Variety Of Organisms (variety + of_organism)

Distribution by Scientific Domains

Selected Abstracts

Body size determines the strength of the latitudinal diversity gradient

ECOGRAPHY, Issue 3 2001
Helmut Hillebrand
In most groups of organisms, the species richness decreases from the tropics to the poles. The mechanisms causing this latitudinal diversity gradient are still controversial. We present data from a comprehensive weighted meta-analysis on the strength of the latitudinal gradient in relation to body size. We sampled literature data on the correlation between species richness and latitude for a variety of organisms, ranging from trees to protozoa. In addition, own data on the presence of large-scale diversity patterns for diatoms were included, both for local and regional species richness. The strength of the latitudinal gradient was positively correlated to the size of the organisms. Strongest decreases of species richness to the poles was found for large organisms like trees and vertebrates, whereas meiofauna, protozoa and diatoms showed weak or no correlations between species richness and latitude. These results imply that latitudinal gradients are shaped by non-equilibrium (regional) processes and are persistent under conditions of dispersal limitation. [source]

Antimicrobial therapy for multidrug resistant pathogens

J. S. Weese
Summary Multidrug resistant bacteria are tremendous causes of morbidity and mortality in human medicine, and emerging pathogens in equine medicine. A variety of organisms, such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin resistant Enterococcus spp. (VRE) and multidrug resistant Acinetobacter spp., Pseudomonas spp. and Enterobacteriaceae are of concern in equine medicine. Veterinary practitioners need to be aware of key diagnostic, clinical, therapeutic, epidemiological and infection control aspects to limit the impact of these organisms on the equine, and perhaps human, population. [source]

Origins and significance of ergot alkaloid diversity in fungi

Daniel G. Panaccione
Abstract Ergot alkaloids are a diverse family of indole-derived mycotoxins that collectively have activities against a variety of organisms including bacteria, nematodes, insects, and mammals. Different fungi accumulate different, often characteristic, profiles of ergot alkaloids rather than a single pathway end product. These ergot alkaloid profiles result from inefficiency in the pathway leading to accumulation of certain intermediates or diversion of intermediates into shunts along the pathway. The inefficiency generating these ergot alkaloid profiles may have been selected for as a means of accumulating a diversity of ergot alkaloids, potentially contributing in different ways to benefit the producing fungus. [source]

Resource competition and plant traits: a response to Craine et al.


Summary 1Resource competition theory incorporates the mechanisms that underlie consumer,resource interactions and the trade-offs that constrain these mechanisms. Contrary to assertions by Craine, the concept of R* as the measure of resource reduction and the predictor of resource competition has not changed since it was proposed more than two decades ago. 2Resource reduction, as summarized in R*, is readily observed. Soil concentrations of nitrate and water are decreased by plant uptake, and are lowered to different levels by different species. Tests have shown R* theory to correctly predict competitive outcomes for a variety of organisms and ecosystems. 3Consumer-resource mechanisms are a building block for theories that incorporate other trade-offs faced by plants, such as those between competitive ability and dispersal. 4Numerous plant traits interactively determine R* in a manner predictable from trait-based resource competition theory. The same traits shown by comparative research to be associated with plant dominance in low-nutrient habitats give lower R* values, greater predicted competitive ability and greater predicted abundances in nutrient-limited habitats. 5Plant ecology needs closer links between analytical theory, observations and experiments. Simple verbal theories can generate novel ideas but the logical implications of such scenarios are best explored using the rigorous logic of mathematics. Predictions of theory can then be tested via experiments and comparative studies. [source]

Ambient temperature influences aging in an annual fish (Nothobranchius rachovii)

AGING CELL, Issue 6 2009
Chin-Yuan Hsu
Summary Extending lifespan by lowering ambient temperature in the habitat has been shown in a variety of organisms. Its mechanism, however, remains elusive. In this study, we examined the survivorship and the aging process of the annual fish (Nothobranchius rachovii) reared under high (30 ░C), moderate (25 ░C) and low (20 ░C) ambient temperatures. The results showed that low ambient temperatures prolong survivorship, whereas high ambient temperatures shorten survivorship. At low ambient temperature, expression of senescence-associated ,-galactosidase, lipofuscin, reactive oxygen species, lipid peroxidation, protein oxidation, mitochondrial density and ADP/ATP ratio were reduced compared with those reared at high and moderate temperatures, whereas catalase activity, Mn-superoxide dismutase activities, mitochondrial membrane potential and the levels of ATP, ADP, Sirt1 and Forkhead box O expression were elevated. The expression levels of Hsp70 and CIRP showed no significant difference under any of the ambient temperatures tested. We concluded that cellular metabolism, energy utilization and gene expression are altered at lower ambient temperature, which is associated with the extension of lifespan of the annual fish. [source]

