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81.
Recently, a group of diplomonads has been found to use a genetic code in
which TAA and TAG encode glutamine rather than termination. To survey the
distribution of this characteristic in diplomonads, we sought to identify
TAA and TAG codons at positions where glutamine is expected in genes for
alpha-tubulin, elongation factor-1 alpha, and the gamma subunit of
eukaryotic translation initiation factor-2. These sequences show that the
variant genetic code is utilized by almost all diplomonads, with the genus
Giardia alone using the universal genetic code. Comparative phylogenetic
analysis reveals that the switch to this genetic code took place very early
in the evolution of diplomonads and was likely a single event. Termination
signals and downstream untranslated regions were also cloned from three
Hexamita genes. In all three of these genes, the predicted TGA termination
codon was found at the expected position. Interestingly, the untranslated
regions of these genes are high in AT. This is incongruent with the coding
regions, which are comparatively GC-rich.
相似文献
82.
The growth of the hyperthermophilic, anaerobic bacterium Thermotoga neapolitana is stimulated by elemental sulfur by an unknown mechanism. We detected hydrogen-dependent sulfur reductase (sulfhydrogenase) and polysulfide dehydrogenase activities in cell extracts of this organism, demonstrating that it has at least two pathways for sulfidogenesis. Hydrogen-dependent sulfur reductase and hydrogenase activities are catalyzed by the purified hydrogenase of Thermotoga maritima, and this enzyme was called the sulfhydrogenase (K. Ma, R. N. Schicho, R. M. Kelly, and M. W. W. Adams, Proc. Natl. Acad. Sci. USA 90:5341-5344, 1993). Cells grown without elemental sulfur or cystine had 1.3 to 3.3 times higher sulfhydrogenase activities than those grown with either of these sources of sulfane sulfur. Hydrogenase activity was 2 to 5 times higher. Polysulfide dehydrogenase was up to 48-fold more active in cell extracts than the sulfhydrogenase. The activity of polysulfide dehydrogenase was approximately twofold higher when cells were grown in the presence of elemental sulfur. Its activity was oxygen labile in crude extracts, and it appears to be a cytoplasmic enzyme. Polysulfide was preferred over elemental sulfur as an electron acceptor (Km = 0.15 mM) and was more active with NADH (Km = 0.03 mM) than NADPH (Km = 0.41 mM). Growth in the presence of elemental sulfur appeared to slightly increase the activity of polysulfide dehydrogenase and slightly decrease both activities of sulfhydrogenase (hydrogenase and polysulfide reductase), while growth without elemental sulfur had the opposite effects. The greater activity of polysulfide dehydrogenase and its apparent regulation indicate that it is the more physiologically important means of polysulfide reduction. 相似文献
83.
Emerging From the Unknown: Structural and Functional Features of Agnoprotein of Polyomaviruses
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84.
Daniel L. Childers 《Hydrobiologia》2006,569(1):531-544
This paper synthesizes research conducted dusring the first 5–6 years of the Florida Coastal Everglades Long-Term Ecological
Research Program (FCE LTER). My objectives are to review our research to date, and to present a new central theme and conceptual
approach for future research. Our research has focused on understanding how dissolved organic matter (DOM) from upstream oligotrophic
marshes interacted with a marine source of the limiting nutrient, phosphorus (P), to control productivity in the oligohaline
estuarine ecotone. We have been working along freshwater to marine transects in two drainage basins located in Everglades
National Park (ENP). The Shark River Slough transect (SRS) has a direct connection to the Gulf of Mexico, providing this estuarine
ecotone with a source of marine P. The oligohaline ecotone along our southern Everglades transect (TS/Ph), however, is separated
from this marine P source by the Florida Bay estuary. We originally hypothesized an ecosystem productivity peak in the SRS
ecotone, driven by the interaction of marine P and Everglades DOM, but no such productivity peak in the TS/Ph ecotone because
of this lack of marine P. Our research to date has tended to show the opposite pattern, however, with many ecosystem components
showing enhanced productivity in the TS/Ph ecotone, but not in the SRS ecotone. Water column P concentrations followed a similar
pattern, with unexpectedly high P in the TS/Ph ecotone during the dry season. Our organic geochemical research has shown that
Everglades DOM is more refractory than originally hypothesized. We have also begun to understand the importance of detrital
organic matter production and transport to ecotone dynamics and as the base of aquatic food webs. Our future research will
build on this substantial body of knowledge about these oligotrophic estuaries. We will direct our efforts more strongly on
biophysical dynamics in the oligohaline ecotone regions. Specifically, we will be focusing on inputs to these regions from
four primary water sources: freshwater Everglades runoff, net precipitation, marine inputs, and groundwater. We are hypothesizing
that dry season groundwater inputs of P will be particularly important to TS/Ph ecotone dynamics because of longer water residence
times in this area. Our organic geochemical, biogeochemical, and ecosystem energetics work will focus more strongly on the
importance of detrital organics and will take advantage of a key Everglades Restoration project, scheduled for 2008 or 2009,
that will increase freshwater inputs to our SRS transect only. Finally, we will also begin to investigate the human dimensions
of restoration, and of a growing population in south Florida that will become increasingly dependent on the Everglades for
critical ecosystem services (including fresh water) even as its growth presents challenges to Everglades sustainability. 相似文献
85.
