Arthropod-transmitted Parasites: Mechanisms of Immune Interaction

Knowledge of arthropod immune mechanisms has been based to alarge extent on studies of non-medically important arthropod-microbialinteractions. Investigations involving arthropods and theirimmune responses against helminth and protozoan parasites theytransmit to vertebrate hosts are relatively limited. Data availablestrongly suggest that effective responses against these parasitesare hemocyte mediated reactions, with blood cells involved inparasite recognition and effector mechanisms. It also is apparentthat parasites are very successful in evading immune destructionin compatible arthropodparasite associations by avoiding immunedetection and/or by actively inhibiting the immune processes.However, an understanding of immune evasion mechanisms operatingon behalf of the parasite is dependent on a more thorough understandingof parasite recognition, signal transduction, and effector mechanismsinvolved in arthropod immunity. Limited data are available onhemocyte recognition events, and nothing is known about thetransduction processes whereby cells convert extracellular signalsto intracellular messages that activate effector mechanisms.Any significant progress in these important areas of researchwill be limited until successful in vitro hemocyte culturesare developed. Convincing data are available from a varietyof arthropod-parasite systems that phenol oxidases play a majorrole in effector mechanisms of the immune response. However,critical biochemical studies are needed to clarify their substratespecificities and the uniqueness of these enzymes. It is essentialthat we identify specific substrates involved in effector mechanisms,and their potential storage forms, if we are to begin to understandimmune processes in arthropods. The sensitivity of HPLC withelectrochemical detection provides a valuable tool for theseinvestigations. The next several years should prove excitingin regard to our understanding of molecular/biochemical processesof arthropod immunity.     

Mechanisms of Pathogenesis, Infective Dose and Virulence in Human Parasites

The number of pathogens that are required to infect a host, termed infective dose, varies dramatically across pathogen species. It has recently been predicted that infective dose will depend upon the mode of action of the molecules that pathogens use to facilitate their infection. Specifically, pathogens which use locally acting molecules will require a lower infective dose than pathogens that use distantly acting molecules. Furthermore, it has also been predicted that pathogens with distantly acting immune modulators may be more virulent because they have a large number of cells in the inoculums, which will cause more harm to host cells. We formally test these predictions for the first time using data on 43 different human pathogens from a range of taxonomic groups with diverse life-histories. We found that pathogens using local action do have lower infective doses, but are not less virulent than those using distant action. Instead, we found that virulence was negatively correlated with infective dose, and higher in pathogens infecting wounded skin, compared with those ingested or inhaled. More generally, our results show that broad-scale comparative analyses can explain variation in parasite traits such as infective dose and virulence, whilst highlighting the importance of mechanistic details.     

3类水生植物对池塘养殖废水氮磷去除效果的研究

在人工模拟条件下,利用室内试验桶培育,研究了挺水植物芦苇、沉水植物金鱼藻和浮叶植物浮叶四角菱对池塘养殖废水的净化效果.结果表明,3类植物都能有效吸收废水中过剩的氮磷营养物质,经过50 d植物处理,它们对水体中氮素去除率表现为芦苇(80.8%)>浮叶四角菱(62.6% )>金鱼藻(34.4%),对磷素去除率表现为芦苇(73.2%)>金鱼藻(27.1%)>浮叶四角菱(17.2%);芦苇和金鱼藻对池塘养殖废水环境适应性较强,植物平均存活率分别可达85%和60%,而浮叶四角菱的适应性较差,存活率基本维持在45%以下.可见,在相同条件下脱氮除磷效果最好的是挺水植物(芦苇),其次脱氮效果较好的是浮叶植物(浮叶四角菱),而除磷效果较好的则是沉水植物(金鱼藻).     

Mechanisms and Consequences of Developmental Acceleration in Tadpoles Responding to Pond Drying

