Host specificity dynamics: observations on gyrodactylid monogeneans

The directly transmitted viviparous gyrodactylids have high species richness but low morphological and biological diversity, and many species are recorded from only a single host. They therefore constitute a guild of species ideal for studies of the evolutionary significance of host specificity. The group has the widest host range of any monogenean family, being found on 19 orders of bony fish. However, individual species range from narrowly specific (71% of 402 described species recorded from a single host) to extremely catholic (Gyrodactylus alviga recorded from 16 hosts). Gyrodactylid-host interactions extend from 60 mya (G. lotae, G. lucii) down to 150 years (G. derjavini on Oncorhynchus mykiss). Co-evolution with the host is comparatively rare within the gyrodactylids, but host switching or ecological transfer is common, and has been facilitated by the mixing of fish strains that followed glaciation. In this review, we consider the factors responsible for gyrodactylid specificity patterns, using examples from our work on salmonid gyrodactylids including G. salaris, responsible for major epidemics on wild Atlantic salmon (Salmo salar) in Norway since 1975, and G. thymalli from grayling and G. derjavini from trout.G. salaris has a wide host range with highest population growth rates on Norwegian salmon strains. However, growth rates are variable on both host strains and species, because of the multitude of micro- and macro-environmental factors influencing parasite mortality and fecundity. A better predictor of performance is the proportion of fishes of a strain which are innately resistant to the parasite, a measure which is negatively correlated with the time to peak infection in a host strain. Population growth rate is also negatively correlated with age of infection; the initial rate, therefore, predicts best the suitability of a fish as host for G. salaris. The host response to gyrodactylids appears to be the same mechanism in all salmonids with innate resistance as one end of a spectrum, but influenced by stress and probably under polygenic control. Hybrid experiments show that performance of G. salaris on a host is heritable, and usually intermediate between that of the parents. This host response mechanism, coupled with the initial parasite population growth on a fish, determines the host specificity, i.e. whether the fish will be susceptible, a responder or innately resistant. The use of population growth rate parameters allows comparison of different hosts as a resource for a gyrodactylid. In the case of G. salaris, East Atlantic and Baltic strains of Atlantic salmon are core hosts, but other salmonids can physiologically sustain infections for considerable periods, and may be important in parasite dispersal and transmission. A further group of non-salmonid fishes are unable to sustain G. salaris reproduction, but can act as transport hosts.Population growth parameters are very labile to stressors and environmental factors, particularly temperature and salinity, and also other aspects of host ecology and water quality. These factors may also influence the spectrum of hosts that can be infected under particular conditions, and probably favoured ecological transfer of gyrodactylids between host species in periglacial conditions. G. salaris may still be undergoing post-glacial range expansion (aided by anthropogenic spread) as shown by the increase in the species range over the last 25 years. The origin of G. salaris, G. teuchis and G. thymalli is discussed in relation to glacial refugiums during the last ice age.     

beta-Glucanases from Candida albicans: purification, characterization and the nature of their attachment to cell wall components

