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111.
Alves-Gomes JA; Orti G; Haygood M; Heiligenberg W; Meyer A 《Molecular biology and evolution》1995,12(2):298-318
The order Gymnotiformes (South American electric fishes) is a fascinating
assemblage of freshwater fishes that share the unusual ability to produce
and sense electric fields used for electrolocation and social
communication. In the last few decades, the electrogenic and electrosensory
systems (EES) of these fish have served as an excellent model to study
motor and sensory physiology in vertebrates. In an attempt to the evolution
of characters associated with the EES in the group, we applied
maximum-parsimony (MP), minimum-evolution (ME), and maximum-likelihood (ML)
methods to analyze 302 aligned bases of the mitochondrial 12S rRNA and 416
bases of the mitochondrial 16S rRNA of 19 gymnotiform genera representing
all six recognized families. Six catfish genera (order Siluriformes) were
also sequenced and used as outgroups. The phylogenetic hypothesis resultant
from molecular data analysis differs in some respects from previous
hypotheses based on morphological studies. Our results were most
informative within the family level, as we were unable to elucidate the
relationships among deeper branches in this order with sufficient
confidence by using molecular data alone. The phylogenetic information of
both mitochondrial DNA segments appears to be affected by functional
constraints, and the resultant topologies were sensitive to different
weighting schemes and the algorithm used. Nonetheless, we found unanimous
support for the following phylogenetic relationships: (1) the family
Sternopygidae is an unnatural group, and Sternopygus is the sole
representative of a unique lineage within the order; (2) the family
Hypopomidae is not monophyletic; and (3) the order Gymnotiformes is
composed of at least six natural clades: Sternopygus, family Apteronotidae,
a new clade consisting of the remaining sternopygids, families Hypopomidae
+ Rhamphicthyidae, family Electrophoridae, and family Gymnotidae. By
combining molecular, morphological, and physiological information, we
propose a new hypothesis for the phylogeny of this group and suggest a new
family Eigenmanniidae n. (order Gymnotiformes).
相似文献
112.
Yescas CP MA Segura C L Martínez C VP Álvarez R JA Montemayor T JA Orozco V JE Frías R 《Phyton》2015,84(2):272-279
The scarcity of water in arid and semiarid regions of the world is a problem that every day increases by climate change. The subsurface drip irrigation (SDI) and changes in population density of plants are alternatives that can be used to make a sustainable use of water. Therefore, the objectives of this study were to determine the combination that allows for an increased corn performance and efficient use of water without losing the quality of forage. Three different irrigation levels were applied through a system of a SDI at three different densities of forage maize plants in an arid region. The results demonstrated that by applying different levels of water, either enough or lack of soil moisture is created, which is directly reflected in crop yield, and its determining variables such as green forage and dry matter yield, and nutritional quality. The irrigation level to a 100% of potential evapotranspiration (PET), at a density of 80000 plants/ha, increased yield of green forage to 57664 kg/ha; crude protein was 8.59%, while the rest of the quality parameters decreased. This study allowed to conclude that the irrigation level was the major factor in the response of the crop. 相似文献
113.
Kathryn E Wheatley Corey JA Bradshaw Robert G Harcourt Lloyd S Davis Mark A Hindell 《BMC veterinary research》2006,2(1):1-8
Background
Postweaning diarrhoea (PWD) in pigs is usually the main infectious problem of large-scale farms and is responsible for significant losses worldwide. The disease is caused mainly by enterotoxigenic E. coli (ETEC) and Shiga-toxin producing E. coli (STEC). In this study a total of 101 E. coli isolated from pigs with PWD in Slovakia were characterized using phenotypic and genotypic methods.Results
These 101 isolates belonged to 40 O:H serotypes. However, 57% of the isolates belonged to only six serotypes (O9:H51, O147:H-, O149:H10, O163:H-, ONT:H-, and ONT:H4), including two new serotypes (O163:H- and ONT:H4) not previously found among porcine ETEC and STEC isolated in other countries. Genes for EAST1, STb, STa, LT and Stx2e toxins were identified in 64%, 46%, 26%, 20%, and 5% of isolates, respectively. PCR showed that 35% of isolates carried genes for F18 colonization factor, and further analyzed by restriction endonuclease revealed that all of them were F18ac. Genes for F4 (K88), F6 (P987), F17, F5 (K99), F41, and intimin (eae gene) adhesins were detected in 19 %, 5%, 3%, 0.9%, 0.9%, and 0.9% of the isolates, respectively. The study of genetic diversity, carried out by PFGE of 46 representative ETEC and STEC isolates, revealed 36 distinct restriction profiles clustered in eight groups. Isolates of the same serotype were placed together in the dendrogram, but high degree of polymorphism among certain serotypes was detected.Conclusion
Seropathotype O149:H10 LT/STb/EAST1/F4 (14 isolates) was the most commonly detected followed by O163:H- EAST1/F18 (six isolates), and ONT:H4 STa/STb/Stx2e/F18 (five isolates). Interestingly, this study shows that two new serotypes (O163:H- and ONT:H4) have emerged as pig pathogens in Slovakia. Furthermore, our results show that there is a high genetic variation mainly among ETEC of O149:H10 serotype. 相似文献114.
