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701.
Halocins: are they involved in the competition between halobacteria in saltern ponds? 总被引:1,自引:0,他引:1
Many representatives of the family Halobacteriaceae ("halobacteria") excrete halophilic bacteriocins (halocins) that inhibit the growth of other halobacteria. In spite of the
fact that halocin production is widespread among the Halobacteriaceae, no information is available on their ecological significance. To test whether halocins may play a role in the interspecies
competition between dif-ferent types of halobacteria in saltern crystallizer ponds inhabited by dense communities of these
red halophiles, we assayed for halocins active against a variety of halobacteria in salterns from different locations worldwide.
Detection of halocin activity was based on the inhibition of growth of indicator organisms on agar plates, the decreased incorporation
of radiolabeled substrates, and microscopic examinations. No halocin activity was detected in any of the brines examined,
in spite of the fact that halocin production was demonstrated in cultures of most microorganisms isolated from these brines.
Thus, the contribution of halocins in the competition between different halobacteria in hypersaline aquatic environments is
probably negligible.
Received: July 29, 1999 / Accepted: October 18, 1999 相似文献
702.
Mogensen CE Neldam S Tikkanen I Oren S Viskoper R Watts RW Cooper ME 《BMJ (Clinical research ed.)》2000,321(7274):1440-1444
703.
Peter DA Alemu Y Xenos M Weisberg O Avneri I Eshkol M Oren T Elazar M Assaf Y Bluestein D 《Journal of biomechanical engineering》2012,134(4):041001
Drug-resistant hypertensive patients may be treated by mechanical stimulation of stretch-sensitive baroreceptors located in the sinus of carotid arteries. To evaluate the efficacy of endovascular devices to stretch the carotid sinus such that the induced strain might trigger baroreceptors to increase action potential firing rate and thereby reduce systemic blood pressure, numerical simulations were conducted of devices deployed in subject-specific carotid models. Two models were chosen--a typical physiologic carotid and a diminutive atypical physiologic model representing a clinically worst case scenario--to evaluate the effects of device deployment in normal and extreme cases, respectively. Based on the anatomical dimensions of the carotids, two different device sizes were chosen out of five total device sizes available. A fluid structure interaction (FSI) simulation methodology with contact surface between the device and the arterial wall was implemented for resolving the stresses and strains induced by device deployment. Results indicate that device deployment in the carotid sinus of the physiologic model induces an increase of 2.5% and 7.5% in circumferential and longitudinal wall stretch, respectively, and a maximum of 54% increase in von Mises arterial stress at the sinus wall baroreceptor region. The second device, deployed in the diminutive carotid model, induces an increase of 6% in both circumferential and longitudinal stretch and a 50% maximum increase in von Mises stress at the sinus wall baroreceptor region. Device deployment has a minimal effect on blood-flow patterns, indicating that it does not adversely affect carotid bifurcation hemodynamics in the physiologic model. In the smaller carotid model, deployment of the device lowers wall shear stress at sinus by 16% while accelerating flow entering the external carotid artery branch. Our FSI simulations of carotid arteries with deployed device show that the device induces localized increase in wall stretch at the sinus, suggesting that this will activate baroreceptors and subsequently may control hypertension in drug-resistant hypertensive patients, with no consequential deleterious effects on the carotid sinus hemodynamics. 相似文献
704.
In a metagenomic analysis of a stratified hypersaline (9?% salt) microbial mat in Guerrero Negro, Mexico, Kunin et al. (Mol Systems Biol 4:198, 2008) detected a significantly acid-shifted proteome, and concluded that adaptation by enriching proteins with acidic amino acids is more widespread than previously assumed. We here reevaluate these data and conclusions by comparing the isoelectric point profiles of the Guerrero Negro microbial mats (average isoelectric point 6.8) with those of the proteins encoded by the genomes of prokaryotes adapted to different salt concentrations ranges and belonging to different phylogenetic and physiological groups. Average isoelectric points below 6.8 were found not only in the proteomes of the moderately halophilic aerobic bacteria Halomonas elongata and Chromohalobacter salexigens, but even in common types of marine bacteria of the genera Alteromonas and Aliivibrio. We did not find clear evidence that the isoelectric point profile of the Guerrero Negro microbial mat can be considered to be the result of species-independent molecular convergence of the members of the microbial community determined by the salinity of the overlaying brine. 相似文献
705.
We performed a comparative analysis of the genome sequences of three anaerobic halophilic fermentative bacteria belonging to the order Halanaerobiales: Halanaerobium praevalens, the alkaliphilic "Halanaerobium hydrogeniformans", and the thermophilic Halothermothrix orenii to assess the amino acid composition of their proteins. Members of the Halanaerobiales were earlier shown to accumulate KCl rather than organic compatible solutes for osmotic balance, and therefore the presence of a dominantly acidic proteome was predicted. Past reports indeed showed a large excess of acidic over basic amino acids in whole-cell hydrolysates of selected members of the order. However, the genomic analysis did not show unusually high contents of acidic amino acids or low contents of basic amino acids. The apparent excess of acidic amino acids in these anaerobic halophiles reported earlier is due to the high content in their proteins of glutamine and asparagine, which yield glutamate and aspartate upon acid hydrolysis. It is thus suggested that the proteins of the Halanaerobiales, which are active in the presence of high intracellular KCl concentrations, do not possess the typical acidic signature of the 'halophilic' proteins of the Archaea of the order Halobacteriales or of the extremely halophilic bacterium Salinibacter. 相似文献
706.