beta-Glucanase activities were found associated with Candida albicans and their culture fluids. Mild acid treatment of the organisms led to rapid inactivation of beta-glucanase activities, the degree of loss increasing with the age of the cultures; the results suggested an extracytoplasmic location of the cell-associated enzymes. Most of the beta-glucanase activities were associated with the cell walls in organisms phenotypically resistant to amphotericin B methyl ester (AME). Two proteins (I and II) exhibiting beta-glucanase activity were isolated and purified by conventional procedures from cell-free extracts, cell-wall autolysates and culture fluids of C. albicans sensitive and phenotypically resistant to AME. The purified enzymes appeared homogeneous on isoelectric focusing, gel electrophoresis and ultracentrifugation, with molecular weights of 150000 (I) and 49000 (II). Both enzymes hydrolysed cell walls purified from AME-sensitive and phenotypically resistant organisms, but showed different substrate specificities and patterns of activity. Enzyme II hydrolysed (1 leads to 3)-beta-glycans by an endolytic mechanism releasing laminaritetraose as the initial product. Glucose was the only product released by enzyme I. The properties of th individual enzymes were unaffected by their localization or the age of the culture of the organisms. The loosening of the polysaccharide packing by ultrasonic treatment of cell walls purified from AME-resistant organisms increased the beta-glucanase activities bound to the walls, but did not solubilize them. Autolysis of cell walls released 58 to 66% of their beta-glucanase activity in 20 h, but no further release was attained on prolonged incubation. The amount of beta-glucanase activity released by autolysis was increased by a variety of pretreatments. Diethyl pyrocarbonate inhibited beta-glucanase activity and prevented autolysis. Evidence is presented indicating that interactions with lipids, polysaccharides and other cell wall proteins may be involved in the control of the activity of the cell wall-associated beta-glucanases in organisms phenotypically resistant to AME.     

Host bromeliads and their associated frog species: Further considerations on the importance of species interactions for conservation

Bromeliads constitute a good example of symbiosis with organisms that spend their entire life cycle inside the plants, and often depend on them to breed. The bromeliads benefit from this interaction by increasing their nutrients intake. Conservation efforts tend to focus on a single endangered species, but in symbiotic associations, the viability of one species depends on that of the other. Based on IUCN criteria, any species that depends on another to complete its life cycle should be assigned a conservation status equivalent to that of the host taxon, where appropriate. We gathered published plus fieldwork data on the frog-bromeliad mutualism and compiled a checklist of 99 bromeligenous frogs species associated to 69 bromeliad hosts, and found threatened bromeliads hosting non-threatened frogs. We found that 62% bromeligenous frogs inhabit unspecified bromeliads. Finally, we propose strategies for improving understanding and conservation of the frog-bromeliad mutualism.     

Microcins: their nature and genetic determination

A number of gram-negative bacteria are capable of synthesizing the low molecular mass antibiotics microcins, the substances with molecular masses up to 10 000 D possessing a broad range of antibiotic activity. The synthesis is not lethal for the producing cells and is not induced by DNA-damaging agents. The investigated microcins are either of oligopeptide nature or are analogues of methionine. Five types of microcins have been described. The A- and C-types of microcins inhibit protein synthesis, microcins B suppress DNA replication, microcins D and F affect cellular energy potential. Microcin synthesis and immunity to microcins are shown to be plasmid mediated. The role of microcins in ecology of enterobacteria and the ranking among bacterial antibiotics are discussed.     

Glyoxal oxidases: their nature and properties

H₂O₂ has been found to be required for the activity of the main microbial enzymes responsible for lignin oxidative cleavage, peroxidases. Along with other small radicals, it is implicated in the early attack of plant biomass by fungi. Among the few extracellular H₂O₂-generating enzymes known are the glyoxal oxidases (GLOX). GLOX is a copper-containing enzyme, sharing high similarity at the level of active site structure and chemistry with galactose oxidase. Genes encoding GLOX enzymes are widely distributed among wood-degrading fungi especially white-rot degraders, plant pathogenic and symbiotic fungi. GLOX has also been identified in plants. Although widely distributed, only few examples of characterized GLOX exist. The first characterized fungal GLOX was isolated from Phanerochaete chrysosporium. The GLOX from Utilago maydis has a role in filamentous growth and pathogenicity. More recently, two other glyoxal oxidases from the fungus Pycnoporus cinnabarinus were also characterized. In plants, GLOX from Vitis pseudoreticulata was found to be implicated in grapevine defence mechanisms. Fungal GLOX were found to be activated by peroxidases in vitro suggesting a synergistic and regulatory relationship between these enzymes. The substrates oxidized by GLOX are mainly aldehydes generated during lignin and carbohydrates degradation. The reactions catalysed by this enzyme such as the oxidation of toxic molecules and the production of valuable compounds (organic acids) makes GLOX a promising target for biotechnological applications. This aspect on GLOX remains new and needs to be investigated.     

