The symbiotic microflora associated with the tegument of proteocephalidean cestodes and the intestines of their fish hosts

The indigenous symbiotic microflora associated with the tegument of proteocephalidean cestodes and the intestines of their fish hosts has been investigated in morphological and ecological aspects. The indigenous microflora associated with the cestode tegument consists of the nannobacteria population, which was present obligatorily on the surface of tegument, and the "deep microflora". The deep microflora associates with some few species of parasites only. Each individual host-parasite micro-biocenosis includes specific indigenous symbiotic microorganisms, with the differing microfloras of host intestine and parasite. Physiology, biochemistry and/or diet of hosts apparently influence on the symbiotic microflora's structure of parasites. The least bacteria abundance and diversity of their morphotypes were observed in the parasites from baby fishes. The diversity and abundance of bacteria were increased with the fish host ageing and the formation of the definitive structure of its intestine. It is an evidence of the gradual invading of the intestinal parasites (cestodes) tegument by bacterial cells. The invading is realized on the base of the microflora that was present in the food of fish host. The symbiotic microflora has specific morphological features, can regulate the homeostasis of the cestodes and fish hosts and also can maintain equilibrium of alimentary and immune interrelations in the host-parasite system.     

Indigenous microflora associated with the tegument of Triaenophorus nodulosus (Cestoda) and the intestine of its pike host

Investigations of the indigenous microflora associated with the mucous intestines of fish and its cestode parasites have been for the first time carried out using the methods of transmission and scanning electron microscopy. New data on the bacterial biodiversity in the cestode and its fish host are obtained. Nanobacteria and spirochaetes are for the first time revealed in a fish host together with the previously known bacteria forming the intestinal microflora of fish. Spirochaetes were shown to be associated with the intestines of a pike host only, while nanobacteria cover abundantly the surface of the apical parts of the intestinal microvilli and the apical parts of the microtriches in the cestode tegument. The similarity of the bacterial floras associated with the apical surface of the parasite tegument and the intestine of the host should be noted. At the same time, deeper bacterial communities represented by obligate symbionts are specific. Thus, there is a normal indigenous microflora in cestodes, associated with the tegumental surface. This symbiotic microflora has specific morphological features and provides the balance of relations in the parasite-host system.     

Ecological approach to the problem of monophyly of Neodermata (Platyhelminthes)

The ecological scenario of the evolution of main branches of Neodermata is described. The first neodermateans (= promonogeneans) were parasites of the gill lamellae of Paleozoic jawless vertebrates, which were microphagous suspension-feeding animals. The main apomorphic characters of the primary neodermateans are neodermis, cercomer (posterior hooked attachment organ) and swimming infective larva. All subsequent evolution of Neodermata was related with their acquisition new niches in hosts, which were intensively diverging in that time adapting to new food types and conquering new ecological niches. The acquisition of new microhabitats was accompanied by the development of morphological diversity in Neodermata especially in a structure of attachment and genital organs. Trematoda, Cestoda and Polyopisthocotylea comprise specialized evolutionary lineages and Monopisthocotylea is a basal taxon. Polyopisthocotylea is specialized to the blood feeding on fish gills. The common ancestors of the Trematoda and Cestoda inhabited walls of gills and pharyngeal cavities, from where they penetrated the digestive tract. The aspidogastridean multiloculate hold fast appears to be a highly specialized attachment organ of the monogenean ancestor, which inhabited muscular pharyngeal walls of Paleozoic vertebrates. The loss of cercomer hooks probably took place when mollusk-hosts have been involved in the aspidogastridean life cycle. The extinction of many chondrichthiean groups and progress of small plankton fishes (Teleostei) has led to the appearance Digenea. New vertebrate hosts needed a new infestation type and the cercaria appeared. Parthenogenesis has been developed in stages living in mollusks to counterbalance the loss of individuals at two transmission stages in the digenean cycle; this was resulted in a strong specificity to mollusk-host. Evolutionary tendencies of Trematoda and Cestoda show noticeable similarities.     

