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1.
Aharon Gibor 《Protoplasma》1973,78(1-2):195-202
Summary The sterile whorls ofAcetabularia increase greatly the surface area of the cell. These structures function in the uptake of solutes from the environment. The development of the whorls is controlled by light and also by the availability of nutrients. 相似文献
2.
Gametes of the unicellular green alga Chlamydomonas reinhardii recognize and adhere to cells of the opposite mating type by flagellar contact. Adhesion between these specialized organelles signals a rapid series of mating events which result in gamete fusion. The sequence of morphological changes (flagellar tip activation, cell wall loss, and mating structure elongation), which occur as a consequence of the sexual signalling, have been characterized. The signalling mechanisms have, however, not been defined. Calcium is known to be involved during fertilization of animal species. Increased intracellular free calcium, which can be achieved either by calcium influx or by mobilization of ions from intracellular stores, has been observed during activation of both eggs and sperm. A recent report by Bloodgood & Levin that gametes of C. reinhardii preloaded with 45Ca showed a transient increase in Ca efflux following mating, suggests that intracellular Ca redistribution may also accompany mating in this algal species. We have used X-ray microanalysis to analyze the subcellular distribution of bound calcium during mating in Chlamydomonas reinhardii. X-ray maps reveal that calcium is sequestered in discrete granules within the gamete cell body prior to mating and that during activation and cell fusion, calcium is diffuse throughout the cell. This suggests the possibility that calcium serves as a second messenger in this species. 相似文献
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5.
Noga Kronfeld-Schor Davide Dominoni Horacio de la Iglesia Oren Levy Erik D. Herzog Tamar Dayan Charlotte Helfrich-Forster 《Proceedings. Biological sciences / The Royal Society》2013,280(1765)
Most studies in chronobiology focus on solar cycles (daily and annual). Moonlight and the lunar cycle received considerably less attention by chronobiologists. An exception are rhythms in intertidal species. Terrestrial ecologists long ago acknowledged the effects of moonlight on predation success, and consequently on predation risk, foraging behaviour and habitat use, while marine biologists have focused more on the behaviour and mainly on reproduction synchronization with relation to the Moon phase. Lately, several studies in different animal taxa addressed the role of moonlight in determining activity and studied the underlying mechanisms. In this paper, we review the ecological and behavioural evidence showing the effect of moonlight on activity, discuss the adaptive value of these changes, and describe possible mechanisms underlying this effect. We will also refer to other sources of night-time light (‘light pollution’) and highlight open questions that demand further studies. 相似文献
6.
The widely used pathway-based approach for interpreting Genome Wide Association Studies (GWAS), assumes that since function is executed through the interactions of multiple genes, different perturbations of the same pathway would result in a similar phenotype. This assumption, however, was not systemically assessed on a large scale. To determine whether SNPs associated with a given complex phenotype affect the same pathways more than expected by chance, we analyzed 368 phenotypes that were studied in >5000 GWAS. We found 216 significant phenotype-pathway associations between 70 of the phenotypes we analyzed and known pathways. We also report 391 strong phenotype-phenotype associations between phenotypes that are affected by the same pathways. While some of these associations confirm previously reported connections, others are new and could shed light on the molecular basis of these diseases. Our findings confirm that phenotype-associated SNPs cluster into pathways much more than expected by chance. However, this is true for <20% (70/368) of the phenotypes. Different types of phenotypes show markedly different tendencies: Virtually all autoimmune phenotypes show strong clustering of SNPs into pathways, while most cancers and metabolic conditions, and all electrophysiological phenotypes, could not be significantly associated with any pathway despite being significantly associated with a large number of SNPs. While this may be due to missing data, it may also suggest that these phenotypes could result only from perturbations of specific genes and not from other perturbations of the same pathway. Further analysis of pathway-associated versus gene-associated phenotypes is, therefore, needed in order to understand disease etiology and in order to promote better drug target selection. 相似文献
7.
Selective stabilization by the bacteriophage 434 repressor of the plasmid expressing bovine growth hormone in Escherichia coli. 下载免费PDF全文
The maintenance of a plasmid vector-host system that selects for bacteria carrying the plasmid without the need for antibiotics is described. In this system, the bacteriophage 434 repressor gene cloned on the plasmid protects the host from lysis by a lambda imm434 cI- prophage. Cells that occasionally lose the plasmid are killed by prophage induction and therefore do not accumulate in the growing culture. The presence of the phage 434 repressor in the cells does not interfere with the process of lambda repressor inactivation and the high-level production of bovine growth hormone. 相似文献
8.
