Host-parasite relationships in gamasid mites of the genus Hirstionyssus (Acari:Parasitiformes:Gamasina) in the south of the West Siberian Plain

The paper reports data on host-parasite relationships in gamasid mites of the genus Hirstionyssus Fonseca and small mammals in the south of the West Siberian Plain.     

The reaction of near-isogenic lines of flax to the rust fungus Melampsora lini. II. Biochemical studies

The nature of resistance to rust fungus Melampsora lini (Pers.) Lev. was studied in two near-isogenic lines of flax, the susceptible Redwing (rr) and the immune S-66-53 (RR). Proteins of theses lines were immunologically and electrophoretically similar. Hydrolytic enzymes which release phenolic moities, i.e., -glucosidase and esterase(s), and phenol-oxidizing enzymes, i.e., peroxidase and polyphenol oxidase(s), did not appear to be involved in resistance or susceptibility as controlled by the R locus. Catalase activity was found to be higher in younger tissues of Redwing than in S-66-53 or their immune F₁ hybrid (Rr). Older tissues in both lines, whether inoculated or not, did not show any detectable catalase activity. A hypothesis to explain the genetic control of resistance and susceptibility in these lines before and after inoculation is suggested.This work has been supported by the National Research Council of Canada.     

The Ultrastructure of the Host-parasite Interface in the Needles of Pinus nigra Infected with Lophodermella sulcigena

The hyphae of Lophodermella sulcigena are usually surroundedby an electron-opaque matrix when growing in the needles ofCorsican pine (Pinus nigra var. maritima). The host-parasiteinterface is of a type which has been little studied; the intercellularhyphae kill the mesophyll cells of the host ahead of themselvesand their walls are separated from those of the host by a matrix.The first signs of injury to the host are disorganized membranesystems, particularly the thylakoid and bounding membranes ofthe chloroplasts break down. The dead host cells are filledwith resin or tannin in which only the starch grains are visible.     

Nutritional Immunity: S100 Proteins at the Host-Pathogen Interface

The S100 family of EF-hand calcium (Ca²⁺)-binding proteins is essential for a wide range of cellular functions. During infection, certain S100 proteins act as damage-associated molecular patterns (DAMPs) and interact with pattern recognition receptors to modulate inflammatory responses. In addition, these inflammatory S100 proteins have potent antimicrobial properties and are essential components of the immune response to invading pathogens. In this review, we focus on S100 proteins that exhibit antimicrobial properties through the process of metal limitation, termed nutritional immunity, and discuss several recent advances in our understanding of S100 protein-mediated metal sequestration at the site of infection.     

Hatching asynchrony, nestling competition, and the cost of interspecific brood parasitism

All parental hosts of heterospecific brood parasites must paythe cost of rearing non-kin. Previous research on nest parasitismby brown-headed cowbirds (Molothrus ater) concluded that competitivesuperiority of the typically more intensively begging and largercowbird chick leads to preferential feeding by foster parentsand causes a reduction in the hosts' own brood. The larger sizeof cowbird nestlings can be the result of at least two causes:(1) cowbirds preferentially parasitize species with smallernestlings and lower growth rates; and/or (2) cowbirds hatchearlier than hosts. I estimated the cost of cowbird parasitismfor each of 29 species by calculating the difference betweenhosts' published brood sizes in nonparasitized and parasitizednests and using clutch size to standardize values. In this analysis,greater incubation length and lower adult mass, surrogate measuresof the hatching asynchrony and size difference between parasiteand hosts, were both related to greater costs of cowbird parasitismwithout bias owing to phylogeny. To establish causality, I manipulatedclutch contents of eastern phoebes (Sayornis phoebe) and examinedwhether earlier hatching by a single cowbird or phoebe egg reducesthe size of the rest of the original host brood. As predicted,greater hatching asynchrony increased the proportion of theoriginal phoebe brood that was lost. This measure of the costof parasitism was partially owing to increased hatching failureof the original eggs in asynchronous broods but was not at allrelated to the size differences of older and younger conspecificnestmates. However, proportional brood loss owing to an earlierhatching conspecific was consistently smaller than brood lossowing to asynchronous cowbirds in both naturally and experimentallyparasitized phoebe nests. These results imply that althoughhatching asynchrony is an important cause of the reduction ofhost broods in parasitized clutches, competitive features ofcowbird nestlings remain necessary to explain the full extentof hosts' reproductive costs caused by interspecific brood parasitism.     

