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排序方式: 共有144条查询结果,搜索用时 859 毫秒
1.
Dr. V. Benno Meyer-Rochow 《Cell and tissue research》1978,186(2):337-349
Summary In Streetsia challengeri left and right eyes have fused and become a single cylindrical photoreceptor, which occupies the basal half of a forward directed head projection. This unusual compound eye consists of approximately 2500 ommatidia, which are arranged in such a way that the animal has almost circumferential vision, but cannot look ahead or behind. It is thought that the eye operates on light-guide principles, and that the crystalline cones are the major dioptric component. Ommatidia in anterior-posterior rows show a greater overlap of visual fields than dorso-ventrally arranged ommatidia. Cone layer and retinula are separated by a 4 m thick screen-membrane, which contains tiny pigment granules of 0.15 m diameter. Cells of unknown function and origin, containing unusual multitubular organelles, are regularly found near the proximal ends of the crystalline cone threads. The twisted rhabdoms measure 18–20 m in diameter, and consist of microvilli 0.05 m in width, which belong to five retinula cells and which show no trace of disintegration. The position of interommatidial screening pigment, the density of retinula cell vesicles and inclusions, and the narrowness of the perirhabdomal space all suggest that the eyes have been light-adapted at the time of fixation for electron microscopy. The retinula cell nuclei lie on the proximal side of the heavily pigmented basement membrane. A tapetum or basal retinula cells are not developed. It is concluded that the eye optimally combines acuity with sensitivity, and that for distance estimation parallax may be important.Address until January 25th 1978: Scott Base, Ross Dependency, Antarctica (C/-Chief Post Office, Christchurch, New Zealand) 相似文献
2.
The dark ocean and the underlying deep seafloor together represent the largest environment on this planet, comprising about 80% of the oceanic volume and covering more than two-thirds of the Earth's surface, as well as hosting a major part of the total biosphere. Emerging evidence suggests that these vast pelagic and benthic habitats play a major role in ocean biogeochemistry and represent an “untapped reservoir” of high genetic and metabolic microbial diversity. Due to its huge volume, the water column of the dark ocean is the largest reservoir of organic carbon in the biosphere and likely plays a major role in the global carbon budget. The dark ocean and the seafloor beneath it are also home to a largely enigmatic food web comprising little-known and sometimes spectacular organisms, mainly prokaryotes and protists. This review considers the globally important role of pelagic and benthic protists across all protistan size classes in the deep-sea realm, with a focus on their taxonomy, diversity, and physiological properties, including their role in deep microbial food webs. We argue that, given the important contribution that protists must make to deep-sea biodiversity and ecosystem processes, they should not be overlooked in biological studies of the deep ocean. 相似文献
3.
Alvinella pompejana, the so-called Pompeii worm (Desbruyères and Laubier, 1980), is found exclusively in association to high temperature venting,
at the surface of hydrothermal chimneys of the East Pacific Rise. The main characteristics of this emblematic species is its
tolerance to high temperature but its ability to colonize extremely hot substrates has been the subject of much controversy.
In the last decade, new tools allowing in situ and in vivo investigation have been determinant in the understanding of the
strategies and adaptations required to colonize such an extremely hot environment. New data relative to the characterization
of the animal habitat conditions, on one hand, to the molecular adaptations of this organism and the colonization processes
by this species, on the other hand, are now available. Advanced methods and tools, that have fostered the physico-chemical
characterization of vent habitats in recent years, are first reviewed. Factors controlling the physico-chemical variability
of vent habitats and the threats A. pompejana might effectively face are discussed. The exceptional thermotolerance of this species and the maximum temperature it could
sustain are then considered in the light of molecular data relative to its collagen stability. Life history traits as well
as biological controls on tube micro-habitat conditions are discussed on the basis of new in situ and in vivo experiments
and characterization. Finally, the current knowledge and opened questions related to the molecular adaptations to chemical
stresses are briefly stated. The ability of Alvinella pompejana to colonize these substrates is far from being fully understood, but the exceptional properties of its extracellular biopolymers
and the behavior of the worm can be now considered as major clues in the colonization process. Alvinella pompejana could thus stand at the limits authorized for its biological machinery in a highly dynamic environment where temperature
can readily reach lethal values, but where temperature regulation by the animal itself would prevent exposure to deleterious
thermal spikes. The dynamic system associating this pioneer species and its associated microflora might be viewed as a key
to the subsequent colonization of these environments by less tolerant species, highlighting A. pompejana as a new type of ecosystem bioengineer. 相似文献
4.
Kanamasa S Sumi K Yamuki N Kumasaka T Miura T Abe F Kajiwara S 《Molecular genetics and genomics : MGG》2007,277(4):403-412
5.
Lithocarols A-F (1–6) possessing novel highly-oxygenated isobenzofuran core, together with a related known compound isoprenylisobenzofuran A (7) were isolated from the marine-derived fungus Phomopsis lithocarpus FS508. Among them, lithocarols A-E (1–5) represent the first examples of poly-ketal derivatives in tenellone family. The structures for all these compounds were fully elucidated by spectroscopic analysis, X-ray diffraction, and electronic circular dichroism calculations. Their cytotoxic assay disclosed that compounds 1–4 displayed moderate growth inhibitory effect against four human tumor cell lines with the IC50 values ranging from 10.5 to 38.7 μM. 相似文献
6.