Christopher JA Finnis Tom Payne Joanna Hay Neil Dodsworth Diane Wilkinson Philip Morton Malcolm J Saxton David J Tooth Robert W Evans Hans Goldenberg Barbara Scheiber-Mojdehkar Nina Ternes Darrell Sleep 《Microbial cell factories》2010,9(1):1-11
Background
Microorganisms that are exposed to pollutants in the environment, such as metals/metalloids, have a remarkable ability to fight the metal stress by various mechanisms. These metal-microbe interactions have already found an important role in biotechnological applications. It is only recently that microorganisms have been explored as potential biofactories for synthesis of metal/metalloid nanoparticles. Biosynthesis of selenium (Se0) nanospheres in aerobic conditions by a bacterial strain isolated from the coalmine soil is reported in the present study.Results
The strain CM100B, identified as Bacillus cereus by morphological, biochemical and 16S rRNA gene sequencing [GenBank:GU551935.1] was studied for its ability to generate selenium nanoparticles (SNs) by transformation of toxic selenite (SeO3 2-) anions into red elemental selenium (Se0) under aerobic conditions. Also, the ability of the strain to tolerate high levels of toxic selenite ions was studied by challenging the microbe with different concentrations of sodium selenite (0.5 mM-10 mM). ESEM, AFM and SEM studies revealed the spherical Se0 nanospheres adhering to bacterial biomass as well as present as free particles. The TEM microscopy showed the accumulation of spherical nanostructures as intracellular and extracellular deposits. The deposits were identified as element selenium by EDX analysis. This is also indicated by the red coloration of the culture broth that starts within 2-3 h of exposure to selenite oxyions. Selenium nanoparticles (SNs) were further characterized by UV-Visible spectroscopy, TEM and zeta potential measurement. The size of nanospheres was in the range of 150-200 nm with high negative charge of -46.86 mV.Conclusions
This bacterial isolate has the potential to be used as a bionanofactory for the synthesis of stable, nearly monodisperse Se0 nanoparticles as well as for detoxification of the toxic selenite anions in the environment. A hypothetical mechanism for the biogenesis of selenium nanoparticles (SNs) involving membrane associated reductase enzyme(s) that reduces selenite (SeO3 2-) to Se0 through electron shuttle enzymatic metal reduction process has been proposed. 相似文献115.
116.
Guillermo A. Logarzo Eduardo G. Virla Erica Luft Albarracin Serguei V. Triapitsyn Walker A. Jones Jesse H. de León Juan A. Briano 《BioControl》2012,57(1):37-48
The South American egg parasitoid Gonatocerus sp. near tuberculifemur “Clade 1” (G. sp. “Clade 1”) (Hymenoptera: Mymaridae) is a new association of the glassy-winged sharpshooter (GWSS), Homalodisca
vitripennis (Germar) (Cicadellidae) and a candidate for its biological control in California, USA. In Argentina, G. sp. “Clade 1” was screened in the laboratory (no-choice tests) and in the field (multiple choice tests) against eggs of 32
Auchenorrhyncha host species and other four potential hosts unrelated to sharpshooters. In no-choice assays, it parasitized
only eggs within the leafhopper tribe Proconiini. In contrast, in the long term field tests, it emerged not only from eggs
of the Proconiini but also from two species of Cicadellini at low numbers (five wasps out of 698 exposed eggs). Two interpretations
arise from the results: (1) Host associations of G. sp. “Clade 1” are restricted to the Proconiini whereas field parasitization of the Cicadellini species were false positive,
or (2) G. sp. “Clade 1” parasitizes also some Cicadellini species and its rejection in the laboratory was a false negative. Both interpretations
are discussed. Insect motivation could be the explanation for the negative results in the no-choice tests. On the other hand,
in the more natural field situations, the host selection process and oviposition behavior should not have been affected and
host range would be more realistic. The parasitism of the Cicadellini species would be indicative of a potential non-target
effect on the sharpshooters in the USA. 相似文献
117.