The contribution of leaching to the rapid release of nutrients and carbon in the early decay of wetland vegetation 总被引:2,自引:1,他引:1
Our goal was to quantify the coupled process of litter turnover and leaching as a source of nutrients and fixed carbon in
oligotrophic, nutrient-limited wetlands. We conducted poisoned and non-poisoned incubations of leaf material from four different
perennial wetland plants (Eleocharis spp., Cladium jamaicense, Rhizophora mangle and Spartina alterniflora) collected from different oligotrophic freshwater and estuarine wetland settings. Total phosphorus (TP) release from the
P-limited Everglades plant species (Eleocharis spp., C. jamaicense and R. mangle) was much lower than TP release by the salt marsh plant S. alterniflora from N-limited North Inlet (SC). For most species and sampling times, total organic carbon (TOC) and TP leaching losses were
much greater in poisoned than non-poisoned treatments, likely as a result of epiphytic microbial activity. Therefore, a substantial
portion of the C and P leached from these wetland plant species was bio-available to microbial communities. Even the microbes
associated with S. alterniflora from N-limited North Inlet showed indications of P-limitation early in the leaching process, as P was removed from the water
column. Leaves of R. mangle released much more TOC per gram of litter than the other species, likely contributing to the greater waterborne [DOC] observed
by others in the mangrove ecotone of Everglades National Park. Between the two freshwater Everglades plants, C. jamaicense leached nearly twice as much P than Eleocharis spp. In scaling this to the landscape level, our observed leaching losses combined with higher litter production of C. jamaicense compared to Eleocharis spp. resulted in a substantially greater P leaching from plant litter to the water column and epiphytic microbes. In conclusion,
leaching of fresh plant litter can be an important autochthonous source of nutrients in freshwater and estuarine wetland ecosystems. 相似文献
86.
Jeroen CW Rijk Ad ACM Peijnenburg Peter JM Hendriksen Johan M Van Hende Maria J Groot Michel WF Nielen 《BMC veterinary research》2010,6(1):44
Background
Within the European Union the use of growth promoting agents in animal production is prohibited. Illegal use of natural prohormones like dehydroepiandrosterone (DHEA) is hard to prove since prohormones are strongly metabolized in vivo. In the present study, we investigated the feasibility of a novel effect-based approach for monitoring abuse of DHEA. Changes in gene expression profiles were studied in livers of bull calves treated orally (PO) or intramuscularly (IM) with 1000 mg DHEA versus two control groups, using bovine 44K DNA microarrays. In contrast to controlled genomics studies, this work involved bovines purchased at the local market on three different occasions with ages ranging from 6 to 14 months, thereby reflecting the real life inter-animal variability due to differences in age, individual physiology, season and diet. 相似文献87.
Seven citrus orchards on reduced- to no-pesticide spray programs were sampled for predacious mites in the family Phytoseiidae
(Acari: Mesostigmata) in central and south central Florida. Inner and outer canopy leaves, open flowers, fruit, twigs, and
trunk scrapings were sampled monthly between September 1994 and January 1996. Vines and ground cover plants were sampled monthly
between September 1994 and January 1996 in five of these orchards. The two remaining orchards were on full herbicide programs
and ground cover plants were absent. Thirty-three species of phytoseiid mites were identified from 35,405 specimens collected
within citrus tree canopies within the seven citrus orchards, and 8,779 specimens from vines and ground cover plants within
five of the seven orchards. The six most abundant phytoseiid species found within citrus tree canopies were: Euseius mesembrinus (Dean) (20,948), Typhlodromalus peregrinus (Muma) (8,628), Iphiseiodes quadripilis (Banks) (2,632), Typhlodromips dentilis (De Leon) (592), Typhlodromina subtropica Muma and Denmark (519), and Galendromus helveolus (Chant) (315). The six most abundant species found on vines or ground cover plants were: T. peregrinus (6,608), E. mesembrinus (788), T. dentilis (451), I. quadripilis (203), T. subtropica (90), and Proprioseiopsis asetus (Chant) (48). The remaining phytoseiids included: Amblyseius aerialis (Muma), A. herbicolus (Chant), A. largoensis (Chant), A. multidentatus (Chant), A. sp. near multidentatus, A. obtusus (Koch), Chelaseius vicinus (Muma), Euseius hibisci Chant, Galendromus gratus (Chant), Metaseiulus mcgregori (Chant), Neoseiulus mumai (Denmark), N. vagus (Denmark), Phytoscutus sexpilis (Muma), Phytoseiulus macropilis (Banks), Proprioseiopsis detritus (Muma), P. dorsatus (Muma), P. macrosetae (Banks), P. rotundus (Muma), P. solens (De Leon), Typhlodromips deleoni (Muma), T. dillus (De Leon), T. dimidiatus (De Leon), T. mastus Denmark and Muma, T. simplicissimus (De Leon), and T. sp. near tunus, and Typhlodromus transvaalensis (Nesbitt). Eighty-two ground cover plants or vines were sampled within the five orchards and one or more phytoseiids were collected
from 71 of these plants. Five ground cover plants with the highest numbers of phytoseiids included: Bidens alba (L.) DC (1,420 mites within 13 species), Solanum americanum L. (1,355 mites within 8 species), Amaranthus spinosus L. (1,137 mites within 11 species), Gnaphalium pensylvanicum Willd. (844 mites within 8 species) and Richardia brasiliensis (Meg.) Gomez (354 mites within 8 species). 相似文献
88.