Protosporangium: a New Genus of Protostelids*

Protosporangium is described as a new genus of the mycetozoan order Protosteliida, with 3 new species: P. bisporum, P. fragile , and P. articulatum . The genus is characterized by minute, mostly 2-4-spored sporangia borne on long, slender, flexuous stalks. The spores produce flagellate cells (typically 8 per sporangium) during germination. The trophic stage is holozoic and uninucleate to plurinucleate but never reticulate. Plurinucleate protoplasts segment into uninucleate (sometimes binucleate) prespore cells that culminate to form sporocarps in the manner characteristic of protostelids.     

Characterization of a 24 kD parasitism-specific hemolymph protein from pharate pupae of the caribbean fruit fly,Anastrepha suspensa

A parasitism-specific protein was originally identified in the hemolymph of the Caribbean fruit fly Anastrepha suspensa parasitized by the braconid wasp Diachasmimorpha (Biosteres) longicaudata using single-dimensional (1-D) sodium dodecyl sulfate (SDS) PAGE. We now show that the protein is comprised of two closely migrating species both of which are glycoproteins of ≈? 24,000 Daltons (24 kD). The proteins were poorly resolved from whole hemolymph by 1-D SDS PAGE, but were well resolved by two-dimensional (2-D) PAGE and isoelectric focusing. They have pl's of ≈? 6.3 and 6.7 and contain Man residues, based on their affinity for concanavalin A (Con A). The presence of GlcNAc, NeuAc, and GalNAc residues in both proteins was implicated by their binding to wheat germ agglutinin (WGA). The proteins bound WGA more intensely following mannosidase treatment which eliminated their affinity to Con A and further implicated the presence of internal GlcNAc residues. However, binding of the proteins to WGA in the presence of competing GlcNAc (1 M) was reduced but not eliminated and suggested that in addition to GlcNAc, other WGA-binding sugar moieties, possibly NeuAc, a Sia, were present. To evaluate the presence of NeuAc, we treated the hemolymph with Vibrio cholerae neuraminidase which specifically cleaves terminal Sia. Samples of the neuraminidase-digested proteins were evaluated by WGA binding and Western blotting with the use of an anti-24 kD rabbit polyclonal serum to determine whether desialation eliminated the proteins' affinity to WGA or their immunoreactivity. Our results show that partial digestion of the 24 kD proteins with Vibrio cholerae neuraminidase resulted in two immunoreactive bands in Western blots of 1-D gels but only one of these, the upper undigested 24 kD band, bound WGA. This confirmed the presence of Sia residues in the proteins and demonstrated that desialation increased their relative electrophoretic mobilities. © 1994 Wiley-Liss, Inc.     

Basidiomycete cryopreservation on perlite: evaluation of a new method

A new cryopreservation method using perlite as a carrier was evaluated on a large set of mycelial cultures of basidiomycetes. The viability and some other characteristics--growth, macro- and micromorphology, and laccase production--of 442 strains were tested after 48-h and then after 3-year storage in liquid nitrogen using a perlite protocol (PP). All (100%) of them survived successfully both 48-h storage and 3-year storage in liquid nitrogen without noticeable growth and morphological changes. Also laccase production was unchanged. The viability and laccase production of a part (250) of these strains were compared with those of the strains subjected to an original agar plug protocol (OP). Using OP, 144 strains (57.6%) out of 250 survived a 3-year storage in liquid nitrogen. The results indicate that the cryopreservation protocol used significantly influences survival of the strains. Markedly better results were achieved using the PP.     

The Effect of Spatial Distributions of Mycoparasites on Biocontrol Efficacy: a Modelling Approach

The spatial distribution of propagules in soil is an important factor in determining the ability of mycoparasites to control soilborne plant pathogens. The assumptions of uniform, random and aggregated propagule distribution were used to evaluate the importance of spatial distribution patterns of propagules of a mycoparasite. For the random and uniform cases explicit expressions were obtained for the average distance between propagules. Average distances among propagules are 40-50% smaller for the random compared to the uniform distribution. For the aggregated case no explicit expression is possible and numerical simulations were used to generate spatial distributions. The consequences for host inactivation by the mycoparasite were evaluated using a simple model of omnidirectional and constant growth of the mycoparasite. A random distribution of propagules gave a considerably slower rate of inactivation than the uniform distribution. Numerical simulations were made to generate comparable patterns of host inactivation for aggregated distributions in which propagule clusters were located at random in three-dimensional space and the distances between propagules with centres followed a normal distribution. The number of propagule centres and propagules/centre varied for a given inoculum density. Parameters were estimated from published data for sclerotia of Sclerotium minor inactivation at different densities of macroconidia of Sporidesmium sclerotivorum. Differences in host inactivation between the uniform and random distributions were small but both gave poor predictions of the field data at low and high densities. The aggregated distribution gave an improved fit for the higher propagule densities but no improvement at the lower. In studying the dynamics of mycoparasites it may be more significant epidemiologically to design treatments based on differences in mean distances between propagules rather than population densities. Density-dependent effects on growth rate need more attention in models and studies on mycoparasite ecology.     