Ultramicrobacteria: Formation of the concept and contribution of ultramicrobacteria to biology

Ultramicrobacteria (UMB) are species of the domain Bacteria characterized by very small sizes of proliferating cells (less than 0.1 μm³ in volume) and small genomes (3.2 to 0.58 Mb). Some authors use the term nanobacteria as a synonym of UMB. Several tens of UMB species have been isolated from various natural habitats: sea water, soil, silt, Greenland ice sheet, permafrost soils, and intestines of humans and insects. Under laboratory conditions, they are cultivated on different nutrient media. In the second prokaryotic domain, the Archaea, ultrasmall forms (ultramicroarchaea) have also been described, including nanoarchaea (members of the genus Nanoarchaeum) with a cell volume of less than 0.1 μm³. The term nanobacteria is used in the literature also to denote ultrasmall bacterium-like particles occurring in rocks, sands, soils, deep sub-surface layers, meteorites, and clinical samples. The systematic position and the capacity for self-reproduction of these particles are still unclear. The cultured UMB forms are characterized by highly diverse morphology, ultrastructural organization, physiology, biochemistry, and ecology. UMB form three groups according to the type of cell wall structure and the reaction to Gram staining: (1) gram-negative, (2) gram-positive, and (3) cell wall-lacking. Their cells divide by constriction, septation, or budding. The unique processes performed by UMB are dehalorespiration and obligate or facultative epibiotic parasitism. The UMB that synthesize organic compounds in ocean waters with the involvement of proteorhodopsin play a great role in the biosphere. UMB have been found in seven large phylogenetic groups of prokaryotes, where their closest relatives are organisms with larger cells typical of bacteria, which is evidence of the polyphyletic origin of the currently known UMB species and the reductive mode of their evolution.     

Ultrastructure adaptations of symbiotic bacteria associated with freshwater fish and their cestode parasites

The ultrastructure of symbiotic bacteria colonizing the mucous membrane of the gut of freshwater fish and the tegument surface of their cestodes was studied. A comparative analysis of published and original data made it possible to define the ultrastructure peculiarities promoting the adaptation of bacteria to the digestive transport surfaces of fish and their intestinal parasites. The studied peculiarities may be split into three groups: (1) the structure and composition of the bacterial cell surface, which allows the colonization of gut epithelia and cestode tegument; (2) the intracellular ultrastructure of the bacteria; and (3) the reorganization of cell types, i.e., the formation of the dormant cells and nanobacteria.     

Morphological and ultrastructural characteristics of symbiotic bacteria colonizing the surface of the helminth Triaenophorus nodulosus and the intestine of pike Esox lucius

The microflora inhabiting the intestinal mucosa of the pike and the tegument surface of the intestinal parasite Triaenophorus nodulosus is investigated. By means of electron microscopy, the ultrastructural features of bacteria and pattern of their interaction with the colonized surfaces are estimated. Specific distribution of microorganisms belonging to different morphotypes and subdivided into subpopulations on the colonized surfaces is found. Predominance of gram-negative bacteria in all studied microbiocenoses and abundance of nanobacteria in the “superficial” subpopulations are observed. The bacteria of “a deep population” associated with the basal parts of microtrichiae and microvilli are described. It is concluded that the helminthes, the fish parasites possess the normal microflora characterized by specific composition, by ultrastructural features of cells, and by patterns of interaction with the helminth surface. The obtained data characterize the mechanisms of symbiotic interaction of prokaryotes and eukaryotes in the system parasite-host-symbiotic microflora.     

Parasites of forage fishes in the vicinity of Steller sea lion (Eumetopias jubatus) habitat in Alaska

Fish serve as intermediate hosts for a number of larval parasites that have the potential of maturing in marine mammals such as Steller sea lions (Eumetopias jubatus). We examined the prevalence of parasites from 229 fish collected between March and July 2002 near two islands used by Steller sea lions in Southeast Alaska and island habitats in the Aleutian Islands. Sea lion populations have remained steady in Southeast Alaska but have been declining over the last 30 yr in the Aleutian Islands. Even though the fish samples near the Southeast Alaska haul-outs were composed of numerous small species of fish and the Aleutian Islands catch was dominated by juveniles of commercially harvested species, the parasite fauna was similar at all locations. Eleven of the 20 parasite taxa identified were in their larval stage in the fish hosts, several of which have been described from mammalian final hosts. Four species of parasite were more prevalent in Southeast Alaska fish samples, and seven parasite species, including several larval forms capable of infecting marine mammals, were more prevalent in fish from the Aleutian Islands. Nevertheless, parasites available to Steller sea lions from common fish prey are not likely to be a major factor in the decline of this marine mammal species.     

