静磁场对单株人体体表正常菌生长影响的研究

本文通过40mT和120mT两种静磁场作用下表皮葡萄球菌生长过程的研究,发现试验所选强度静磁场加速了表皮葡萄球菌在对数生长期的生长速率,而在进入稳定生长期后其生长速率反而低于对照组,但就整个生长周期而言,静磁场作用下表皮葡萄球菌的总量大于对照组,表明了试验所选静磁场对表皮葡萄球菌生长有一定促进作用.     

Distinctive repertoire of contingency genes conferring mutation- based phase variation and combinatorial expression of surface lipoproteins in Mycoplasma capricolum subsp. capricolum of the Mycoplasma mycoides phylogenetic cluster

The generation of surface variation among many divergent species of Mollicutes (mycoplasmas) occurs through stochastic expression patterns of diverse lipoprotein genes. The size and wide distribution of such variable gene sets in minimal (approximately 0.6- to 1.4-Mb) mycoplasmal genomes suggest their key role in the adaptation and survival of these wall-less monoderms. Diversity through variable genes is less clearly established among phylogenetically similar mycoplasmas, such as the Mycoplasma mycoides cluster of ruminant pathogens, which vary widely in host range and pathobiology. Using (i) genome sequences from two members of this clade, Mycoplasma capricolum subsp. capricolum and M. mycoides subsp. mycoides small colony biotype (SC), (ii) antibodies to specific peptide determinants of predicted M. capricolum subsp. capricolum gene products, and (iii) analysis of the membrane-associated proteome of M. capricolum subsp. capricolum, a novel set of six genes (vmcA to vmcF) expressing distinct Vmc (variable M. capricolum subsp. capricolum) lipoproteins is demonstrated. These occur at two separate loci in the M. capricolum subsp. capricolum genome, which shares striking overall similarity and gene synteny with the M. mycoides subsp. mycoides SC genome. Collectively, Vmc expression is noncoordinate and combinatorial, subject to a single-unit insertion/deletion in a 5' flanking dinucleotide repeat that governs expression of each vmc gene. All vmc genes share modular regions affecting expression and membrane translocation. In contrast, vmcA to vmcD genes at one locus express surface proteins with highly structured size-variable repeating domains, whereas vmcE to vmcF genes express products with short repeats devoid of predicted structure. These genes confer a distinctive, dynamic surface architecture that may represent adaptive differences within this important group of pathogens as well as exploitable diagnostic targets.     

Prediction of nucleating sequences from amyloidogenic propensities of tau-related peptides

Physical properties, including amyloid morphology, FTIR and CD spectra, enhancement of Congo red absorbance, polymerization rate, critical monomer concentration, free energy of stabilization, hydrophobicity, and the partition coefficient between soluble and amyloid states, were measured for the tau-related peptide Ac-VQIVYK amide (AcPHF6) and its single site mutants Ac-VQIVXK amide (X not equal Cys). Transmission electron microscopy showed that 15 out of the 19 peptides formed amyloid in buffer, with morphologies ranging from straight and twisted filaments to sheets and rolled sheets. Using principal component analysis (PCA), measured properties were treated in a comprehensive manner, and scores along the most significant principal components were used to define individual amino acid amyloidogenic propensities. Quantitative structure-activity modeling (QSAM) showed that residues with greater size and hydrophobicity made the largest contributions to the propensity of peptides to form amyloid. Using individual amino acid propensities, sequences within tau with high amyloid-forming potential were estimated and found to include 226VAVVR230 in the proline-rich region, 275VQIINK280 (PHF6) and 306VQIVYK311 (PHF6) within the microtubule binding region, and 392IVYK395 in the C-tail region of the protein. The results suggest that regions outside the microtubule-binding region may play important roles in tau aggregation kinetics or paired helical filament structure.     

Rapid, reversible alterations in spinach thylakoid appression upon changes in light intensity

Changes in light quantity and quality cause structural changes within the thylakoid membrane; long‐term responses have been described for so‐called ‘sun’ and ‘shade’ leaves. Many leaves, however, experience changes in irradiance on a time scale of minutes due to self‐shading and sun flecks. In this study, mature, attached spinach leaves were grown at 300 µmol photons m^?2 s^?1 then rapidly switched to a different light treatment. The treatment irradiances were 10, 800 or 1500 µmol m^?2 s^?1 for 10 min, or 10 or 20 min of self‐shading (about 10 µmol m^?2 s^?1). Image analysis of transmission electron micrographs revealed that a 10 min switch to a lower light intensity increased grana size and number per chloroplast profile by 10–20%. Returning the leaves to 300 µmol m^?2 s^?1 for 10 min reversed the phenomenon. Chlorophyll fluorescence measurements of detached, intact leaves at 77 K were suggestive of a transition from state 2 to state 1 upon shading. Diurnal ultrastructural measurements of granal size and number did not reveal a significant net change in ultrastructure over the time scale of hours. It is concluded that spinach chloroplasts can alter the degree of thylakoid appression in response to irradiance changes on a time scale of minutes. These ultrastructural responses are caused by biochemical and biophysical adjustments within the thylakoid membrane that serve to maximize photosynthesis and minimize photo‐inhibition under rapidly fluctuating light environments.     

Growth, development, and survival of a generalist predator fed single- and mixed-species diets of different quality

It is often assumed that prey species consumed by generalist predators are largely, though not entirely, equivalent in terms of their value to the predators. In contrast to this expectation, laboratory feeding experiments uncovered distinctly varied developmental responses of a generalist predator, the wolf spider Schizocosa, to different experimental diets. Naive Schizocosa attacked and fed upon all the prey species offered; however, highly divergent patterns of survival, development, and growth of Schizocosa spiderlings reared on different single-prey diets revealed a wide spectrum of prey qualities. Spiderlings fed the collembolan Tomocerus bidentatus sustained the highest overall rates of survival, growth, and development. Fruit flies (Drosophila melanogaster) were intermediate-quality prey: spiders fed Drosophila initially exhibited rates of survival, growth, and development equal to those of spiders on a diet of T. bidentatus, but after about 3 months, rates declined markedly. Fungus gnats (Sciaridae; Bradysia sp.) and conspecfic spiderlings are low-quality prey for Schizocosa: a sole diet of either of these prey types resulted in positive but markedly submaximal rates of growth, retarded rates of development, and survival rates much lower than that supported by a diet of Drosophila. Worst were the collembolans Folsomia candida and Isotoma trispinata, and the aphid Aphis nerii: spiderlings fed solely one of these species did not grow and died without molting. A. nerii is classified as poor quality because survival was no better than that of starved controls. F. candida and I. trispinata were toxic: survival of Schizocosa hatchlings fed these collembolans was lower than that of starved controls. A mixed diet of T. bidentatus and fruit flies yielded positive synergistic effects with respect to growth, but development and rate of survival were similar to those of spiders on a sole diet of T. bidentatus. Including toxic prey did not produce a better diet, while inclusion of toxic prey with prey of higher quality created diets that were no better than the toxic prey alone. The results of these experiments suggest that prey species that are similar in morphology and behavior, and that are initially killed and consumed, may differ dramatically in their suitability as food for generalist arthropod predators. Received: 29 July 1998 / Accepted: 1 February 1999     

Heroin reward is dependent on a dopaminergic substrate

The rewarding property of heroin was blocked by pretreatment with either naloxone or pimozide, suggesting that this opiate-receptor mediated effect is dependent on a dopaminergic substrate. The involvement of a dopaminergic mechanism in this effect supports the notion that opiates and other sources of reward activate a similar neural substrate.