Crystal Structures of Phosphoketolase: THIAMINE DIPHOSPHATE-DEPENDENT DEHYDRATION MECHANISM*

Thiamine diphosphate (ThDP)-dependent enzymes are ubiquitously present in all organisms and catalyze essential reactions in various metabolic pathways. ThDP-dependent phosphoketolase plays key roles in the central metabolism of heterofermentative bacteria and in the pentose catabolism of various microbes. In particular, bifidobacteria, representatives of beneficial commensal bacteria, have an effective glycolytic pathway called bifid shunt in which 2.5 mol of ATP are produced per glucose. Phosphoketolase catalyzes two steps in the bifid shunt because of its dual-substrate specificity; they are phosphorolytic cleavage of fructose 6-phosphate or xylulose 5-phosphate to produce aldose phosphate, acetyl phosphate, and H₂O. The phosphoketolase reaction is different from other well studied ThDP-dependent enzymes because it involves a dehydration step. Although phosphoketolase was discovered more than 50 years ago, its three-dimensional structure remains unclear. In this study we report the crystal structures of xylulose 5-phosphate/fructose 6-phosphate phosphoketolase from Bifidobacterium breve. The structures of the two intermediates before and after dehydration (α,β-dihydroxyethyl ThDP and 2-acetyl-ThDP) and complex with inorganic phosphate give an insight into the mechanism of each step of the enzymatic reaction.     

Unusual Structures in the Flagellar Apparatus of a Strain of Trypanosoma cruzi*

Certain structures, associated with the flagellum, and which had hitherto been described as appearing occasionally in some species of trypanosomes, were found very frequently in epimastigote forms of strain F of Trypanosoma cruzi: (a) a group of tubular elements in an electron-dense mass enclosed within a swelling of the flagellar membrane as the flagellum emerges from its reservoir; (b) an expansion of the flagellar membrane at the point of the above swelling, which in cross-sections appears as a ring; and (c) an electron dense band in the body of the organism alongside the border of the flagellar pocket. The possible significance of these structures and the fact that so far they have been found only in one strain of T. cruzi are discussed.     

The biology of the stoat (Mustela erminea) in the National Parks of New Zealand VI. Infestation with Skrjabingylus nasicola

Abstract

The natural distribution of the parasite Skrjabingylus nasicola was surveyed in 1492 stoats from New Zealand’s National Parks. Infestation was rare in the young, so distribution was expressed as frequency of occurrence of skulls containing nematodes in samples of stoats more than 6 months old. Conservative estimates of incidence ranged from 0 to 37% in 27 local subsamples with at least 6 adults and subadults (mean 10%, n = 1005), sometimes varying substantially across short distances. Incidence was highest in beech forest and scrub/grassland habitats with annual rainfall less than 1600 mm. Subadult males (6–10 months old) were infested as frequently as adult males (older than 10 months), and there was no difference in incidence between the sexes. Worms recovered from 97 infested stoats occurred equally often in either side of the skull; were more often large (i.e., probably female) at all intensities of infestation; and numbered 1–73 per infested stoat (mean 12.9 in females, 14.2 in males; difference not significant). There was no evidence that infested stoats were smaller or lighter than uninfested onces.     

Bacterial Enrichment at the Gas-Water Interface of a Laboratory Apparatus

The gas-water interface (GWI) is likely to have important effects on bacterial adsorption and transport in unsaturated porous media. A glass apparatus that isolated GWIs in ports above a flowthrough suspension of a groundwater bacterial isolate was used to represent unsaturated porous media. The surface microlayer was collected by placing a polycarbonate filter on the GWI. The filter was stained, and the bacteria were enumerated by direct count. The significance of five independent variables on the surface density of cells (s, in cells per square millimeter) was determined by nonlinear multiple regression. Three of the variables were shown to be significant: surfactant concentration (d), time (t), and bulk bacterial concentration (B). The surface density decreased with increasing d and increased with increasing t and B. When surfactant was absent, the GWI became highly enriched in bacteria. For example, when d = 0, 48 h < t < 72 h, and 5,000 cells mm(sup-3) < B < 10,000 cells mm(sup-3), s averaged 3.0 x 10(sup4) cells mm(sup-2). This surface density occupied about 6.0% of the GWI, and the surface microlayer concentration of cells was 190 times the bulk concentration. The other two variables: pH (p) and ionic strength (I) were shown to be insignificant. The strong effect of d and the lack of effect of I and p support the hypothesis that hydrophobic interaction dominates bacterial adsorption to the GWI.     