Primordial proteins and HIV

Primordial proteins regulate the response of nanobacteria to variations in their environment and reinforce existing pathogenic potentials. By analyzing specific response patterns, we predicted the prevalence of nanobacteria in HIV--and in the atmosphere. A current clinical study indicates the identification of a possibly giant nanobacterial reservoir in Africa: a significant fraction of a test group (40 HIV-infected mothers and 13 babies) was infected with nanobacteria. Concurrently, a multitude of 80-300 nm nanovesicles, apparently nanobacteria, were detected in the atmosphere of the Earth. Nanobacterial infections in HIV are possibly comparable to the twin epidemics HIV and tuberculosis. Models inspired by proteomics recommend methods to inactivate nanobacteria (and other slime-producing bacteria) in the body.     

An alternative origin for nanobacteria in kidney stones

Small (50–200 nm), calcium phosphate (apatite)-covered organic particles called nanobacteria or calcifying nanoparticles (CNP) seem to be ubiquitous in kidney stones and are thought to be involved in stone formation. Although initial claims that these particles are the smallest known life forms have been somewhat softened, much controversy remains as to their involvement in kidney stone formation as well as in other pathological calcifications. I suggest that such particles are non-living and may be formed during the normal living activities of bona-fide bacteria which inhabit the kidneys. This hypothesis is based on previous observations that bacteria immersed in a supersaturated fluid produce organic globules which calcify when released to the surrounding fluid, forming CNP-like particles. The possibility that this process is responsible for the formation of CNP associated with pathological calcifications deserves greater scrutiny.     

Environmental and ecological factors that shape the gut bacterial communities of fish: a meta-analysis

Symbiotic bacteria often help their hosts acquire nutrients from their diet, showing trends of co-evolution and independent acquisition by hosts from the same trophic levels. While these trends hint at important roles for biotic factors, the effects of the abiotic environment on symbiotic community composition remain comparably understudied. In this investigation, we examined the influence of abiotic and biotic factors on the gut bacterial communities of fish from different taxa, trophic levels and habitats. Phylogenetic and statistical analyses of 25 16S rRNA libraries revealed that salinity, trophic level and possibly host phylogeny shape the composition of fish gut bacteria. When analysed alongside bacterial communities from other environments, fish gut communities typically clustered with gut communities from mammals and insects. Similar consideration of individual phylotypes (vs. communities) revealed evolutionary ties between fish gut microbes and symbionts of animals, as many of the bacteria from the guts of herbivorous fish were closely related to those from mammals. Our results indicate that fish harbour more specialized gut communities than previously recognized. They also highlight a trend of convergent acquisition of similar bacterial communities by fish and mammals, raising the possibility that fish were the first to evolve symbioses resembling those found among extant gut fermenting mammals.     

Putative Phage Hyperparasite in the Rickettsial Pathogen of Abalone, “Candidatus Xenohaliotis californiensis”

Studies on the ecology of microbial parasites and their hosts are predicated on understanding the assemblage of and relationship among the species present. Changes in organismal morphology and physiology can have profound effects on host–parasite interactions and associated microbial community structure. The marine rickettsial organism, “Candidatus Xenohaliotis californiensis” (WS-RLO), that causes withering syndrome of abalones has had a consistent morphology based on light and electron microscopy. However, a morphological variant of the WS-RLO has recently been observed infecting red abalone from California. We used light and electron microscopy, in situ hybridization and16S rDNA sequence analysis to compare the WS-RLO and the morphologically distinct RLO variant (RLOv). The WS-RLO forms oblong inclusions within the abalone posterior esophagus (PE) and digestive gland (DG) tissues that contain small rod-shaped bacteria; individual bacteria within the light purple inclusions upon hematoxylin and eosin staining cannot be discerned by light microscopy. Like the WS-RLO, the RLOv forms oblong inclusions in the PE and DG but contain large, pleomorphic bacteria that stain dark navy blue with hematoxylin and eosin. Transmission electron microscopy (TEM) examination revealed that the large pleomorphic bacteria within RLOv inclusions were infected with a spherical to icosahedral-shaped putative phage hyperparasite. TEM also revealed the presence of rod-shaped bacteria along the periphery of the RLOv inclusions that were morphologically indistinguishable from the WS-RLO. Binding of the WS-RLO-specific in situ hybridization probe to the RLOv inclusions demonstrated sequence similarity between these RLOs. In addition, sequence analysis revealed 98.9–99.4 % similarity between 16S rDNA sequences of the WS-RLO and RLOv. Collectively, these data suggest that both of these RLOs infecting California abalone are “Candidatus Xenohaliotis californiensis,” and that the novel variant is infected by a putative phage hyperparasite that induced morphological variation of its RLO host.     