Speciation, hybrid zones and phylogeography , or seeing genes in space and time

Godfrey M. Hewitt
Abstract The origins and development of the study of speciation, hybrid zones and phylogeography are outlined using evolutionary iconography. This traces the ideas in this field from Lamarck and Darwin through to the present as represented in diagrams and figures. A ,tree of trees' summarizes this growth and current vitality. The new facility to use various DNA sequences from nuclear, mitochondrial and chloroplast genomes to determine genetic variation throughout a species range is examined particularly. There is great genomic subdivision across species distributions, which can be interpreted in the light of the recent demonstrations of severe palaeoclimatic oscillations. Refugia and postglacial colonization routes are proposed for several organisms across Europe. The role of geography in speciation through the Pleistocene is considered. These emerging principles and analyses are applied to data available on a variety of organisms in other regions of the world, such as the Arctic, North America and the Tropics, and including the progress of Homo sapiens through the last ice age. Some suggestions are made for future research directions. [source]

Multiple transporters associated with malaria parasite responses to chloroquine and quinine

Jianbing Mu
Summary Mutations and/or overexpression of various transporters are known to confer drug resistance in a variety of organisms. In the malaria parasite Plasmodium falciparum, a homologue of P-glycoprotein, PfMDR1, has been implicated in responses to chloroquine (CQ), quinine (QN) and other drugs, and a putative transporter, PfCRT, was recently demonstrated to be the key molecule in CQ resistance. However, other unknown molecules are probably involved, as different parasite clones carrying the same pfcrt and pfmdr1 alleles show a wide range of quantitative responses to CQ and QN. Such molecules may contribute to increasing incidences of QN treatment failure, the molecular basis of which is not understood. To identify additional genes involved in parasite CQ and QN responses, we assayed the in vitro susceptibilities of 97 culture-adapted cloned isolates to CQ and QN and searched for single nucleotide polymorphisms (SNPs) in DNA encoding 49 putative transporters (total 113 kb) and in 39 housekeeping genes that acted as negative controls. SNPs in 11 of the putative transporter genes, including pfcrt and pfmdr1, showed significant associations with decreased sensitivity to CQ and/or QN in P. falciparum. Significant linkage disequilibria within and between these genes were also detected, suggesting interactions among the transporter genes. This study provides specific leads for better understanding of complex drug resistances in malaria parasites. [source]

Double-stranded RNA-mediated gene silencing of cysteine proteases (falcipain-1 and -2) of Plasmodium falciparum

Pawan Malhotra
Summary Malaria remains a public health problem of enormous magnitude, affecting over 500 million people every year. Lack of success in the past in the development of new drug/vaccines has mainly been attributed to poor understanding of the functions of different parasite proteins. Recently, RNA interference (RNAi) has emerged as a simple and incisive technique to study gene functions in a variety of organisms. In this study, we report the results of RNAi by double-stranded RNA of cysteine protease genes (falcipain -1 and -2) in the malaria parasite, Plasmodium falciparum. Using RNAi directed towards falcipain genes, we demonstrate that blocking the expression of these genes results in severe morphological abnormalities in parasites, inhibition of parasite growth in vitro and substantial şaccumulation of haemoglobin in the parasite. The inhibitory effects produced by falcipain double-stranded (ds)RNAs are reminiscent of the effects observed upon administering E-64, a cysteine protease inhibitor. The parasites treated with falcipain's dsRNAs also show marked reduction in the levels of corresponding endogenous falcipain mRNAs. We also demonstrate that dsRNAs of falcipains are şbroken into short interference RNAs , 25 nucleotides in size, a characteristic of RNAi, which in turn activates sequence-specific nuclease activity in the malaria parasites. These results thus provide more evidence for the existence of RNAi in P. falciparum and also suggest possibilities for using RNAi as an effective tool to determine the functions of the genes identified from the P. falciparum genome sequencing project. [source]

Comparison of the sequences of the Aspergillus nidulans hxB and Drosophila melanogaster ma-l genes with nifS from Azotobacter vinelandii suggests a mechanism for the insertion of the terminal sulphur atom in the molybdopterin cofactor