Many amphibian species exploit temporary or even ephemeral aquatic habitats for reproduction by maximising larval growth under benign conditions but accelerating development to rapidly undergo metamorphosis when at risk of desiccation from pond drying. Here we determine mechanisms enabling developmental acceleration in response to decreased water levels in western spadefoot toad tadpoles (Pelobates cultripes), a species with long larval periods and large size at metamorphosis but with a high degree of developmental plasticity. We found that P. cultripes tadpoles can shorten their larval period by an average of 30% in response to reduced water levels. We show that such developmental acceleration was achieved via increased endogenous levels of corticosterone and thyroid hormone, which act synergistically to achieve metamorphosis, and also by increased expression of the thyroid hormone receptor TRΒ, which increases tissue sensitivity and responsivity to thyroid hormone. However, developmental acceleration had morphological and physiological consequences. In addition to resulting in smaller juveniles with proportionately shorter limbs, tadpoles exposed to decreased water levels incurred oxidative stress, indicated by increased activity of the antioxidant enzymes catalase, superoxide dismutase, and gluthatione peroxidase. Such increases were apparently sufficient to neutralise the oxidative damage caused by presumed increased metabolic activity. Thus, developmental acceleration allows spadefoot toad tadpoles to evade drying ponds, but it comes at the expense of reduced size at metamorphosis and increased oxidative stress.     

Removal of Styrene from Waste Gas Using a Biological Trickling Filter

Biodegradation of styrene in a biological trickling filter on lava stones was investigated, firstly, with the addition of silicon oil and, secondly, without the addition of silicon oil. After 400 days of trial runs the experimental results revealed that the biodegradation capacity of styrene in the trickling filter reached 537 g/m³ × h with a degradation yield of 96.8 % at an air inlet concentration of 1.06 g/m³ of styrene and a space velocity of 157 m/h in the presence of silicon oil. A removal of styrene up to 2.9 kg/m³ × h was obtained when the styrene input concentration in a constant inlet air flow of 0.78 m³/h was increased up to 6.6 g/m³. Interestingly, it was observed that after a period of 400 days, the seven dominant strains were completely different from those present in the inoculum. Surprisingly, this population was able to grow in an aqueous liquid phase without silicon oil on a styrene concentration of 45.5 g/L. In the biological trickling filter with lava stones but without silicon oil, the biodegradation capacity of styrene was 464 g/m³ × h with a removal yield of 98.3 % at an air inlet concentration of 1.03 g/m³ of styrene and a space velocity of 137 m/h. As in the presence of silicon oil, a removal of styrene of up to 2.375 kg/m³ × h was achieved when the air flow rate was kept constant and the styrene input concentration was increased. These experiments suggested that the biphasic medium could be very efficiently used for the selection of adapted strains for the removal of insoluble or poorly soluble organic compounds, rather than being used for long‐term degradation under industrial conditions.     

Composition of Microbial Fouling on the Surface of Plastics and Steel Exposed in a Pond at a Solid Waste Landfill

Microbiology - The work was aimed at investigation of the composition of microbial communities formed on the surface of samples of polyethylene terephthalate (PET), polystyrene (PS) and steel (ST)...     

A Passion for Parasites

I knew nothing and had thought nothing about parasites until 1971. In fact, if you had asked me before then, I might have commented that parasites were rather disgusting. I had been at the Johns Hopkins School of Medicine for three years, and I was on the lookout for a new project. In 1971, I came across a paper in the Journal of Molecular Biology by Larry Simpson, a classmate of mine in graduate school. Larry''s paper described a remarkable DNA structure known as kinetoplast DNA (kDNA), isolated from a parasite. kDNA, the mitochondrial genome of trypanosomatids, is a DNA network composed of several thousand interlocked DNA rings. Almost nothing was known about it. I was looking for a project on DNA replication, and I wanted it to be both challenging and important. I had no doubt that working with kDNA would be a challenge, as I would be exploring uncharted territory. I was also sure that the project would be important when I learned that parasites with kDNA threaten huge populations in underdeveloped tropical countries. Looking again at Larry''s paper, I found the electron micrographs of the kDNA networks to be rather beautiful. I decided to take a chance on kDNA. Little did I know then that I would devote the next forty years of my life to studying kDNA replication.     

Microbial Waste Biomass for Removal of Chromium(VI) from Chrome Effluent

ABSTRACT

Microbial waste biomass, a by-product of the fermentation industry, was developed as a biosorbent to remove hexavalent chromium (Cr) from the acidic effluent of a metal processing industry. In batch sorption, 100% Cr(VI) removal was achieved from aqueous solution in 30 min contact at pH 4.0–5.0. The Cr(VI) sorption equilibrium was evaluated using the Langmuir and Freundlich models, indicating the involvement of ion exchange and physicochemical interaction. Fourier transform infrared (FTIR) analysis revealed the presence of amine, hydroxyl, and imine functional groups present on the surface of microbial biomass that are involved in Cr binding. In a continuous sorption system, 95 mg L^?1 of Cr(VI) was adsorbed before the column reached a breakthrough point of 0.1 mg L^?1 Cr(VI) at the column outlet. An overall biosorption capacity of 12.6 mg Cr(VI) g^?1 of dry microbial waste was achieved, including the partially saturated portion of the dynamic sorption zone. Insignificant change in metal removal was observed up to 10 cycles. In pilot-scale studies, 100% removal of Cr(VI) was observed up to 5 weeks, and the method was found to be cost-effective, commercially viable, and environmentally friendly, as it does not generate toxic chrome sludge.     

