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991.
The distribution of bacterial and archaeal species in Crater Lake plankton varies dramatically over depth and with time, as
assessed by hybridization of group-specific oligonucleotides to RNA extracted from lakewater. Nonmetric, multidimensional
scaling (MDS) analysis of relative bacterial phylotype densities revealed complex relationships among assemblages sampled
from depth profiles in July, August and September of 1997 through 1999. CL500-11 green nonsulfur bacteria (Phylum Chloroflexi)
and marine Group I crenarchaeota are consistently dominant groups in the oxygenated deep waters at 300 and 500 m. Other phylotypes
found in the deep waters are similar to surface and mid-depth populations and vary with time. Euphotic zone assemblages are
dominated either by β-proteobacteria or CL120-10 verrucomicrobia, and ACK4 actinomycetes. MDS analyses of euphotic zone populations
in relation to environmental variables and phytoplankton and zooplankton population structures reveal apparent links between
Daphnia pulicaria zooplankton population densities and microbial community structure. These patterns may reflect food web interactions that
link kokanee salmon population densities to community structure of the bacterioplankton, via fish predation on Daphnia with cascading consequences to Daphnia bacterivory and predation on bacterivorous protists. These results demonstrate a stable bottom-water microbial community.
They also extend previous observations of food web-driven changes in euphotic zone bacterioplankton community structure to
an oligotrophic setting. 相似文献
992.
993.
Applications of whole-cell bacterial sensors in biotechnology and environmental science 总被引:2,自引:0,他引:2
Yagi K 《Applied microbiology and biotechnology》2007,73(6):1251-1258
Biosensors have major advantages over chemical or physical analyses with regard to specificity, sensitivity, and portability.
Recently, many types of whole-cell bacterial biosensors have been developed using recombinant DNA technology. The bacteria
are genetically engineered to respond to the presence of chemicals or physiological stresses by synthesizing a reporter protein,
such as luciferase, β-galactosidase, or green fluorescent protein. In addition to an overview of conventional biosensors,
this minireview discusses a novel type of biosensor using a photosynthetic bacterium as the sensor strain and the crtA gene, which is responsible for carotenoid synthesis, as the reporter. Since bacteria possess a wide variety of stress-response
mechanisms, including antioxidation, heat-shock responses, nutrient-starvation, and membrane-damage responses, DNA response
elements for several stress-response proteins can be fused with various reporter genes to construct a versatile set of bacterial
biosensors for a variety of analytes. Portable biosensors for on-site monitoring have been developed using a freeze-dried
biosensing strain, and cell array biosensors have been designed for high-throughput analysis. Moreover, in the future, the
use of single-cell biosensors will permit detailed analyses of samples. Signals from such sensors could be detected with digital
imaging, epifluorescence microscopy, and/or flow cytometry. 相似文献
994.
Meissner D Vollstedt A van Dijl JM Freudl R 《Applied microbiology and biotechnology》2007,76(3):633-642
In contrast to the general protein secretion (Sec) system, the twin-arginine translocation (Tat) export pathway allows the
translocation of proteins across the bacterial plasma membrane in a fully folded conformation. Due to this feature, the Tat
pathway provides an attractive alternative to the secretory production of heterologous proteins via the Sec system. In this
study, the potential for Tat-dependent heterologous protein secretion was compared in the three Gram-positive bacteria Staphylococcus carnosus, Bacillus subtilis, and Corynebacterium glutamicum using green fluorescent protein (GFP) as a model protein. In all three microorganisms, fusion of a Tat signal peptide to
GFP resulted in its Tat-dependent translocation across the corresponding cytoplasmic membranes. However, striking differences
with respect to the final localization and folding status of the exported GFP were observed. In S. carnosus, GFP was trapped entirely in the cell wall and not released into the supernatant. In B. subtilis, GFP was secreted into the supernatant, however, in an inactive form. In contrast, C. glutamicum effectively secreted active GFP. Our results clearly demonstrate that a comparative evaluation of different Gram-positive
host microorganisms is a crucial step on the way to an efficient Tat-mediated secretory production process for a desired heterologous
target protein.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This paper is dedicated to Hermann Sahm on the occasion of his 65th birthday. 相似文献
995.
