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Methanogens growing on C-1 substrates synthesize 2-carbon acetyl groups in the form of acetyl-CoA for carbon assimilation
using the multienzyme complex acetyl-CoA decarbonylase/synthase (ACDS) which contains five different subunits encoded within
an operon. In species growing on acetate ACDS also functions to cleave the acetate C-C bond for energy production by methanogenesis.
A number of species of Methanosarcina that are capable of growth on either C-1 compounds or acetate contain two separate ACDS operons, and questions have been
raised about whether or not these operons play separate roles in acetate synthesis and cleavage. Methanosarcina thermophila genomic DNA was analyzed for the presence of two ACDS operons by PCR amplifications with different primer pairs, restriction
enzyme analyses, DNA sequencing and Southern blot analyses. A single ACDS operon was identified and characterized, with no
evidence for more than one. MALDI mass spectrometric analyses were carried out on ACDS preparations from methanol- and acetate-grown
cells. Peptide fragmentation patterns showed that the same ACDS subunits were present regardless of growth conditions. The
evidence indicates that a single form of ACDS is used both for acetate cleavage during growth on acetate and for acetate synthesis
during growth on C-1 substrates.
Electronic Supplementary Material Supplementary material is available for this article at
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David A. Grahame (Corresponding author)Email: |
Edward DeMoll (Corresponding author)Email: |
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Sub-Antarctic Marion Island has had a permanent research station for 50 years and the islands Wandering Albatrosses have been intensively studied for 20 years. The reactions of breeding birds to approaches by a human on foot were recorded. Three response variables were calculated: intensity of vocal reaction (IVR), intensity of non-vocal reaction (INR) and overall response index (ORI). At 5 m from the nest, twice as many birds stood and/or vocalised as at 15 m. Nearest neighbour distance, age and gender did not explain individual variability of responses. Study colony birds had higher IVR scores than non-study colony birds; birds at colonies closest to the station had the highest ORI scores. A better breeding record was associated with lower IVR and ORI scores, but a causative relationship remains to be demonstrated. A minimum viewing distance of 25 m is recommended for breeding Wandering Albatrosses.
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Marienne S. de VilliersEmail: Fax: +27-21-6503434 |
John CooperEmail: |
Peter G. RyanEmail: |
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Machado RR Lima Filho ES Jardim DF Ferreira MA de Faria CG Duarte RS Lesche B 《European biophysics journal : EBJ》2008,38(1):111-119
An interferometer that measures the refractive index changes due to bacterial metabolism is described. The apparatus permits
simultaneous and real time measurement of bacterial growth in several samples of slowly growing mycobacteria. The error sources
are discussed and the sensitivity of the apparatus is tested. For the species Mycobacterium bovis BCG and M. smegmatis, a relation between refractive index change and bacterial concentration is determined experimentally and the time constant
of bacterial growth is measured.
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B. LescheEmail: |
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The recent contribution by Jarmila Kukalová-Peck on Hennigian phylogenetics and hexapod limb evolution is critically evaluated.
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Michael S. Engel (Corresponding author)Email: |
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A key point in the analysis of dynamical models of biological systems is to handle systems of relatively high dimensions.
In the present paper we propose a method to hierarchically organize a certain type of piecewise affine (PWA) differential
systems. This specific class of systems has been extensively studied for the past few years, as it provides a good framework
to model gene regulatory networks. The method, shown on several examples, allows a qualitative analysis of the asymptotic
behavior of a PWA system, decomposing it into several smaller subsystems. This technique, based on the well-known strongly
connected components decomposition, is not new. However, its adaptation to the non-smooth PWA differential equations turns
out to be quite relevant because of the strong discrete structure underlying these equations. Its biological relevance is
shown on a 7-dimensional PWA system modeling the gene network responsible for the carbon starvation response in Escherichia coli.
