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141.
Background
The Burkholderia cepacia complex (Bcc) is a collection of nine genotypically distinct but phenotypically similar species. They show wide ecological diversity and include species that are used for promoting plant growth and bio-control as well species that are opportunistic pathogens of vulnerable patients. Over recent years the Bcc have emerged as problematic pathogens of the CF lung. Pseudomonas aeruginosa is another important CF pathogen. It is able to synthesise hydrogen cyanide (HCN), a potent inhibitor of cellular respiration. We have recently shown that HCN production by P. aeruginosa may have a role in CF pathogenesis. This paper describes an investigation of the ability of bacteria of the Bcc to make HCN. 相似文献142.
Ecosystem Respiration in a Cool Temperate Bog Depends on Peat Temperature But Not Water Table 总被引:1,自引:0,他引:1
Ecosystem respiration (ER) is an important but poorly understood part of the carbon (C) budget of peatlands and is controlled
primarily by the thermal and hydrologic regimes. To establish the relative importance of these two controls for a large ombrotrophic
bog near Ottawa, Canada, we analyzed ER from measurements of nighttime net ecosystem exchange of carbon dioxide (CO2) determined by eddy covariance technique. Measurements were made from May to October over five years, 1998 to 2002. Ecosystem
respiration ranged from less than 1 μmol CO2 m−2 s−1 in spring (May) and fall (late October) to 2–4 μmol CO2 m−2 s−1 during mid-summer (July-August). As anticipated, there was a strong relationship between ER and peat temperatures (r2 = 0.62). Q10 between 5° to 15°C varied from 2.2 to 4.2 depending upon the choice of depth where temperature was measured and location
within a hummock or hollow. There was only a weak relationship between ER and water-table depth (r2 = 0.11). A laboratory incubation of peat cores at different moisture contents showed that CO2 production was reduced by drying in the surface samples, but there was little decrease in production due to drying from below
a depth of 30 cm. We postulate that the weak correlation between ER and water table position in this peatland is primarily
a function of the bog being relatively dry, with water table varying between 30 and 75 cm below the hummock tops. The dryness
gives rise to a complex ER response to water table involving i) compensations between production of CO2 in the upper and lower peat profile as the water table falls and ii) the importance of autotrophic respiration, which is
relatively independent of water-table position. 相似文献
143.
Michel Lafleur Lesley Courtemanche Katarina Edwards Puttaswamy Manjunath 《Biochemical and biophysical research communications》2010,399(3):406-411
Binder-of-sperm (BSP) proteins interact with sperm membranes and are proposed to extract selectively phosphatidylcholine and cholesterol from these. This change in lipid composition is a key step in sperm capacitation. The present work demonstrates that the interactions between the protein BSP1 and model membranes composed with phosphatidylcholine lead to drastic changes in the morphology of the lipidic self-assemblies. Using cryo-electron microscopy and fluorescence microscopy, we show that, in the presence of the protein, the lipid vesicles elongate, and form bead necklace-like structures that evolve toward small vesicles or thread-like structures. In the presence of multilamellar vesicles, where a large reservoir of lipid is available, the presence of BSP proteins lead to the formation of long nanotubes. Long spiral-like threads, associated with lipid/protein complexes, are also observed. The local curvature of lipid membranes induced by the BSP proteins may be involved in lipid domain formation and the extraction of some lipids during the sperm maturation process. 相似文献
144.
Phosphorus NMR spectroscopy was used to characterize the importance of electrostatic interactions in the lytic activity of melittin, a cationic peptide. The micellization induced by melittin has been characterized for several lipid mixtures composed of saturated phosphatidylcholine (PC) and a limited amount of charged lipid. For these systems, the thermal polymorphism is similar to the one observed for pure PC: small comicelles are stable in the gel phase and extended bilayers are formed in the liquid crystalline phase. Vesicle surface charge density influences strongly the micellization. Our results show that the presence of negatively charged lipids (phospholipid or unprotonated fatty acid) reduces the proportion of lysed vesicles. Conversely, the presence of positively charged lipids leads to a promotion of the lytic activity of the peptide. The modulation of the lytic effect is proposed to originate from the electrostatic interactions between the peptide and the bilayer surface. Attractive interactions anchor the peptide at the surface and, as a consequence, inhibit its lytic activity. Conversely, repulsive interactions favor the redistribution of melittin into the bilayer, causing enhanced lysis. A quantitative analysis of the interaction between melittin and negatively charged bilayers suggests that electroneutrality is reached at the surface, before micellization. The surface charge density of the lipid layer appears to be a determining factor for the lipid/peptide stoichiometry of the comicelles; a decrease in the lipid/peptide stoichiometry in the presence of negatively charged lipids appears to be a general consequence of the higher affinity of melittin for these membranes. 相似文献
145.
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147.
Michael M. Loranty Scott J. Goetz Edward B. Rastetter Adrian V. Rocha Gaius R. Shaver Elyn R. Humphreys Peter M. Lafleur 《Ecosystems》2011,14(1):76-93
We scale a model of net ecosystem CO2 exchange (NEE) for tundra ecosystems and assess model performance using eddy covariance measurements at three tundra sites.