Bussiek M Müller G Waldeck W Diekmann S Langowski J 《European biophysics journal : EBJ》2007,37(1):81-93
Alpha-satellite DNA (AS) is part of centromeric DNA and could be relevant for centromeric chromatin structure: its repetitive
character may generate a specifically ordered nucleosomal arrangement and thereby facilitate kinetochore protein binding and
chromatin condensation. Although nucleosomal positioning on some satellite sequences had been shown, including AS from African
green monkey (AGM), the sequence-dependent nucleosomal organisation of repetitive AS of this species has so far not been analysed.
We therefore studied the positioning of reconstituted nucleosomes on AGM AS tandemly repeated DNA. Enzymatic analysis of nucleosome
arrays formed on an AS heptamer as well as the localisation of mononucleosomes on an AS dimer by atomic force microscopy (AFM)
showed one major positioning frame, in agreement with earlier results. The occupancy of this site was in the range of 45–50%,
in quite good agreement with published in vivo observations. AFM measurements of internucleosomal distances formed on the
heptamer indicated that the nucleosomal arrangement is governed by sequence-specific DNA-histone interactions yielding defined
internucleosomal distances, which, nevertheless, are not compatible with a uniform phasing of the nucleosomes with the AGM
AS repeats. 相似文献
996.
The primary objective of this study was to determine the reproductive structure of the adult green sturgeon population in
the Rogue River. Green sturgeon were captured by gillnet in the lower 11.6–68.4 river kilometers in April to July 2000–2003
and September and October 2002–2003. Gonadal tissue, collected by biopsy, was processed histologically, blood was collected
from the caudal vasculature, and fork length (FL) and total length (TL) (±0.5 cm) were measured for each individual. Sex steroids,
testosterone (T), 11-ketotestosterone (11-KT), and estradiol-17β (E2), were measured by radioimmunoassay. Biological samples
were collected from a total of 88 green sturgeon of which 37 females and 41 males were confirmed by histological analysis.
Four gravid females, captured in the spring, were visually identified, and oocyte polarization index and ovarian follicle
diameter indicated that these females were in spawning condition. Gonadal samples collected from six individuals did not contain
gonial cells, hence the sex and stage of maturity in these individuals remains unknown. Of the 20 females captured in the
spring, 1 was vitellogenic, 4 were post-vitellogenic, and 15 were post-ovulatory. Twenty-one females were captured in the
fall of which 6 were pre-vitellogenic, 7 vitellogenic, and 8 post-ovulatory. Of the 16 males captured in the spring, 2 were
pre-meiotic, 8 were ripe or actively spermiating, and 6 were post-spermiation. Twenty-five males were captured in the fall:
11 pre-meiotic males and 14 post-spermiation. The majority of green sturgeon captured in the Rogue River were reproductively
active or had recently spawned indicating the importance of this river for the preservation of green sturgeon. 相似文献
997.
Protective effects of EGCg or GCg, a green tea catechin epimer, against postischemic myocardial dysfunction in guinea-pig hearts 总被引:1,自引:0,他引:1
Hirai M Hotta Y Ishikawa N Wakida Y Fukuzawa Y Isobe F Nakano A Chiba T Kawamura N 《Life sciences》2007,80(11):1020-1032
The protective effects of (-)-epigallocatechin-3-gallate (EGCg) or the C-2 epimer, (-)-gallocatechin-3-gallate (GCg), afforded by their antioxidative activity among green tea catechins were investigated in perfused guinea-pig Langendorff hearts subjected to ischemia and reperfusion. The recovery (%) of the left ventricular developed pressure from ischemia by reperfusion was 34.4% in the control, while in the presence of EGCg (3x10(-5) M) or GCg (3x10(-6) M, a more diluted concentration than that of EGCg), it led to a maximal increase of 78.4% or 76.2%, consistent with a significant preservative effect on the tissue level of ATP at the end of ischemia or reperfusion. In the perfused preparation of mitochondria, EGCg (10(-5) M) inhibited mitochondrial Ca(2+) elevation by changes in the Ca(2+) content or the acidification of perfusate, similarly to findings with cyclosporin A, a well known inhibitor of the mitochondrial permeability transition pore. By in vitro electron paramagnetic resonance (EPR), EGCg or GCg was found to directly quench the activity of active oxygen radicals, with the strongest activity in tea catechins. EGCg or GCg decreased the caspase-3 activity induced apoptosis. Therefore, it is concluded that the beneficial effects of EGCg or GCg play an important role in ischemia-reperfusion hearts in close relation with nitric oxide (NO), active oxygen radicals and biological redox systems in mitochondria. 相似文献
998.