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Laurent Tournier (Corresponding author)Email: |
Jean-Luc GouzéEmail: |
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This paper introduces a threshold policy with hysteresis (TPH) for the control of one-predator one-prey models. The models studied are the Lotka–Volterra and Rosenzweig–MacArthur
two species density-dependent predator–prey models and the Arditi–Ginzburg nondimensional ratio-dependent model. The proposed
policy (TPH) changes the dynamics of the system in such a way that a bounded oscillation is achieved confined to a region
that does not allow extinction of either species. The policy can be designed by a suitable choice of so called virtual equilibrium
points in a simple and intuitive manner.
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Amit Bhaya (Corresponding author)Email: |
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Jason E. E. Dampier Nancy Luckai F. Wayne Bell William D. Towill 《Biodiversity and Conservation》2007,16(10):2933-2948
Concern about forestry practices creating tree-level monoculture plantations exists. Our study investigates tree diversity
responses for six early seral boreal forest plantations in Ontario, Canada, representing three conifer species; black spruce
(Picea mariana), white spruce (P. glauca), and jack pine (Pinus banksiana), 14 release treatments, and 94 experimental units. Dominance-diversity curves and Simpson’s indices of diversity and evenness
indicate tree alpha diversity. We propose a new method for assessing diversity, using percentage of theoretical species maximum
(%TSM) which is determined by comparing post-disturbance richness (S) with a theoretical species maximum (TSM). Our results support the hypothesis that alternative vegetation release treatments
generally do not reduce tree species diversity levels (%TSM) relative to untreated plots. The only %TSM (P ≤ 0.05) comparison that produced less diversity than in control plots was repeated annual treatments of Vision herbicide
at one of the black spruce study sites. Our results generally support the hypothesis that tree monocultures do not develop
after vegetation release. Only one out of 94 experimental units developed into a tree layer monoculture (Simpson’s reciprocal
diversity index = 1). Again this was one of the repeated annual treatments of Vision herbicide at one of the black spruce
study sites—a treatment which is atypical of Canadian forest management.
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Jason E. E. DampierEmail: |
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Summary The tree species Berlinia korupensis Mackinder & Burgt is described as new. The species is endemic to the southern part of
Korup National Park in Cameroon. Seventeen trees have been found so far, the largest being 42 m high and having a trunk diam.
of 88 cm. The new species is assessed as Critically Endangered (CR D) under the criteria of IUCN. Two distribution maps are
included; one map indicating the single locality in Cameroon near the Nigerian border where the new species was found and
another map of the permanent plot where 14 of the 17 trees were recorded. A line drawing is also included, along with colour
photographs of the flowers and the trunk.
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Barbara A. MackinderEmail: |
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Alison M. Strange Geoffrey H. Griffiths Sophie Hine Kim Young Graham J. Holloway 《Journal of Insect Conservation》2007,11(3):241-249
The Small Red Damselfly (Ceriagrion tenellum) (De Villiers) (Odonata: Coenagrionidae: Ceriagrion) is classed as vulnerable (Shirt, British Red Data Book, Nature Conservancy Council, Peterborough, UK, 1987) throughout the
UK, and is included in certain Local Biodiversity Action Plans (LBAPs) in the south. A large proportion of any Biodiversity
Action Plan is concerned with the requirement of conservation and management programmes. In order to guide them, information
about the habitat preferences of the species concerned is vital. Detailed habitat information was collected to include a variety
of physical parameters particularly vegetation, both in-channel and bankside. The species was found to be primarily associated
with in-channel emergent broad-leaved plants, bankside grasses and rushes, and shallow, narrow channels with dark organic
substrate. The consequences of these findings are discussed in relation to the conservation and management of C. tenellum.
相似文献
Alison M. StrangeEmail: |
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Lévy Flights in Dobe Ju/’hoansi Foraging Patterns 总被引:1,自引:0,他引:1
Clifford T. Brown Larry S. Liebovitch Rachel Glendon 《Human ecology: an interdisciplinary journal》2007,35(1):129-138
We analyzed data on Ju/’hoansi hunter–gatherer foraging patterns and found that their movements between residence camps can
be modeled as a Lévy flight. The step lengths of their movements scale as a power law with an exponent μ = 1.97. Their wait times (residence times) at the camps also scale as a power law (μ = 1.45). A Lévy flight with step lengths μ = 2 is an optimal search pattern for scarce, randomly located targets; thus, the Ju/’hoansi foraging pattern may approach
an optimal search in this area of sparse plant and animal resources. These findings affect the application of optimal foraging
theory to humans in anthropology and archaeology because they alter the way in which search and travel times should be quantified.
