabolism is fermentative. The concept of epigenetic adaptation is especially useful for interpreting such observations. 5. Although possible adaptations are most readily apparent in biochemically complex mechanisms, these mechanisms are an expression of the orderly effects of many different primary gene products which have not been much studied. There are indications that organisms possessing relatively complex life cycles may provide opportunities for relating primary gene products, such as isozymes, to their physiological functions.     

Fish introduction and parasites in marine ecosystems: a need for information

Invasive species provide unique and useful systems by which to examine various ecological and evolutionary issues, both in terms of the effects on native environments and the subsequent evolutionary impacts. While biological invasions are an increasing agent of change in aquatic systems, alien species also act as vectors for new parasites and diseases. To date, colonizations by hosts and parasites have not been treated and reviewed together, although both are usually interwoven in various ways and may have unpredictable negative consequences. Fish are widely introduced worldwide and are convenient organisms to study parasites and diseases. We report a global overview of fish invasions with associated parasitological data. Data available on marine and freshwater are in sharp contrast. While parasites and diseases of inland freshwater fish, ornamental, reared and anadromous fish species are well documented, leading to the emergence of several evolutionary hypotheses in freshwater ecosystems during the last decade, the transfer of such organisms are virtually unexplored in marine ecosystems. The paucity of information available on the parasites of introduced marine fish reflects the paucity of information currently available on parasites of non-indigenous species in marine ecosystems. However, such information is crucial as it can allow estimations of the extent to which freshwater epidemiology/evolution can be directly transferred to marine systems, providing guidelines for adapting freshwater control to the marine environment.     

Hypoxic and nitrosative stress conditions modulate expression of myoglobin genes in a carcinogenic hepatobiliary trematode,Clonorchis sinensis

Despite recent evidence suggesting that adult trematodes require oxygen for the generation of bioenergy and eggshells, information on the molecular mechanism by which the parasites acquire oxygen remains largely elusive. In this study, the structural and expressional features of globin genes identified in Clonorchis sinensis, a carcinogenic trematode parasite that invades the hypoxic biliary tracts of mammalian hosts, were investigated to gain insight into the molecules that enable oxygen metabolism. The number of globin paralogs substantially differed among parasitic platyhelminths, ranging from one to five genes, and the C. sinensis genome encoded at least five globin genes. The expression of these Clonorchis genes, named CsMb (CsMb1—CsMb3), CsNgb, and CsGbX, according to their preferential similarity patterns toward respective globin subfamilies, exponentially increased in the worms coinciding with their sexual maturation, after being downregulated in early juveniles compared to those in metacercariae. The CsMb1 protein was detected throughout the parenchymal region of adult worms as well as in excretory-secretory products, whereas the other proteins were localized exclusively in the sexual organs and intrauterine eggs. Stimuli generated by exogenous oxygen, nitric oxide (NO), and nitrite as well as co-incubation with human cholangiocytes variously affected globin gene expression in live C. sinensis adults. Together with the specific histological distributions, these hypoxia-induced patterns may suggest that oxygen molecules transported by CsMb1 from host environments are provided to cells in the parenchyma and intrauterine eggs/sex organs of the worms for energy metabolism and/or, more importantly, eggshell formation by CsMb1 and CsMb3, respectively. Other globin homologs are likely to perform non-respiratory functions. Based on the responsive expression profile against nitrosative stress, an oxygenated form of secreted CsMb1 is suggested to play a pivotal role in parasite survival by scavenging NO generated by host immune cells via its NO dioxygenase activity.     

Healing while parasitized: impact of a naturally-occurring nematode during energy-intensive wound-healing in a beetle

The rigours of the daily lives of insects sometimes lead to minor injuries and wounds, which must be healed to avoid entry of pathogens and to resume normal function. Such healing requires energy, which must be diverted from other bodily reserves. What happens if energy reserves are already low, as would occur in individuals coping with internal parasites? This question is addressed in the presemt study, using horned passalus beetles (Odontotaenius disjunctus) and their naturally-occurring nematode Chondronema passali. Oxygen consumption rates are tested at rest, as well as after an experimental wound is applied, to evaluate energy requirements of wound-healing in parasitized and nonparasitized hosts. Furthermore, wound-healing rates are visually tracked with a numerical scoring system to directly measure the cost of parasitism on healing. At rest, parasitized beetles show no elevation in respiration (oxygen consumption). After wounding, the oxygen consumption of parasitized beetles is 10% higher than that in nonparasitized beetles. Beetles with moderate- to heavy worm burdens have slower healing than those with few or no nematodes. These results show that this parasite carries little cost to the host during day-to-day activities, whereas, during times of immediate energy demand, there is a cost; hosts require more energy to repair wounds, and the wounds take longer to close. This conclusion leads to the question of whether this parasite is truly benign, and how many other apparently benign parasites, in insects or other animals, have similar ‘hidden’ effects.     

The molecular diversity of freshwater picoeukaryotes reveals high occurrence of putative parasitoids in the plankton

Eukaryotic microorganisms have been undersampled in biodiversity studies in freshwater environments. We present an original 18S rDNA survey of freshwater picoeukaryotes sampled during spring/summer 2005, complementing an earlier study conducted in autumn 2004 in Lake Pavin (France). These studies were designed to detect the small unidentified heterotrophic flagellates (HF, 0.6-5 microm) which are considered the main bacterivores in aquatic systems. Alveolates, Fungi and Stramenopiles represented 65% of the total diversity and differed from the dominant groups known from microscopic studies. Fungi and Telonemia taxa were restricted to the oxic zone which displayed two fold more operational taxonomic units (OTUs) than the oxycline. Temporal forcing also appeared as a driving force in the diversification within targeted organisms. Several sequences were not similar to those in databases and were considered as new or unsampled taxa, some of which may be typical of freshwater environments. Two taxa known from marine systems, the genera Telonema and Amoebophrya, were retrieved for the first time in our freshwater study. The analysis of potential trophic strategies displayed among the targeted HF highlighted the dominance of parasites and saprotrophs, and provided indications that these organisms have probably been wrongfully regarded as bacterivores in previous studies. A theoretical exercise based on a new 'parasite/saprotroph-dominated HF hypothesis' demonstrates that the inclusion of parasites and saprotrophs may increase the functional role of the microbial loop as a link for carbon flows in pelagic ecosystems. New interesting perspectives in aquatic microbial ecology are thus opened.