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1.
2.
Subtelomeric expression regions of Borrelia hermsii linear plasmids are highly polymorphic 总被引:10,自引:0,他引:10
B. I. Restrepo T. Kitten C.J. Carter D. Infante A. G. Barbour 《Molecular microbiology》1992,6(22):3299-3311
Borrelia hermsii, a relapsing fever agent, undergoes multiphasic antigenic variation to evade its host's immune response. Serotype specificity is determined by variable membrane lipoproteins, Vmps, which are expressed from genes located near the end of a linear plasmid. Using the polymerase chain reaction and primers representing the promoter of the active vmp and a conserved telomeric sequence, we characterized the subtelomeric expression regions of the 25 known serotypes of strain HS1. The distance from the promoter to the telomere fell into three size classes of approximately 1.0, 1.5, and 2.5 kilobases. In the sequenced serotypes the size differences were accounted for by variable lengths of the vmp genes and intervening sequences between 3' end of the vmp gene and the start of a downstream homology block. The degree of nucleotide identity between different vmp genes, or between the different 3' flanking DNA varied from 39-78%. Thus, there is length and sequence variability not only between vmp genes themselves but also between the 3' flanking regions of vmp genes. 相似文献
3.
Summary Methods are described which demonstrate the use of unidirectional influx of14C-tetraphenylphosphonium (14C-TPP+) into isolated intestinal epithelial cells as a quantitative sensor of the magnitude of membrane potentials created by experimentally imposed ion gradients. Using this technique the quantitative relationship between membrane potential () and Na+-dependent sugar influx was determined for these cells at various Na+ and -methylglucoside (-MG) concentrations. The results show a high degree of dependence for the transport Michaelis constant but a maximum velocity for transport which is independent of . No transinhibition by intracellular sugar (40mm) can be detected. Sugar influx in the absence of Na+ is insensitive to 1.3mm phlorizin and independent of . The mechanistic implications of these results were evaluated using the quality of fit between calculated and experimentally observed kinetic constants for rate equations derived from several transport models. The analysis shows that for models in which translocation is the potential-dependent step the free carrier cannot be neutral. If it is anionic, the transporter must be functionally asymmetric. A model in which Na+ binding is the potential-dependent step (Na+ well concept) also provides an appropriate kinetic fit to the experimental data, and must be considered as a possible mechanistic basis for function of the system. 相似文献
4.
A yeast-derived antigen from Paracoccidioides brasiliensis useful for serologic testing 总被引:2,自引:0,他引:2
Antigens prepared from P. brasiliensis yeast cells subjected to ultrasonic treatment proved reliable in the serological diagnosis of paracoccidioidomycosis. Detection of antibodies was possible in over 90% from paracoccidioidomycosis patients in tests with agar gel immunodiffusion and counterimmunoelectrophoresis. Specificity was high and only histoplasmosis sera produced cross reactions, albeit at a lower frequency (10%). The new antigens compared favorably to the standard yeast culture filtrate antigen used in the past and they have the advantage of being reproducible. Proper control of proteolysis is required if activity is to be preserved. 相似文献
5.
D Restrepo Y Okada J H Teeter L D Lowry B Cowart J G Brand 《Biophysical journal》1993,64(6):1961-1966
The sense of smell allows terrestrial animals to collect information about the chemical nature of their environment through the detection of airborne molecules. In humans smell is believed to play an important role in protecting the organism from environmental hazards such as fire, gas leaks and spoiled food, in determining the flavor of foods, and perhaps in infant-parent bonding. In addition, the study of human olfaction is relevant to a number of medical problems that result in olfactory dysfunction, which can affect nutritional state, and to the study of the etiology of neurodegenerative diseases which manifest themselves in the olfactory epithelium. Although much is known about behavioral aspects of human olfaction, little is understood about the underlying cellular mechanisms in humans. Here we report that viable human olfactory neurons (HON) can be isolated from olfactory tissue biopsies, and we find that HON respond to odorants with an increase in intracellular calcium concentration ([Cai]). 相似文献
6.
The postingestional effect of seed size and mass and nutrient composition on fruit profitability are reviewed. It is emphasized that profitability results from the interaction between fruit characteristics and the physiological and morphological traits of frugivores. The processes by which frugivores regurgitate or defecate seeds and the differential processing of the nutrient rich pulp and ballast in fruit are strongly dependent on the interaction between frugivore gut morphology and seed size. Euphonias that lack a functional gizzard defecate seeds, whereas tanagers that have a delete a functional gizzards regurgitate seeds. Some frugivores separate seeds from pulp and exocarp in the gizzard. It is hypothesized that the gizzard plays an important role in determining the postigestional fate of different pulp components. Although fruit nutrient content is often invoked as a determinant of frugivore feeding choices, studies that rely on proximal nutrient analysis, have often failed to find clear nutrient composition-preference correlations. It is argued that a partial reason for this failure is that proximal nutrient analysis ignores the complexities of fruit digestion. The ecological and physiological correlates of lipid and sugar assimilation are used to identify the limitations of traditional proximal nutrient analyses in fruit-frugivore studies. We suggest that recognizing the intricacies of the digestive characteristics of frugivores may reveal a much richer patterning in the interaction of frugivores with plants than has been previously hypothesized. 相似文献
7.