A reassessment of decreased amino acid accumulation by ehrlich ascites tumor cells in the presence of metabolic inhibitors 总被引:2,自引:0,他引:2 下载免费PDF全文
This study was undertaken to examine the mechanism by which metabolic inhibition reduces amino acid active transport in ehrlich ascites tumor cells. At 37 degrees C the metabolic inhibitor combination 0.1 mM 2,4-dinitrophenol (DNP) + 10 mM 2- deoxy-D-glucose (DOG) reduced the cell ATP concentration to 0.10- 0.15 mM in less than 5 min. This inhibition was associated with a 20.6 percent +/- 6.4 percent (SD) decrease in the initial influx of α-aminoisobutyric acid (AIB), and a two- to fourfold increase in the unidirectional efflux. These effects could be dissociated from changes in cell Na(+) or K(+) concentrations. Cells incubated to the steady state in 1.0-1.5 mM AIB showed an increased steady-state flux in the presence of DNP + DOG. Steady- state fluxes were consistent with trans-inhibition of AIB influx and trans-stimulation of efflux in control cells, but trans- stimulation of both fluxes in inhibited cells. In spite of the reduction of the cell ATP concentration to less than 0.15 mM and greatly reduced transmembrane concentration gradients of Na(+) and K(+), cells incubated to the steady state in the presence of the inhibitors still established an AIB distribution ration 13.8 +/- 2.6. The results are interpreted to indicate that a component of the reduction of AIB transport produced by metabolic inhibition is attributable to other actions in addition to the reduction of cation concentration gradients. Reduction of cell ATP alone is not responsible for the effects of metabolic inhibition, and both the transmembrane voltage and direct coupling to substrate oxidation via plasma-membrane-bound enzymes must be considered as possible energy sources for amino acid active transport. 相似文献
118.
Tenascin in the human intervertebral disc: alterations with aging and disc degeneration 总被引:1,自引:0,他引:1
Our objective for this study was to determine the presence and distribution of tenascin in the human intervertebral disc. The tenascins are a family of extracellular matrix proteins with repeated structural domains homologous to epidermal growth factor, fibronectin type III and the fibrinogens. Little is known about the presence of this protein in the disc. Ten normal human discs donated from subjects newborn to 15 years old, 10 control discs from adult donors aged 24-41 years, and 11 surgical disc specimens from patients aged 26-76 years were examined for immunolocalization of tenascin. In young discs, tenascin was localized throughout the annulus; in the nucleus, localization was confined to pericellular matrix. In adult control and degenerating disc specimens, tenascin in the annulus was localized primarily in pericellular matrix regions encircling either single cells or clusters of disc cells; in rare instances localization was more diffuse in the intraterritorial matrix. In young, healthy disc, tenascin was abundant throughout the annulus. In contrast, degenerating discs in adults showed a localization restricted to the pericellular, and rarely, more restricted intraterritorial matrix. These observations indicate that changes in the amount and distribution of tenascin may have a role in disc aging and degeneration, possibly by modulating fibronectin-disc-cell interactions, and causing alterations in the shape of disc cells. 相似文献
119.
Survey of Malassezia sp and dermatophytes in the cutaneous microbiome of free‐ranging golden‐headed lion tamarins (Leontopithecus chrysomelas ‐ Kuhl, 1820) 下载免费PDF全文
120.
Microfilaments and tropomyosin of cultured mammalian cells: isolation and characterization 总被引:4,自引:3,他引:4 下载免费PDF全文
Microfilaments were isolated from cultured mammalian cells, utilizing procedures similar to those for isolation of "native" thin filaments from muscle. Isolated microfilaments from rat embryo, baby hamster kidney (BHK- 21), and Swiss mouse 3T3 cells appeared structurally similar to muscle thin filaments, exhibiting long, 6 nm Diam profiles with a beaded, helical substructure. An arrowhead pattern was observed after reaction of isolated microfilaments with rabbit skeletal muscle myosin subfragment 1. Under appropriate conditions, isolated microfilaments will aggregate into a form that resembles microfilament bundles seen in situ cultured cells. Isolated microfilaments represent a complex of proteins including actin. Some of these components have been tentatively identified, based on coelectrophoresis with purified proteins, as myosin, tropomyosin, and a high molecular weight actin-binding protein. The tropomyosin components of isolated microfilaments were unexpected; polypeptides comigrated on SDS-polyacrylamide gels with both muscle and nonmuscle types of tropomyosin. In order to identify more specifically these subunits, we isolated and partially characterized tropomyosin from three cell types. BHK-21 cell tropomyosin was similar to other nonmuscle tropomyosins, as judged by several criteria. However, tropomyosin isolated from rate embryo and 3T3 cells contained subunits that comigrated with both skeletal muscle and nonmuscle types of myosin, whereas the BHK cell protein consistently contained a minor muscle-like subunit. The array of tropomyosin subunits present in a cell culture was reflected in the polypeptide chain pattern seen on SDS-polyacrylamide gels of microfilaments isolated from that culture. These studies provide a starting point for correlating changes in the ultrastructural organization of microfilaments with alterations in their protein composition. 相似文献