In-silico prediction and observations of nuclear matrix attachment

The nuclear matrix is a functionally adaptive structural framework interior to the nuclear envelope. The nature and function of this nuclear organizer remains the subject of widespread discussion in the epigenetic literature. To draw this discussion together with a view to suggest a way forward we summarize the biochemical evidence for the modalities of DNA-matrix binding alongside the in-silico predictions. Concordance is exhibited at various, but not all levels. On the one hand, both the reiteration and sequence similarity of some elements of Matrix Attachment Regions suggest conservation. On the other hand, in-silico predictions suggest additional unique components. In bringing together biological and sequence evidence we conclude that binding may be hierarchical in nature, reflective of a biological role in replicating, transcribing and potentiating chromatin. Nuclear matrix binding may well be more complex than the widely accepted simple loop model. Invited paper All referenced websites were verified. URLs and their content are subject to change. The content referenced in this paper can be accessed using internet archive tools such as www.archive.org with the query restricted to November 2005.     

Biochemical genetics in the study of schistosomes and their intermediate hosts

This paper considers the contributions that studies on electrophoresis of enzymes have made to the understanding of the biology of schistosomiasis. The use of enzymes for characterisation of schistosomes is reviewed and particular attention is given to investigations concerning hybridisation, mating behaviour and population structure. Results are presented on variation between isolates of S. haematobium detected by analysis of a G6PDH polymorphism and variation of G6PDH and MDH-1 within natural populations of S. leiperi from lechwe in Zambia. Genetic variation of snail populations is considered in relation to susceptibility to schistosomes. Examples are given illustrating the ways in which inheritance studies can be used to investigate the breeding biology of snails.     

Babesia argentina: Studies on the nature of an antigen associated with infection

A crude soluble haemagglutination antigen obtained from a mixture of Babesia argentina parasites and infected erythrocyte stromata contained fibrinogen. The fibrinogen was removed by precipitation in an initial attempt to purify the antigen. However, most if not all of the antigenic activity was located in the fibrinogen precipitate. After consideration of the evidence available, it was concluded that the antigen was either a babesial moiety complexed with fibrinogen or a fibrinogen molecule altered by the metabolic activity of the parasite.     

Lytic activity from schistosomes: interactions with blood cells

1. The schistosome lytic agent hemolyzed animal red blood cells (RBCs) containing high concentrations of membrane phosphatidyl choline (dog, mouse, and rat) more efficiently than RBCs having no phosphatidyl choline (goat and sheep). 2. Human mononuclear cells lost viability in the presence of the schistosome lytic agent. 3. Preincubating the lytic agent with phosphatidyl choline or bovine serum albumin reduced its lytic activity. 4. Extracellular albumin protected the RBCs from schistosome induced hemolysis. 5. Pretreatment of the RBCs with various proteases enhanced lysis by 10-30%.     

Mitochondrial antigens: their presentation and related diseases

<正>Mitochondria produce energy and metabolic intermediates necessary for the survival of cells. They also play important roles in immunity. Emerging evidence has indicated that mitochondria can be involved in various diseases by triggering immune responses(Baum, 1995; Berg and Klein, 1986). Mitochondrial antigens(Mt Ags) refer to any substances derived from mitochondria that can be recognized by the adaptive immune system and cause immune responses.     

Diseases associated with specific HL-A antigens.

Significantly increased prevalences of particular HL-A antigens have been reported for many human diseases. The correlation is particularly striking in ankylosing spondylitis, Reiter''s syndrome, psoriasis and some immunopathic disorders, so that HL-A typing may be of great value in diagnosis. The possible mechanisms whereby these associations may occur suggest the cause of certain disorders, and further investiatation will likely help in the understanding of the pathogenesis of many diseases.