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21.
Temperature, salinity and abundance of Pyramimonas amyliferawere monitored over a 1-year period in a tidal salt marsh pool.The organism reached two peaks of abundance, the first in latefall before ice covered the pool, and the second in late winterafter the ice had melted. Cysts, but no oc-toflagellate stagesof this organism, were found in the pool in summer. The resultsof growth experiments on a clone of this organism isolated fromthe pool indicate that a temperature between 10 and 15 C isoptimal. A temperature between 20 and 25 C is the maximum tolerableby this clone. The "short-term" salinity tolerance range ofthis clone was found to decrease with increasing temperature,a phenomenon which could affect the fitness of the organismas a tide pool inhabitant. The field and laboratory data indicatethat although temperature and salinity were factors affectingthe abundance of P. amylifera in the pool, other factors notconsidered in the study must have also been important.
*Present address: Department of Biology, University of SouthFlorida, Tampa, Florida, U.S.A. 33620. (Address for reprints) 相似文献
22.
Geoffrey TL Kloppenburg Rick de Graaf Gert ELM Grauls Cathrien A Bruggeman Frank R Stassen 《BMC microbiology》2007,7(1):111
Background
Along with angioplasty, autologus vein grafts are commonly used for artery bypass grafting in patients with advanced arterial stenosis and drug-resistant angina pectoris. Although initially a successful procedure, long-term functionality is limited due to proliferation and migration of smooth muscle cells. Like in atherosclerosis, common chronic infections caused by viruses and bacteria may contribute to this process of vein graft failure. Here we investigated the possible role of Chlamydia pneumoniae (Cpn) in the pathogenesis of venous graft failure in an experimental animal model. In 2 groups (n = 10 rats/group), an epigastric vein-to-common femoral artery interposition graft was placed. Immediately thereafter, rats were infected with Cpn (5*108 IFU) or injected with control solutions. Rats were sacrificed three weeks after surgery and the grafts were harvested for morphometrical and immunohistochemical analysis. 相似文献23.
We isolated and identified strains of marine and freshwater planktonic and benthic microalgae from the vicinity of Indian
River County, Florida (≈27.5°N, 80.34°W), cultivated them in batch culture, and examined their allelopathic activity against
mosquito larvae. Additional algal material was obtained from Syracuse University and the University of Texas—Austin Algal
Culture Collection. Mosquito larvae (Aedes aegypti (L.)) from colonies maintained at the Florida Medical Entomology Laboratory were challenged with the microalgae using log-growth
phase and senescent-phase cultures. Appropriate controls (no algae) were used for each treatment. There were no significant
differences in development time between treatments across all trials and a few significant treatment effects on development
times, mortality, or mosquito size in the individual trials; however, there was a tendency for treatments with senescent microalgae
to develop faster than controls with no algae. Effects consistent with algal toxicity included the two trials with Microcystis aeruginosa, where the larvae exposed to the strain-producing microcystin had significantly longer development times than the controls
or those grown with the non-microcystin-producing strain, and the trial with the dinoflagellate Akashiwo sanguinea, where larvae exposed to this species had significantly higher mortality than the controls. No consistent patterns or differences
between experimental and control treatments in the value of λ′, an estimate of the population finite rate of increase, were discernible from the data. 相似文献
24.
Hudson R. DeYoe Dean A. Stockwell Robert R. Biolagare Mikel Latasa Paul W. Johnson Paul E. Hargraves Curtis A. Suttle 《Journal of phycology》1997,33(6):1042-1048
The Texas brown tide alga (strain TBA-2) is described as Aureoumbra lagunensis Stockwell, DeYoe, Hargraves, et Johnson, gen. et sp. nov. Pigment composition, chloroplast structure, and 18s ribosomal RNA gene sequence data indicate that A. lagunensis and the east coast brown tide alga Aureococcus anophagefferens (originally placed in the Chrysophyceae) belong in the class Pelagophyceae. The new genus Aureoumbra with A. lagunensis as the type species differs from Aureococcus in 18s ribosomal RNA gene sequence, pyrenoid form, nitrogen physiology, and possession of basal bodies. The genus Aureococcus is placed in the order Pelagomonadates and family Pelagomonadaceae while ordinal placement of Aureoumbra is deferred. 相似文献
25.
Background
Tight junctions are an intercellular adhesion complex of epithelial and endothelial cells, and form a paracellular barrier that restricts the diffusion of solutes on the basis of size and charge. Tight junctions are formed by multiprotein complexes containing cytosolic and transmembrane proteins. How these components work together to form functional tight junctions is still not well understood and will require a complete understanding of the molecular composition of the junction. 相似文献26.
The effects of selective ibotenate lesions of the complete hippocampus (CHip), the hippocampal ventral pole (VP), or the medial prefrontal cortex (mPFC) in male rats were assessed on several measures related to energy regulation (i.e., body weight gain, food intake, body adiposity, metabolic activity, general behavioral activity, conditioned appetitive responding). The testing conditions were designed to minimize the nonspecific debilitating effects of these surgeries on intake and body weight. Rats with CHip and VP lesions exhibited significantly greater weight gain and food intake compared with controls. Furthermore, CHip-lesioned rats, but not rats with VP lesions, showed elevated metabolic activity, general activity in the dark phase of the light-dark cycle, and greater conditioned appetitive behavior, compared with control rats without these brain lesions. In contrast, rats with mPFC lesions were not different from controls on any of these measures. These results indicate that hippocampal damage interferes with energy and body weight regulation, perhaps by disrupting higher-order learning and memory processes that contribute to the control of appetitive and consummatory behavior. 相似文献
27.