These results may also carry implications for the study of other patterns of human movement, such as demic diffusion and migration.
相似文献
Clifford T. BrownEmail: |
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Lance S. Evans Zella Kahn-Jetter Jessica Torres Mabel Martinez Paul Tarsia 《Trees - Structure and Function》2008,22(3):283-289
Land plants have evolved a large number of growth forms and each plant species has a unique morphology. For many tall plants,
main stems serve the function of vertical growth while primary and higher order branches are responsible for lateral growth
for greater light interception. Herein we search for a mechanical constant for primary branches. Primary branches were sampled
from 40 species of trees and shrubs. Among the species sampled, branch lengths ranged from 1.8 to 12.2 m, weights from 0.056
to 16.6 kg, base diameters from 17 to 150 mm, bending moments from 7.1 to 2,200 N-m, and section moduli from 0.039 to 29.0 × 10−3 m3. Primary branches of all 40 tree and shrub species exhibited relatively constant bending stresses along each branch. Moreover
stress values among the 40 species were relatively constant at about 11 MPa (mean = 11.1 MPa [range 5.2–18.9]; standard deviation = 3.3 MPa).
Furthermore, primary branches without secondary branches attached (1) had similar bending moment distributions as tapered
cantilever beams, (2) exhibited relatively constant slope values of stress versus length among all species (stresses increased
linearly with length), and (3) exhibited both relatively constant density and relatively constant taper within each species.
We conclude that the relatively constant stress of about 11 MPa of primary branches was due solely to the numbers, weights,
and distributions of secondary branches and associated higher order branches along primary branches for the 40 plant species.
To our knowledge, this is the first publication that shows a unifying mechanical constant for primary branches of plants.
相似文献
Lance S. EvansEmail: |
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To our knowledge, this paper is the first record/report of a juvenile light-coloured Weddell seal (Leptonychotes weddellii) at Cape Shirreff, Livingston Island in January 1998, determining that it was an albino individual. Based on available literature,
three cases of albino seals have been reported exclusively for Harbour seal pups, and no albino has been reported for Antarctic
pagophilic true seals. Therefore, this is the first confirmed case of albinism in Antarctic pagophilic true seals species,
indicating that this phenomenon is indeed of a rare occurrence.
相似文献
Daniel TorresEmail: |
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Populations of ten Amazonian bird species were sampled on opposite banks of the Rio Teles Pires, a headwater stream of the Rio Tapajós, in the Alta Floresta region, northern Mato Grosso, Brazil. The river is 100–300 m wide in this region. We found a range of genetic differentiation from none to relatively high levels; six of the ten species studied exhibit what appear to be genetic breaks at the river. With one exception, the antbird Hylophylax poecilinota, there is no morphologically recognized differentiation correlating with genetic differentiation. From the perspective of traditional morphology-based taxonomy, the Rio Teles Pires is not a faunal barrier. Rather, contact zones between members of species and subspecies pairs appear more or less randomly distributed in this region, some being located at varying distances to the east, others at varying distances to the west of the Rio Teles Pires, with few following the course of this river itself.
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Jürgen HafferEmail: Phone: +49-201-710426 |
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The presence of several types of allelochemicals has been reported from Ajuga, a Labiatae genus comprising more than 40 species of wide distribution in extratropical regions of both hemispheres. The
genus is of great medicinal and economic importance and among the biological properties of the secondary metabolites, the
antifeedant activity against pest insects appears to be related to the presence of neo-clerodane type diterpenes. This review focuses on the isolation and structural elucidation of this type of compounds from
Ajuga species and the hemisynthetic compounds of closely related structure obtained. The reported biological activity of crude
extracts and isolated diterpenes will be briefly commented.
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Josep CollEmail: |