La´la Amrani
The molybdopterin cofactor (MoCF) is required for the activity of a variety of oxidoreductases. The xanthine oxidase class of molybdoenzymes requires the MoCF to have a terminal, cyanolysable sulphur ligand. In the sulphite oxidase/nitrate reductase class, an oxygen is present in the same position. Mutations in both the ma-l gene of Drosophila melanogaster and the hxB gene of Aspergillus nidulans result in loss of activities of all molybdoenzymes that necessitate a cyanolysable sulphur in the active centre. The ma-l and hxB genes encode highly similar proteins containing domains common to pyridoxal phosphate-dependent cysteine transulphurases, including the cofactor binding site and a conserved cysteine, which is the putative sulphur donor. Key similarities were found with NifS, the enzyme involved in the generation of the iron,sulphur centres in nitrogenase. These similarities suggest an analogous mechanism for the generation of the terminal molybdenum-bound sulphur ligand. We have identified putative homologues of these genes in a variety of organisms, including humans. The human homologue is located in chromosome 18.q12. [source]

Genomic mutation rates: what high-throughput methods can tell us

BIOESSAYS, Issue 9 2009
Koodali T. Nishant
Abstract High-throughput DNA analyses are increasingly being used to detect rare mutations in moderately sized genomes. These methods have yielded genome mutation rates that are markedly higher than those obtained using pre-genomic strategies. Recent work in a variety of organisms has shown that mutation rate is strongly affected by sequence context and genome position. These observations suggest that high-throughput DNA analyses will ultimately allow researchers to identify trans -acting factors and cis sequences that underlie mutation rate variation. Such work should provide insights on how mutation rate variability can impact genome organization and disease progression. [source]

Purification, crystallization and preliminary structural analysis of nucleoside diphosphate kinase from Bacillus anthracis

Gauri Misra
Bacillus anthracis nucleoside diphosphate kinase (BaNdk) is an enzyme whose primary function is to maintain deoxynucleotide triphosphate (dNTP) pools by converting deoxynucleotide diphosphates to triphosphates using ATP as the major phosphate donor. Although the structures of Ndks from a variety of organisms have been elucidated, the enzyme from sporulating bacteria has not been structurally characterized to date. Crystals of the B. anthracis enzyme were grown using the vapour-diffusion method from a hanging drop consisting of 2,Ál 10,mg,ml,1 protein in 50,mM Tris,HCl pH 8.0, 50,mM NaCl, 5,mM EDTA equilibrated against 500,Ál reservoir solution consisting of 2.25,M ammonium formate and 0.1,M HEPES buffer pH 7.25. Diffraction data extending to 2.0,┼ were collected at room temperature from a single crystal with unit-cell parameters a = b = 107.53, c = 52.3,┼. The crystals are hexagonal in shape and belong to space group P6322. The crystals contain a monomer in the asymmetric unit, which corresponds to a Matthews coefficient (VM) of 2.1,┼3,Da,1 and a solvent content of about 36.9%. [source]

RNA interference in protozoan parasites

Elisabetta Ullu
Summary RNA interference or RNAi is defined as the mechanism through which gene-specific, double-stranded RNA (dsRNA) triggers degradation of homologous transcripts. Besides providing an invaluable tool to downregulate gene expression in a variety of organisms, it is now evident that RNAi extends its tentacles into both the nucleus and the cytoplasm and is involved in a variety of gene silencing phenomena. Here we review the current status of RNAi in protozoan parasites that cause diseases of considerable medical and veterinary importance throughout Africa, Asia and the Americas. RNAi was first discovered in Trypanosoma brucei, a species of the family Trypanosomatidae, and it rapidly became the method of choice to downregulate gene expression in these organisms. At the same time, mechanistic studies exposed a role for RNAi in the control of retroposon transcript abundance. Whereas RNAi is also present in T. congolense, other members of the same family of organisms, namely T. cruzi and Leishmania major, are RNAi-negative. In apicomplexan parasites, there is experimental evidence for RNAi in Plasmodium, but this is not supported by their genetic make up. In contrast, the genome of Toxoplasma gondii harbours gene candidates with convincing similarity to ,classical' RNAi genes. Thus, as previously shown in fungi, protozoan parasites are genetically heterogeneous as far as the RNAi pathway is concerned. Finally, database mining predicts that Entamoeba histolytica and Giardia intestinalis have an RNAi pathway and the presence of RNAi genes in Giardia supports the view that gene silencing by dsRNA appeared very early during evolution of the eukaryotic lineage. [source]