The geographic apportionment of mitochondrial genetic diversity in east African chimpanzees, Pan troglodytes schweinfurthii 总被引:3,自引:1,他引:2
This study is a geographically systematic genetic survey of the easternmost
subspecies of chimpanzee, Pan troglodytes schweinfurthii. DNA was
noninvasively collected in the form of shed hair from chimpanzees of known
origin in Uganda, Rwanda, Tanzania, and Zaire. Two hundred sixty-two DNA
sequences from hypervariable region 1 of which of the mitochondrial control
region were generated. Eastern chimpanzees display levels of mitochondrial
genetic variation which are low and which are similar to levels observed in
humans (Homo sapiens). Also like humans, between 80% and 90% of the genetic
variability within the eastern chimpanzees is apportioned within
populations. Spatial autocorrelation analysis shows that genetic similarity
between eastern chimpanzees decreases clinically with distance, in a
pattern remarkably similar to one seen for humans separated by equivalent
geographic distances. Eastern chimpanzee mismatch distributions (frequency
distributions of pairwise genetic differences between individuals) are
similar in shape to those for humans, implying similar population histories
of recent demographic expansion. The overall pattern of genetic variability
in eastern chimpanzees is consistent with the hypothesis that the subject
has responded demographically to paleoclimatically driven changes in the
distribution of eastern African forests during the recent Pleistocene.
相似文献
28.
A nitrogen limitation technique elicited the entire life cycle of the marine centric diatoms Chaetoceros diadema (Ehr.) Gran and Leptocylindrus danicus Cleve. In C. diadema the sexual cycle followed the same pattern as in the previously investigated C. didymus. Sexuality took place in narrow diameter cells, only at 2 and 5° C, and was seldom seen. Resting spore formation took place in cells of all sizes and at all temperatures at which the species grew vegetatively (2–15° C). The L. danicus life cycle is probably unique among diatoms. Nitrogen depletion induced sexuality in the entire culture at 10 and 15° C if the cell diameter was narrow (3–8 μm). Auxospore formation was followed by resting spore formation directly within the auxospore. In C. diadema, as in most centric diatoms, resting spores are not an obligate part of the life cycle, but they are in L. danicus. Resting spore formation is a versatile adaptive response in C. diadema, depending only on nitrogen depletion, although promoted by low temperatures. In L. danicus the linkage to the sexual process sharply limits conditions under which resting spores can form. 相似文献
29.
Paul E. Hargraves 《Journal of phycology》1976,12(3):285-291
The structure of the tropical oceanic diatom Gossleriella tropica Schütt was examined in the light and electron microscopes. The species is characterized by a primarily poroid valve, surface, it single central labiate process and a unique ring of spines attached to the cingulum. Placement of the genus in the family Rhizosoleniaceae is suggested. Although G. tropica is widely distributed in the world's oceans, it is usually confined to the lower photic zone, salinities of 34.5–35.5% and temperatures of 15–30 C. 相似文献
30.
Cyclic 3', 5'-AMP relay dictyostelium discoideum. V. Adaptation of the cAMP signaling response during cAMP stimulation
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In dictyostelium discoideum, extracellular cAMP activates adenylate cyclase, which leads to an increase in intracellular cAMP and the rate of cAMP secretion. The signaling response to a constant cAMP stimulus is terminated after several minutes by an adaptation mechanism. The time- course of adaptation stimuli of 10(-6) or 10(-7) M cAMP was assessed. We used a perfusion technique to deliver defined cAMP stimuli to [(3)H]adenosine-labeled amoebae and monitored their secretion of [(3)H]cAMP. Amoebae were pretreated with 10(-6) or 10(-7) M cAMP to periods of 0.33-12 minutes, and then immediately given test stimuli of 10(-8) M to 2.5 x 10(-7) M cAMP. The response to a given test stimulus was progressively attenuated and finally extinguished as the duration of the pretreatment stimulus increased. During concentration of the test stimulus. The responses to test stimuli of 10(-8), 5 x 10(-8), 10(-7), or 2.5 x 10(-7) M cAMP were extinguished after approximately 1, 2.25,2.5, and 10 min, respectively. 1.5 min of stimulation with 10(-7) M cAMP was necessary to extinguish the response of a test stimulus of 10(-8) M cAMP. Our data suggest that adaptation begins within 20 s of stimulation, rises rapidly for approximately 2.5 min, and reaches a plateau after approximately 10 min. The absolute rate of rise was faster during pretreatment with 10(-6) than with 10(-7) M cAMP. These results support a working hypothesis in which the occupancy of surface cAMP receptors leads to changes in two opposing cellular processes, excitation and adaptation, that control the activity of D. discoideum adenylate cyclase. 相似文献