Parasites from feral pigeons as a health hazard for humans

Feral pigeons live in almost every large city in the world. The feeding of pigeons by humans, deliberately or accidentally, allows the build‐up of large populations that can cause a variety of problems, primarily the fouling of buildings and monuments by their droppings. Excreta of wild birds are a well‐known source of pathogenic microorganisms that can cause infection in man. The most important ectoparasites of feral pigeons are the red blood mite, Dermanyssus gallinae, and the pigeon tick, Argas reflexus, both of which can migrate into human living space when they lose their natural hosts. The bites of the red blood mite are irritating but harmless, whereas the pigeon tick can cause severe health problems to predisposed persons. After repeated bites from A. reflexus, people can develop IgE‐mediated (type I) allergy, which in extreme situations may lead to life‐threatening symptoms of anaphylactic shock. So far, one fatality due to A. reflexus deriving from feral pigeons has been reported. In the case of parasitic infestations of humans, the source must be removed by excluding pigeons from further breeding and by disinfection of the environment of pigeon‐breeding sites.     

Parasites promote host gene flow in a metapopulation

Local adaptation is a powerful mechanism to maintain genetic diversity in subdivided populations. It counteracts the homogenizing effect of gene flow because immigrants have an inferior fitness in the new habitat. This picture may be reversed in host populations where parasites influence the success of immigrating hosts. Here we report two experiments testing whether parasite abundance and genetic background influences the success of host migration among pools in a Daphnia magna metapopulation. In 22 natural populations of D. magna, immigrant hosts were found to be on average more successful when the resident populations experienced high prevalences of a local microsporidian parasite. We then determined whether this success is due to parasitism per se, or the genetic background of the parasites. In a common garden competition experiment, we found that parasites reduced the fitness of their local hosts relatively more than the fitness of allopatric host genotypes. Our experiments are consistent with theoretical predictions based on coevolutionary host-parasite models in metapopulations. A direct consequence of the observed mechanism is an elevated effective migration rate for the host in the metapopulation.     

Parasites as probes for biodiversity.

Cestodes of the genus Linstowia, parasitic in marsupials, show patterns of coevolution and ancient historical-ecological connections. Correlated with the breakup of the austral landmasses (Gondwanaland) of the Neotropical and Australian regions from the Antarctic continent, the age of this host-parasite community is estimated to be between 60 and 70 million years old. Based on the data from the survey of parasites of mammals from throughout Bolivia and from the phylogenetic analysis of the cestodes, we urge the planners of biodiversity preserves in the neotropics to consider the Yungas of Bolivia as a region that supports an ancient ecological community worthy of consideration as a biopreserve.     

Pond canopy cover: a resource gradient for anuran larvae

1. The gradient in pond canopy cover strongly influences freshwater species distributions. This study tested the effects of canopy cover on the performance of two species of larval anurans, a canopy cover generalist (Rana sylvatica, the wood frog) and an open‐canopy specialist (R. pipiens, the leopard frog), and tested which factors co‐varying with canopy cover mediate these effects. 2. A field transplant experiment demonstrated that canopy cover had negative performance effects on both species. However, leopard frogs, which grow faster than wood frogs in open‐canopy ponds, were more strongly affected by closed‐canopy pond conditions. 3. Closed‐canopy ponds had lower temperature, dissolved oxygen (DO), and food nutritional quality as indicated by carbon‐to‐nitrogen ratio (C : N) analysis of field‐sampled food types, and of gut contents of transplanted larvae. 4. Laboratory experiments demonstrated that higher temperature and food quality but not DO substantially increased larval growth. However, only food quality increased growth rates of leopard frogs more than wood frogs. 5. The strong correlation of growth rates to gut content C : N in the field, and the similarity of growth curves as a function of resource quality in the field and laboratory, strongly suggest that resources are of primary importance in mediating intraspecific, and especially interspecific differences in performance across the canopy cover gradient.