The model, initially developed using instantaneous (seconds–minutes) chamber flux (~m2) observations, independently represents ecosystem respiration (ER) and gross primary production (GPP), and requires only
temperature (T), photosynthetic photon flux density (I
0), and leaf area index (L) as inputs. We used a synthetic data set to parameterize the model so that available in situ observations could be used to
assess the model. The model was then scaled temporally to daily resolution and spatially to about 1 km2 resolution, and predicted values of NEE, and associated input variables, were compared to observations obtained from eddy
covariance measurements at three flux tower sites over several growing seasons. We compared observations to modeled NEE calculated
using T and I
0 measured at the towers, and L derived from MODIS data. Cumulative NEE estimates were within 17 and 11% of instrumentation period and growing season observations,
respectively. Predictions improved when one site-year experiencing anomalously dry conditions was excluded, indicating the
potential importance of stomatal control on GPP and/or soil moisture on ER. Notable differences in model performance resulted
from ER model formulations and differences in how L was estimated. Additional work is needed to gain better predictive ability
in terms of ER and L. However, our results demonstrate the potential of this model to permit landscape scale estimates of
NEE using relatively few and simple driving variables that are easily obtained via satellite remote sensing. 相似文献
148.
Kumar Narayanan Mohammed Omer Mohammed Arif Papani Sridhar Nitin Annarapu Shivaprasad Naidu Pankaj Jariwala Narasaraju Kavalipati Mukharjee Madivada Ramagiri Balaji Premchand M Sharath Reddy A Anil Krishna G Padmakumar EA 《Indian pacing and electrophysiology journal》2021,21(1):5-10
BackgroundLeft-sided ablation, targeting left inferior AV nodal extensions, is thought to be necessary for success in a small proportion of atrioventricular nodal re-entrant tachycardia (AVNRT) ablations; however Indian data are scarce in this regard.MethodsConsecutive cases of AVNRT undergoing slow pathway ablation in a single centre over an 18-month period were retrospectively analyzed. Left-sided ablation at the posteroseptal mitral annulus was performed if right-sided ablation failed to abolish AVNRT.ResultsFrom January 2017 to June 2018, out of 215 consecutive supraventricular tachycardia (SVT) cases, 154 (71.6%) were AVNRT (47.1 ± 13.1 years, 46.1% male). Trans-septal ablation was required in 5 (3.2%) cases (mean age 48.8 ± 9.4 years; 4 female, 1 male); all with typical (slow-fast) form of AVNRT. Compared with cases needing only right-sided ablation, radiofrequency time (50.8 ± 16.9 vs. 9.9 ± 8.5 min; p = 0.005) and procedure time (166.0 ± 35.0 vs 79.6 ± 35.9 min; p = 0.004) were significantly longer for trans-septal cases, while baseline intervals and tachycardia cycle length were not significantly different. Junctional ectopy was seen in only 2 of the 5 cases during left-sided ablation, but acute success (non-inducibility) was obtained in 3 cases. There were no instances of AV block. Over mean follow-up of 12.2 ± 4.0 months, clinical recurrence of AVNRT occurred in one case, while others remained arrhythmia-free without medication.ConclusionLeft-sided ablation was required in a small proportion of AVNRT ablations. Trans-septal approach targeting the posteroseptal mitral annulus was safe and yielded good mid-term clinical success. 相似文献
149.
Oxidative radicals, which are produced during ionizing irradiation of DNA in water, damage the DNA and may result in mutations, which are in general randomly distributed. Alternatively, the addition of transition metal ions, like iron or copper, to DNA in combination with H(2)O(2) and a reducing agent also results in the production of oxidative radicals. Due to binding of the transition metal ions to DNA, the production of these radicals is very local, and results in a mutational spectrum in which the mutations are not randomly distributed. If transition metal ions are complexed to the DNA during irradiation, and react with radiation-induced species such as hydrogen peroxide, site-specific formation of.OH radicals on these sites may occur, leading to the formation of mutational hot spots. This study examines the influence of the presence of traces of iron or copper ions during gamma-irradiation of plasmid DNA in water, on the possible formation of mutational hot spots in the lacI gene. Comparison of the mutational spectra, after irradiation in the presence or in the absence of transition metal ions, shows that there are indeed relatively more positions in the lacI gene where more than one mutation occurs, suggesting formation of mutational hot spots in the presence of transition metal ions. However, the appearance of these hot spots is rather weak. Although in all three mutational spectra G:C to A:T mutations are predominant, there are also some differences between the types of mutations in these spectra. These differences in mutational spectra might reflect the different preferences of iron and copper ions to bind specific sites in the DNA. Indeed, there appears to be a high association of mutations at CC or GG sites in the mutational spectrum in the presence of copper ions, confirming the observation that copper binds preferably at two adjacent guanines in the DNA. It can be concluded from this study that the presence of small amounts of transition metal ions during gamma-irradiation influences the types and distribution of gamma-radiation-induced mutations, although no major mutational hot spots can be observed. 相似文献
150.