Genetic variation at the Major Histocompatibility Complex locus DQ beta was
analyzed in 233 beluga whales (Delphinapterus leucas) from seven
populations: St. Lawrence Estuary, eastern Beaufort Sea, eastern Chukchi
Sea, western Hudson Bay, eastern Hudson Bay, southeastern Baffin Island,
and High Arctic and in 12 narwhals (Monodon monoceros) sympatric with the
High Arctic beluga population. Variation was assessed by amplification of
the exon coding for the peptide binding region via the polymerase chain
reaction, followed by either cloning and DNA sequencing or single-stranded
conformation polymorphism analysis. Five alleles were found across the
beluga populations and one in the narwhal. Pairwise comparisons of these
alleles showed a 5:1 ratio of nonsynonymous to synonymous substitutions per
site leading to eight amino acid differences, five of which were
nonconservative substitutions, centered around positions previously shown
to be important for peptide binding. Although the amount of allelic
variation is low when compared with terrestrial mammals, the nature of the
substitutions in the peptide binding sites indicates an important role for
the DQ beta locus in the cellular immune response of beluga whales.
Comparisons of allele frequencies among populations show the High Arctic
population to be different (P < or = .005) from the other beluga
populations surveyed. In these other populations an allele, Dele-DQ
beta*0101-2, was found in 98% of the animals, while in the High Arctic it
was found in only 52% of the animals. Two other alleles were found at high
frequencies in the High Arctic population, one being very similar to the
single allele found in narwhal.
相似文献
8.
Survival of Paracoccidioides brasiliensis yeast cells under microaerophilic conditions 总被引:1,自引:0,他引:1
The ability of P. brasiliensis yeast cells to withstand microaerophilic conditions was investigated in a liquid medium distributed in tall columns in screw-capped tubes. Young cells of three isolates were inoculated on top of the medium, and the tubes were incubated aerobically and anaerobically at 36 degrees C for 28 days. The viability of cells that had sedimented to the bottoms of the tubes was studied by fluorescent microscopy and by their capacity to resume growth when transferred to fresh medium under continuous agitation. The proportion of viable cells in the sediments diminished with time of incubation. However, after 28 days, 27% of the cells were still viable and fully capable of active growth when placed under adequate aeration. On the other hand, drastic reduction of oxygen access elicited an accelerated death rate, with no survival after 7 days of incubation. 相似文献
9.
Loren P. Albert Natalia Restrepo‐Coupe Marielle N. Smith Jin Wu Cecilia Chavana‐Bryant Neill Prohaska Tyeen C. Taylor Giordane A. Martins Philippe Ciais Jiafu Mao M. Altaf Arain Wei Li Xiaoying Shi Daniel M. Ricciuto Travis E. Huxman Sean M. McMahon Scott R. Saleska 《Global Change Biology》2019,25(11):3591-3608
Plant phenology—the timing of cyclic or recurrent biological events in plants—offers insight into the ecology, evolution, and seasonality of plant‐mediated ecosystem processes. Traditionally studied phenologies are readily apparent, such as flowering events, germination timing, and season‐initiating budbreak. However, a broad range of phenologies that are fundamental to the ecology and evolution of plants, and to global biogeochemical cycles and climate change predictions, have been neglected because they are “cryptic”—that is, hidden from view (e.g., root production) or difficult to distinguish and interpret based on common measurements at typical scales of examination (e.g., leaf turnover in evergreen forests). We illustrate how capturing cryptic phenology can advance scientific understanding with two case studies: wood phenology in a deciduous forest of the northeastern USA and leaf phenology in tropical evergreen forests of Amazonia. Drawing on these case studies and other literature, we argue that conceptualizing and characterizing cryptic plant phenology is needed for understanding and accurate prediction at many scales from organisms to ecosystems. We recommend avenues of empirical and modeling research to accelerate discovery of cryptic phenological patterns, to understand their causes and consequences, and to represent these processes in terrestrial biosphere models. 相似文献
10.
Johanna del Castillo-Múnera Martha Cárdenas Andrés Pinzón Adriana Castañeda Adriana J. Bernal Silvia Restrepo 《Revista iberoamericana de micología》2013,30(2):88-95
BackgroundPhytophthora is the most important genus of the Oomycete plant pathogens. Nowadays, there are 117 described species in this genus, most of them being primary invaders of plant tissues. The different species are causal agents of diseases in a wide range of crops and plants in natural environments. In order to develop control strategies against Phytophthoraspecies, it is important to know the biology, ecology and evolutionary processes of these important pathogens.AimsThe aim of this study was to propose and validate a low cost identification system for Phytophthora species based on a set of polymorphic microsatellite (SSRs) markers.MethodsThirty-three isolates representing Phytophthora infestans, Phytophthora andina, Phytophthora sojae, Phytophthora cryptogea, Phytophthora nicotianae, Phytophthora capsici and Phytophthora cinnamomi species were obtained, and 13 SSRs were selected as potentially transferable markers between these species. Amplification conditions, including annealing temperatures, were standardized for several markers.ResultsA subset of these markers amplified in all species, showing species-specific alleles.ConclusionsThe adaptability and impact of the identification system in Colombia, an Andean agricultural country where different Phytophthora species co-exist in the same or in several hosts grown together, are discussed. 相似文献