Nikhil Ram-Mohan Aharon Oren R. Thane Papke 《Extremophiles : life under extreme conditions》2016,20(5):747-757
Stability of microbial communities can impact the ability of dispersed cells to colonize a new habitat. Saturated brines and their halophile communities are presumed to be steady state systems due to limited environmental perturbations. In this study, the bacteriorhodopsin-containing fraction of the haloarchaeal community from Eilat salt crystallizer ponds was sampled five times over 3 years. Analyses revealed the existence of a constant core as several OTUs were found repeatedly over the length of the study: OTUs comprising 52 % of the total cloned and sequenced PCR amplicons were found in every sample, and OTUs comprising 89 % of the total sequences were found in more than one, and often more than two samples. LIBSHUFF and UNIFRAC analyses showed statistical similarity between samples and Spearman’s coefficient denoted significant correlations between OTU pairs, indicating non-random patterns in abundance and co-occurrence of detected OTUs. Further, changes in the detected OTUs were statistically linked to deviations in salinity. We interpret these results as indicating the existence of an ever-present core bacteriorhodopsin-containing Eilat crystallizer community that fluctuates in population densities, which are controlled by salinity rather than the extinction of some OTUs and their replacement through immigration and colonization. 相似文献
9.
We have used fatty acid analyses to study the community structure of a layered endoevaporitic microbial community within a
gypsum crust that covers the bottom of a saltern evaporation pond in Eilat, Israel. This community, living at a salinity of
218–238 g l−1 total dissolved salts, consists of an upper brown layer dominated by unicellular cyanobacteria, a green layer with filamentous
cyanobacteria, a red-purple layer with both Chromatium and Ectothiorhodospira/Halorhodospira type of purple sulfur bacteria, and a black layer in which dissimilatory sulfate reduction occurs. An olive-green layer is
sometimes present below the red-purple layer. Analysis by gas chromatography/mass spectrometry of the fatty acid methyl esters
prepared from the different fractions showed characteristic patterns in each layer, and these could be related to fatty acid
composition data from the literature and to fatty acid analyses of representative halophilic microorganisms isolated from
the site. The nature of the fatty acids in the green layer suggests that the cyanobacteria present there use the oxygen-independent
pathway for production of unsaturated fatty acids, a pathway only occasionally encountered in filamentous cyanobacteria. The
facultative anaerobic nature of the cyanobacteria in the green layer was confirmed by their ability to perform anoxygenic
photosynthesis with sulfide as electron donor. Specific signature fatty acids identified for each layer corresponded well
with the microscopic and functional analysis of the biota present.
Guest Editor: John M. Melack
Saline Waters and their Biota 相似文献
10.
Ketil Bernt S?rensen Donald E. Canfield Andreas P. Teske Aharon Oren 《Applied microbiology》2005,71(11):7352-7365
A hypersaline, endoevaporitic microbial community in Eilat, Israel, was studied by microscopy and by PCR amplification of genes for 16S rRNA from different layers. In terms of biomass, the oxygenic layers of the community were dominated by Cyanobacteria of the Halothece, Spirulina, and Phormidium types, but cell counts (based on 4′,6′-diamidino-2-phenylindole staining) and molecular surveys (clone libraries of PCR-amplified genes for 16S rRNA) showed that oxygenic phototrophs were outnumbered by the other constituents of the community, including chemotrophs and anoxygenic phototrophs. Bacterial clone libraries were dominated by phylotypes affiliated with the Bacteroidetes group and both photo- and chemotrophic groups of α-proteobacteria. Green filaments related to the Chloroflexi were less abundant than reported from hypersaline microbial mats growing at lower salinities and were only detected in the deepest part of the anoxygenic phototrophic zone. Also detected were nonphototrophic γ- and δ-proteobacteria, Planctomycetes, the TM6 group, Firmicutes, and Spirochetes. Several of the phylotypes showed a distinct vertical distribution in the crust, suggesting specific adaptations to the presence or absence of oxygen and light. Archaea were less abundant than Bacteria, their diversity was lower, and the community was less stratified. Detected archaeal groups included organisms affiliated with the Methanosarcinales, the Halobacteriales, and uncultured groups of Euryarchaeota. 相似文献