Variation in stickleback head morphology associated with parasite infection

Parasites can affect host phenotypes, influencing their ecology and evolution. Host morphological changes occurring post-infection might result from pathological by-products of infection, or represent adaptations of hosts or parasites. We investigated the morphology of three-spined sticklebacks, Gasterosteus aculeatus , from a population naturally infected with Schistocephalus solidus , which grows to large sizes in their body cavity. We examined local effects of infection on trunk shape, which are imposed directly by the bulk of the growing parasite, and distant effects on head morphology. We show that trunk shape differed between infection classes, and was affected more severely in fish with heavier total parasite mass. We further show unexpected differences in head morphology. The heads of infected fish were reduced in size and differently shaped to those of non-infected fish, with infected fish having deeper heads. Importantly, both head size and shape were also affected more severely in fish with heavier total parasite mass. This latter result suggests that differences in morphology are caused by post-infection changes. Such changes may be incidental, evolutionarily neutral 'side effects' of infection. However, because head morphology affects foraging ecology, such changes are likely to have fitness consequences for hosts, and may constitute adaptations, either of hosts or of parasites. We discuss our finding in the context of the evolution of phenotypic plasticity, and suggest testable hypotheses examining the proximate mechanisms underlying these morphological effects and their potential evolutionary basis.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 759–768.     

Iron, infection, and neoplasia

In nearly all forms of life, the number and diversity of enzymes that contain iron or that depend on the presence of this metal for activity are impressive. Not surprisingly, chemical mechanisms have been evolved by many organisms that permit them to solubilize and acquire iron while at the same time depriving their competitors or their pathogens of this element. Proteins such as transferrin and lactoferrin that are employed by vertebrate hosts for iron transport and acquisition can, to some extent, withhold the metal from the siderophores of invading bacteria and fungi. Attempts also are made by animal hosts to withhold iron from protozoa and neoplastic cells. Unfortunately, pathogenic microorganisms have developed a variety of counter measures that are especially dangerous in hosts stressed by iron overload in specific fluids, tissues, or cells. In recent years, however, a number of possible methods and agents for strengthening iron-withholding defense have become apparent. Nearly 3,000 papers on various aspects of iron withholding are contained in the 18-year Medline Database and numerous reviews have been published since 1966. The present paper will focus on developments that have been reported within the past 2 1/2 years.     

Nanobacteria are mineralo fetuin complexes

"Nanobacteria" are nanometer-scale spherical and ovoid particles which have spurred one of the biggest controversies in modern microbiology. Their biological nature has been severely challenged by both geologists and microbiologists, with opinions ranging from considering them crystal structures to new life forms. Although the nature of these autonomously replicating particles is still under debate, their role in several calcification-related diseases has been reported. In order to gain better insights on this calciferous agent, we performed a large-scale project, including the analysis of "nanobacteria" susceptibility to physical and chemical compounds as well as the comprehensive nucleotide, biochemical, proteomic, and antigenic analysis of these particles. Our results definitively ruled out the existence of "nanobacteria" as living organisms and pointed out the paradoxical role of fetuin (an anti-mineralization protein) in the formation of these self-propagating mineral complexes which we propose to call "nanons." The presence of fetuin within renal calculi was also evidenced, suggesting its role as a hydroxyapatite nucleating factor.     

Parasitism of Molluscs by Nematodes: Types of Associations and Evolutionary Trends

Although there are no confirmed fossil records of mollusc parasitic nematodes, diverse associations of more than 108 described nematode species with slugs and snails provide a fertile ground for speculation of how mollusc parasitism evolved in nematodes. Current phylogenic resolution suggests that molluscs have been independently acquired as hosts on a number of occasions. However, molluscs are significant as hosts for only two major groups of nematodes: as intermediate hosts for metastrongyloids and as definitive hosts for a number of rhabditids. Of the 61 species of nematodes known to use molluscs as intermediate hosts, 49 belong to Metastrongyloidea (Order Strongylida); of the 47 species of nematodes that use molluscs as definitive hosts, 33 belong to the Order Rhabditida. Recent phylogenetic hypotheses have been unable to resolve whether metastrongyloids are sister taxa to those rhabditids that use molluscs as definitive hosts. Although most rhabditid nematodes have been reported not to kill their mollusc hosts prior to their reproduction, some species are pathogenic. In fact, infective juveniles of Phasmarhabditis hermaphrodita vector a lethal bacterium into the slug host in which they reproduce. This life cycle is remarkably similar to the entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae. Also, the discoveries of Alloionema and Pellioditis in slugs are interesting, as these species have been speculated to represent the ancestral forms of the entomopathogenic nematodes. Development of the infective stage appears to be an important step toward the acquisition of molluscs as definitive hosts, and the association with specific bacteria may have arisen in conjunction with the evolution of necromeny.     