The discovery that all hyperthermophiles that have been evaluated have the capacity to reduce Fe(III) has raised the question of whether mechanisms for dissimilatory Fe(III) reduction have been conserved throughout microbial evolution. Many studies have suggested that c-type cytochromes are integral components in electron transport to Fe(III) in mesophilic dissimilatory Fe(III)-reducing microorganisms. However, Pyrobaculum islandicum, the hyperthermophile in which Fe(III) reduction has been most intensively studied, did not contain c-type cytochromes. NADPH was a better electron donor for the Fe(III) reductase activity in P. islandicum than NADH. This is the opposite of what has been observed with mesophiles. Thus, if previous models for dissimilatory Fe(III) reduction by mesophilic bacteria are correct, then it is unlikely that a single strategy for electron transport to Fe(III) is present in all dissimilatory Fe(III)-reducing microorganisms. 相似文献
89.
Cyclists with unilateral transtibial amputation (CTA) provide a unique model to study integration of the neuromuscular and bicycle systems while having the option to modify this integration via the properties of the prosthesis. This study included eight CTA and nine intact cyclists. The cyclists pedaled on a stationary bicycle with instrumented force pedals. The CTA group pedaled with a stiff or flexible prosthetic foot during a simulated time trial and a low difficulty condition. During the time trial condition, pedaling with the flexible foot resulted in force and work asymmetries of 11.4% and 30.5%, the stiff foot displayed 11.1% and 21.7%, and the intact group displayed 4.3% and 4.2%, respectively. Similar trends were shown in the low difficulty condition. These data suggest foot stiffness has an effect on cycling symmetry in amputees. 相似文献
90.
The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland
ecosystems, and contribute to landscape-scale heterogeneity. Tree islands are important ecosystems because they increase ecological
heterogeneity in the Everglades landscape and in many tropical landscapes. Only slight differences in elevation due to peat
accumulation allow the differentiation of these systems from the adjacent marsh. Hydrologic restoration of the Everglades
landscape is currently underway, and increased nutrient supply that could occur with reintroduction of freshwater flow may
alter these differentiation processes. In this study, we established a landscape-scale, ecosystem-level experiment to examine
litter decomposition responses to increased freshwater flow in nine tree islands and adjacent marsh sites in the southern
Everglades. We utilized a standard litterbag technique to quantify changes in mass loss, decay rates, and phosphorus (P),
nitrogen (N) and carbon (C) dynamics of a common litter type, cocoplum (Chrysobalanus icaco L.) leaf litter over 64 weeks. Average C. icaco leaf degradation rates in tree islands were among the lowest reported for wetland ecosystems (0.23 ± 0.03 yr−1). We found lower mass loss and decay rates but higher absolute mass C, N, and P in tree islands as compared to marsh ecosystems
after 64 weeks. With increased freshwater flow, we found generally greater mass loss and significantly higher P concentrations
in decomposing leaf litter of tree island and marsh sites. Overall, litter accumulated N and P when decomposing in tree islands,
and released P when decomposing in the marsh. However, under conditions of increased freshwater flow, tree islands accumulated
more P while the marsh accumulated P rather than mineralizing P. In tree islands, water level explained significant variation
in P concentration and N:P molar ratio in leaf tissue. Absolute P mass increased strongly with total P load in tree islands
(r
2 = 0.81). In the marsh, we found strong, positive relationships with flow rate. Simultaneous C and P accumulation in tree
island and mineralization in adjacent marsh ecosystems via leaf litter decomposition promotes landscape differentiation in
this oligotrophic Everglades wetland. However, results of this study suggest that variation in flow rates, water levels and
TP loads can shift differential P accumulation and loss leading to unidirectional processes among heterogeneous wetland ecosystems.
Under sustained high P loading that could occur with increased freshwater flow, tree islands may shift to litter mineralization,
further degrading landscape heterogeneity in this system, and signaling an altered ecosystem state. 相似文献