Grote R Li L Tamaoka J Kato C Horikoshi K Antranikian G 《Extremophiles : life under extreme conditions》1999,3(1):55-62
A novel coccoid-shaped, hyperthermophilic, anaerobic archaeon, strain RG-20, was isolated from a deep-sea hydrothermal vent
fluid sample taken at 1394-m depth at the Mid-Okinawa Trough (27°32.7′N, 126°58.5′E). Cells of this isolate occur singly or
in pairs and are about 0.8 to 2 μm in diameter. Growth was observed at temperatures between 50° and 93°C, with an optimum
at 85°C. The pH range for growth is 5.0–9.0, with an optimum around 7.0. Strain RG-20 requires 1%–4% of NaCl for growth, and
cell lysis occurs at concentrations below 1%. The newly isolated strain grows preferentially in the presence of elemental
sulfur on proteinaceous substrates such as yeast extract, peptone, or tryptone, and no growth was observed on carbohydrates,
carboxylic acids, alcohols, or lipids. This microorganism is resistant to streptomycin, chloramphenicol, ampicillin, and kanamycin
at concentrations up to 150 μg/ml, but is susceptible to rifampicin. Analysis of the hydrolyzed core lipids by thin-layer
chromatography (TLC) revealed the presence of archaeol and caldarchaeol. The mol% G+C content of the DNA is 55.8. Partial
sequencing of the 16S rDNA indicates that strain RG-20 belongs to the genus Thermococcus. Considering these data and on the basis of the results from DNA-DNA hybridization studies, we propose that this strain should
be classified as a new species named Thermococcus siculi (si′cu.li. L. gen. n. siculi, of the deep-sea [siculum, deep-sea in literature of Ovid], referring to the location of the sample site, a deep-sea hydrothermal vent). The type strain
is isolate RG-20 (DSM No. 12349).
Received: May 11, 1998 / Accepted: July 24, 1998 相似文献
7.
Asbestopluma hypogea
(Porifera) is a carnivorous species that belongs to the deep-sea taxon Cladorhizidae but lives in littoral caves and can be raised easily in an aquarium. It passively captures its prey by means of filaments covered with hook-like spicules. Various invertebrate species provided with setae or thin appendages are able to be captured, although minute crustaceans up to 8 mm long are the most suitable prey. Transmission electron microscopy observations have been made during the digestion process. The prey is engulfed in a few hours by the sponge cells, which migrate from the whole body towards the prey and concentrate around it. A primary extracellular digestion possibly involving the activity of sponge cells, autolysis of the prey and bacterial action results in the breaking down of the prey body. Fragments of the prey, including connective cells and muscles, are then phagocytosed and digested by archaeocytes and bacteriocytes. The whole process takes 8–10 days for a large prey. This unique feeding habit implies the capture and digestion of a macro-prey without any digestive cavity. It would appear to be an adaptation to life in deep-sea oligotrophic environments. Carnivorous sponges provide actual evidence, through a functional example, that a transition is possible from the filter-feeder poriferan body plan towards a different organizational plan through loss of the aquiferous system, a transition that has been hypothesized for the early evolution of Metazoa.Electronic Supplementary Material Supplementary material is available in the online version of this article at 相似文献
8.
Microbial communities of ancient Mediterranean sapropels, buried sediment layers of high organic matter, were analyzed by most probable number (MPN) approaches. Mineral media containing different carbon sources in sub-millimolar concentrations were used. MPN numbers were elevated in sapropels and at the sediment surface, which mirrored total cell count distributions. Highest MPN counts were obtained with a mixture of different monomeric and polymeric substrates, with amino acids or with long-chain fatty acids as sole carbon sources. These values reached up to 2 x 10(7) cm(-3), representing 3.3% of the total cell count. A total of 98 pure cultures were isolated from the highest positive dilutions of the MPN series, representing the most abundant microorganisms culturable by the methods used. The strains were identified by molecular biological methods and could be grouped into 19 different phylotypes. They belonged to the alpha-, beta-, gamma-, and delta-Proteobacteria, to the Actinobacteria and the Firmicutes. However, about half of the number of isolates was closely related to the genera Photobacterium and Agrobacterium. Regarding the high cultivation success, these organisms can be assumed to be typical sapropel bacteria, representing a substantial part of the culturable indigenous microbial community. 相似文献
9.
The depth-related patterns in the benthic megafauna of the NE Weddell Sea shelf at the edge of the Fimbul Ice Shelf were investigated
at seven sites using towed camera platform photographs. Megafaunal density decreased with depth from 77,939 ha−1 at 245 m to 8,895 ha−1 at 510 m. While diversity was variable, with H′ ranging between 1.34 and 2.28, there were no depth related patterns. Multivariate analyses revealed two distinct assemblages;
a shallow assemblage with dense patches of suspension feeders in undisturbed areas and a deep assemblage where these were
not present. Disturbance from icebergs explained many observed patterns in faunal distribution. In shallow waters probable
effects of disturbance were observed as changes in successional stages; in deeper waters changes in habitat as a result of
past disturbance explained faunal distributions. In deeper areas ice ploughing created a mosaic landscape of fine and coarse
sediments. Total megafaunal density was highest in areas of coarse sediment (up to 2.9 higher than in finer sediment areas)
but diversity was highest in intermediate areas (H′ = 2.35). 相似文献
10.
Sumihiro Koyama 《Cytotechnology》2007,55(2-3):125-133
Establishing tissue cultures derived from deep-sea multicellular organisms has been extremely difficult because of the serious
damage they sustain upon decompression and exposure to the high temperature of surface seawater. We developed a novel pressure-stat
aquarium system for the study of living deep-sea multicellular organisms under pressure. Using this system, we have succeeded
in maintaining a variety of deep-sea multicellular organisms under pressure and atmospheric conditions after gradual, slow
decompression. Furthermore, we successfully cultivated and freeze-stocked pectoral fin cells of the deep-sea eel Simenchelys parasiticus collected at a depth of 1,162 m under atmospheric pressure conditions. This review describes novel capture and maintenance
devices for deep-sea organisms and cell culture studies of the organisms under atmospheric and pressure conditions. 相似文献