Characterization of 'Candidatus Clavochlamydia salmonicola': an intracellular bacterium infecting salmonid fish

The phylum Chlamydiae contains obligate intracellular bacteria, several of which cause disease in their hosts. Morphological studies have suggested that this group of bacteria may be pathogens of fish, causing cysts in epithelial tissue – epitheliocystis. Recently, the first genetic evidence of a chlamydial aetiology of this disease in seawater reared Atlantic salmon from Norway and Ireland was presented, and the agent was given the name ' Candidatus Piscichlamydia salmonis'. In this article we present molecular evidence for the existence of a novel Chlamydiae that also may cause epitheliocystis in Norwegian salmonids. This novel Chlamydiae has been found in salmonid fish from freshwater, and based on its partial 16S rRNA gene, it may constitute a third genus in the family Chlamydiaceae , or a closely related sister family. By using whole-mount RNA–RNA hybridization we demonstrate how infected cells are distributed in a patchy manner on a gill arch. The morphology of the novel Chlamydiae includes the characteristic head-and-tail cells that have been described earlier from salmonid fish suffering from epitheliocystis. We propose the name ' Candidatus Clavochlamydia salmonicola' for this agent of epitheliocystis in freshwater salmonids.     

Predators shape distribution and promote diversification of morphological defenses in <Emphasis Type="Italic">Leucorrhinia</Emphasis>, Odonata

Predators strongly influence species assemblages and shape morphological defenses of prey. Interestingly, adaptations that constitute effective defenses against one type of predator may render the prey susceptible to other types of predators. Hence, prey may evolve different strategies to escape predation, which may facilitate adaptive radiation of prey organisms. Larvae of different species in the dragonfly genus Leucorrhinia have various morphological defenses. We studied the distribution of these larvae in relation to the presence of predatory fish. In addition, we examined the variation in morphological defenses within species with respect to the occurrence of fish. We found that well-defended species, those with more and longer spines, were more closely associated with habitats inhabited by predatory fish and that species with weakly developed morphological defenses were more abundant in habitats without fish. The species predominantly connected to lakes with or without fish, respectively, were not restricted to a single clade in the phylogeny of the genus. Our data is suggestive of phenotypic plasticity in morphological defense in three of the studied species since these species showed longer spines in lakes with fish. We suggest that adaptive phenotypic plasticity may have broadened the range of habitats accessible to Leucorrhinia. It may have facilitated colonization of new habitats with different types of predators, and ultimately, speciation through adaptive radiation.     

Multivariate analyses of metrical features in the Lepidapedon elongatum (Lebour, 1908) species-complex (Digenea,Lepocreadiidae) in deep and shallow water gadiform fishes of the NE Atlantic

One hundred and eleven Lepidapedon elongatum-like worms from five gadiform fish species in the North Atlantic are compared using multivariate analyses of 22 metrical features. A principal component analysis followed by a discriminant analysis indicate multivariate morphological differences between worms in the different hosts. It is argued that the forms in the five host species, Gadus morhua, Onogadus argentatus, Trachyrhynchus trachyrhynchus, Coryphaenoides (Nematonurus) armatus and Lepidion eques, should be considered separate oioxenic species.     

Post-Viking Microbiology: New Approaches,New Data,New Insights

In the 20 years since the Viking experiments, major advances have been made in the areas of microbial systematics, microbial metabolism, microbial survival capacity, and the definition of environments on earth, suggesting that life is more versatile and tenacious than was previously appreciated. Almost all niches on earth which have available energy, and which are compatible with the chemistry of carbon-carbon bonds, are known to be inhabited by bacteria. The oldest known bacteria on earth apparently evolved soon after the formation of the planet, and are heat loving, hydrogen and/or sulfur metabolizing forms. Among the two microbial domains (kingdoms) is a great deal of metabolic diversity, with members of these forms being able to grow on almost any known energy source, organic or inorganic, and to utilize an impressive array of electron acceptors for anaerobic respiration. Both hydrothermal environments and the deep subsurface environments have been shown to support large populations of bacteria, growing on energy supplied by geothermal energy, thus isolating these ecosystems from the rest of the global biogeochemical cycles. This knowledge, coupled with new insights into the history of the solar system, allow one to speculate on possible evolution and survival of life forms on Mars.