Kanai M Higuchi K Hagihara T Konishi T Ishii T Fujita N Nakamura Y Maeda Y Yoshiba M Tadano T 《The New phytologist》2007,176(3):572-580
Common reed (Phragmites australis) is a well known salt-tolerant plant and it is suggested that reeds recover Na(+) in the xylem sap of the shoot base (basal part of the shoot), store it temporarily in the shoot base, release it into the phloem sap, and then retranslocate it to the roots. To investigate whether Na(+) is retained in the shoot base of reeds, confocal laser scanning microscope (CLSM) observations were conducted using an intracellular Na(+)-specific fluorescent probe. The CLSM observations revealed that reeds produced a large number of the starch granules at the shoot base when salt-stressed, and that the fluorescence indicating the location of intracellular free Na(+) was observed in the same position as the starch granules. The Na content of starch granules was considerably greater than that of the shoot base, whereas the potassium (K) contents of the granules was only slightly greater than that of the shoot base. Reeds produced Na(+)-binding starch granules in the parenchyma cells of the shoot base when salt-stressed; these starch granules may decrease intracellular free Na(+). It is proposed that the site-specific production of Na(+)-binding starch granules constitutes a novel salt tolerance mechanism. 相似文献
999.
Phytochromes are light responsive photoreceptors in plants that influence development and differentiation during the entire
plant life cycle. Plant nucleoside diphosphate kinase 2 (NDPK2) has been reported to be a component of the light-mediated
signalling cascade and to interact physically with phytochrome A in the cytosol. By using diverse methods as in vitro imports,
in vivo localisation of GFP-fusion proteins and immuno blotting of plant cell fractions we clearly localise NDPK2 only to
chloroplasts but not to the cytosol, demonstrating that although high affinity protein–protein interactions can occur in vitro,
their physiological relevance can be artificial if the proteins are localised to different cell compartments in vivo. 相似文献
1000.
Arabidopsis thaliana and Cuscuta spec. represent a compatible host–parasite combination. Cuscuta produces a haustorium that penetrates the host tissue. In early stages of development the searching hyphae on the tip of
the haustorial cone are connected to the host tissue by interspecific plasmodesmata. Ten days after infection, translocation
of the fluorescent dyes, Texas Red (TR) and 5,6-carboxyfluorescein (CF), demonstrates the existence of a continuous connection
between xylem and phloem of the host and parasite. Cuscuta becomes the dominant sink in this host–parasite system. Transgenic Arabidopsis plants expressing genes encoding the green fluorescent protein (GFP; 27 kDa) or a GFP–ubiquitin fusion (36 kDa), respectively,
under the companion cell (CC)-specific AtSUC2 promoter were used to monitor the transfer of these proteins from the host sieve elements to those of Cuscuta. Although GFP is transferred unimpedly to the parasite, the GFP–ubiquitin fusion could not be detected in Cuscuta. A translocation of the GFP–ubiquitin fusion protein was found to be restricted to the phloem of the host, although a functional
symplastic pathway exists between the host and parasite, as demonstrated by the transport of CF. These results indicate a
peripheral size exclusion limit (SEL) between 27 and 36 kDa for the symplastic connections between host and Cuscuta sieve elements. Forty-six accessions of A.
thaliana covering the entire range of its genetic diversity, as well as Arabidopsis
halleri, were found to be susceptible towards Cuscuta
reflexa. 相似文献