Loh XJ del Barrio J Toh PP Lee TC Jiao D Rauwald U Appel EA Scherman OA 《Biomacromolecules》2012,13(1):84-91
The synthesis of a supramolecular double hydrophilic block copolymer (DHBC) held together by cucurbit[8]uril (CB[8]) ternary complexation and its subsequent self-assembly into micelles is described. This system is responsive to multiple external triggers including temperature, pH and the addition of a competitive guest. The supramolecular block copolymer assembly consists of poly(N-isopropylacrylamide) (PNIPAAm) as a thermoresponsive block and poly(dimethylaminoethylmethacrylate) (PDMAEMA) as a pH-responsive block. Moreover, encapsulation and controlled drug release was demonstrated with this system using the chemotherapeutic drug doxorubicin (DOX). This triple stimuli-responsive DHBC micelle system represents an evolution over conventional double stimuli-responsive covalent diblock copolymer systems and displayed a significant reduction in the viability of HeLa cells upon triggered release of DOX from the supramolecular micellar nanocontainers. 相似文献
707.
Halimah Sayahi Kaitlin M. Pugliese Oren Zimhony William R. Jacobs Jr. Alexander Shekhtman John T. Welch 《化学与生物多样性》2012,9(11):2582-2596
Analogs of pyrazinamide (=pyrazine‐2‐carboxamide; PZA), an essential component of short‐course antituberculous chemotherapy, such as 5‐chloropyrazinamide (5‐Cl‐PZA) act as competitive inhibitors of NADPH binding to purified mycobacterial fatty acid synthase I (FAS I) as shown by Saturation Transfer Difference (STD) NMR studies. In addition, pyrazinoic acid esters (POE) and 5‐Cl‐POE reversibly bind to FAS I with the relatively greater affinity of longer‐chain esters for FAS I, clear from the STD amplification factors. The competitive binding of PZA and 5‐Cl‐PZA clearly illustrates that both agents bind FAS. In contrast to PZA, at low NADPH concentrations 5‐Cl‐PZA is a cooperative inhibitor of NADPH binding. 相似文献
708.
Erik?Caroselli Guido?Mattioli Oren?Levy Giuseppe?Falini Zvy?Dubinsky Stefano?GoffredoEmail author 《Frontiers in zoology》2012,9(1):32
Introduction
Correlations between sea surface temperature (SST) and growth parameters of the solitary azooxanthellate Dendrophylliid Leptopsammia pruvoti were assessed along an 8° latitudinal gradient on western Italian coasts (Mediterranean Sea), to check for possible negative effects of increasing temperature as the ones reported for a closely related, sympatric but zooxanthellate species.Results
Calcification rate was correlated with skeletal density but not with linear extension rate, indicating that calcium carbonate deposition was preferentially allocated to keep a constant skeletal density. Unlike most studies on both temperate and tropical zooxanthellate corals, where calcification rate is strongly related to environmental parameters such as SST, in the present study calcification rate was not correlated with SST.Conclusions
The lower sensitivity of L. pruvoti to SST with respect to other sympatric zooxanthellate corals, such as Balanophyllia europaea, may rely on the absence of a temperature induced inhibition of photosynthesis, and thus the absence of an inhibition of the calcification process. This study is the first field investigation of the relationship between SST and the three growth parameters of an azooxanthellate coral. Increasing research effort on determining the effects of temperature on biological traits of the poorly studied azooxanthellate scleractinians may help to predict the possible species assemblage shifts that are likely to occur in the immediate future as a consequence of global climatic change.709.
David S. Ellsworth Richard Thomas Kristine Y. Crous Sari Palmroth Eric Ward Chris Maier Evan DeLucia Ram Oren 《Global Change Biology》2012,18(1):223-242
Leaf responses to elevated atmospheric CO2 concentration (Ca) are central to models of forest CO2 exchange with the atmosphere and constrain the magnitude of the future carbon sink. Estimating the magnitude of primary productivity enhancement of forests in elevated Ca requires an understanding of how photosynthesis is regulated by diffusional and biochemical components and up‐scaled to entire canopies. To test the sensitivity of leaf photosynthesis and stomatal conductance to elevated Ca in time and space, we compiled a comprehensive dataset measured over 10 years for a temperate pine forest of Pinus taeda, but also including deciduous species, primarily Liquidambar styraciflua. We combined over one thousand controlled‐response curves of photosynthesis as a function of environmental drivers (light, air Ca and temperature) measured at canopy heights up to 20 m over 11 years (1996–2006) to generate parameterizations for leaf‐scale models for the Duke free‐air CO2 enrichment (FACE) experiment. The enhancement of leaf net photosynthesis (Anet) in P. taeda by elevated Ca of +200 μmol mol?1 was 67% for current‐year needles in the upper crown in summer conditions over 10 years. Photosynthetic enhancement of P. taeda at the leaf‐scale increased by two‐fold from the driest to wettest growing seasons. Current‐year pine foliage Anet was sensitive to temporal variation, whereas previous‐year foliage Anet was less responsive and overall showed less enhancement (+30%). Photosynthetic downregulation in overwintering upper canopy pine needles was small at average leaf N (Narea), but statistically significant. In contrast, co‐dominant and subcanopy L. styraciflua trees showed Anet enhancement of 62% and no Anet–Narea adjustments. Various understory deciduous tree species showed an average Anet enhancement of 42%. Differences in photosynthetic responses between overwintering pine needles and subcanopy deciduous leaves suggest that increased Ca has the potential to enhance the mixed‐species composition of planted pine stands and, by extension, naturally regenerating pine‐dominated stands. 相似文献
710.
M Garber N Yosef A Goren R Raychowdhury A Thielke M Guttman J Robinson B Minie N Chevrier Z Itzhaki R Blecher-Gonen C Bornstein D Amann-Zalcenstein A Weiner D Friedrich J Meldrim O Ram C Cheng A Gnirke S Fisher N Friedman B Wong BE Bernstein C Nusbaum N Hacohen A Regev I Amit 《Molecular cell》2012,47(5):810-822