Bioflavonoid Rescue of Ascorbate at a Membrane Interface

In aqueous solution, ascorbate potently prevents bleaching of cytochrome c on exposure to excess H₂O₂ or t-butyl hydroperoxide. Ascorbate failed to protect cytochrome c in the presence of liposomes of mitochondrial membranelike composition. Like the redox mediator N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), however, the bioflavonoids epicatechin and quercetin restored the protection afforded by ascorbate in the presence of liposomes and gave further protection. The quercetin glycoside, rutin, was much less effective, as was the vitamin E analog Trolox. In the presence of liposomes, quercetin alone was relatively ineffective, but cooperated with ascorbate to extend protection synergistically. The results bear specific implications in antioxidant protection of cytochrome c and in moderation of its hydroperoxidase activities in biological membranes. The data also reveal a situation where ascorbate is without effect except in the presence of a bioflavonoid, and substantiate a possibly vital role for certain bioflavonoids in mediating electron transfer from ascorbate into a hydrophobic environment.     

Parasitism of arbuscular mycorrhizal fungi: reviewing the evidence.

In order to understand the functioning of mycorrhizal fungi in ecosystems it is necessary to consider the full suite of possible biotic interactions in the soil. While a number of such interactions have recently been shown to be crucially important, parasitism is a highly neglected feature in the ecology of arbuscular mycorrhizal fungi (AMF). A number of studies have classified some interactions between populations of bacteria and fungi with AMF as parasitism, generating discussion about its consequences at both 'parasite' and host population levels. This paper reviews these various publications, and based on a set of criteria that are necessary to demonstrate parasitism, it was concluded that parasitism has not been conclusively shown to exist in AMF, even though some data are highly suggestive of such a relationship. The difficulties in gathering data supportive of parasitism were discussed, and hypotheses for defense were offered. This paper concludes by presenting potential consequences of AMF parasitism at the population/community levels and by discussing applied aspects.     

Connexin Channels at the Glio-Vascular Interface: Gatekeepers of the Brain

Neuronal survival, electrical signaling and synaptic activity require a well-balanced micro-environment in the central nervous system. This is achieved by the blood–brain barrier (BBB), an endothelial barrier situated in the brain capillaries, that controls near-to-all passage in and out of the brain. The endothelial barrier function is highly dependent on signaling interactions with surrounding glial, neuronal and vascular cells, together forming the neuro-glio-vascular unit. Within this functional unit, connexin (Cx) channels are of utmost importance for intercellular communication between the different cellular compartments. Connexins are best known as the building blocks of gap junction (GJ) channels that enable direct cell–cell transfer of metabolic, biochemical and electric signals. In addition, beyond their role in direct intercellular communication, Cxs also form unapposed, non-junctional hemichannels in the plasma membrane that allow the passage of several paracrine messengers, complementing direct GJ communication. Within the NGVU, Cxs are expressed in vascular endothelial cells, including those that form the BBB, and are eminent in astrocytes, especially at their endfoot processes that wrap around cerebral vessels. However, despite the density of Cx channels at this so-called gliovascular interface, it remains unclear as to how Cx-based signaling between astrocytes and BBB endothelial cells may converge control over BBB permeability in health and disease. In this review we describe available evidence that supports a role for astroglial as well as endothelial Cxs in the regulation of BBB permeability during development as well as in disease states.     

Influence of muskmelon cell wall polysaccharides on roridin E production by a pathogenic strain of Myrothecium roridum

Addition of fruit cell wall extracts from two muskmelon cultivars into liquid media affected mycotoxin production by a strain of Myrothecium roridum pathogenic to muskmelon. Cell wall extracts from a susceptible cultivar (Iroquois) significantly increased toxin production while cell wall extracts from a resistant cultivar (Hales Best) significantly inhibited toxin production. Media containing 0.1 or 1.0 mg ml^–1 stimulated toxin production more than media containing 10 or 100 mg ml^–1 of cell wall extracts. Previous studies in our laboratory suggest that roridin E may be involved in virulence or pathogenicity of M. roridum; the present study indicates that cell wall polysaccharides as well as other materials present in cell wall preparations from susceptible host tissue provide a better substrate for toxin production than cell wall preparation from resistant host tissue.