Algae acquire vitamin B12 through a symbiotic relationship with bacteria

Vitamin B12 (cobalamin) was identified nearly 80 years ago as the anti-pernicious anaemia factor in liver, and its importance in human health and disease has resulted in much work on its uptake, cellular transport and utilization. Plants do not contain cobalamin because they have no cobalamin-dependent enzymes. Deficiencies are therefore common in strict vegetarians, and in the elderly, who are susceptible to an autoimmune disorder that prevents its efficient uptake. In contrast, many algae are rich in vitamin B12, with some species, such as Porphyra yezoensis (Nori), containing as much cobalamin as liver. Despite this, the role of the cofactor in algal metabolism remains unknown, as does the source of the vitamin for these organisms. A survey of 326 algal species revealed that 171 species require exogenous vitamin B12 for growth, implying that more than half of the algal kingdom are cobalamin auxotrophs. Here we show that the role of vitamin B12 in algal metabolism is primarily as a cofactor for vitamin B12-dependent methionine synthase, and that cobalamin auxotrophy has arisen numerous times throughout evolution, probably owing to the loss of the vitamin B12-independent form of the enzyme. The source of cobalamin seems to be bacteria, indicating an important and unsuspected symbiosis.     

基于分级遗传算法的结构损伤识别方法

提出了一种基于遗传算法的利用不完整振动数据识别结构损伤的新方法，该方法首先扩展不完整的振型并利用单元能量熵差比确定结构损伤的大致位置，然后采用二级搜索策略，借助遗传算法确定结构损伤的程度，数值计算结果表明，当可能的损伤区域较大时，本方法较直接搜索策略更能有效地确定结构损伤的程度。     

Inactivation of the apoptosis effector Apaf-1 in malignant melanoma

Metastatic melanoma is a deadly cancer that fails to respond to conventional chemotherapy and is poorly understood at the molecular level. p53 mutations often occur in aggressive and chemoresistant cancers but are rarely observed in melanoma. Here we show that metastatic melanomas often lose Apaf-1, a cell-death effector that acts with cytochrome c and caspase-9 to mediate p53-dependent apoptosis. Loss of Apaf-1 expression is accompanied by allelic loss in metastatic melanomas, but can be recovered in melanoma cell lines by treatment with the methylation inhibitor 5-aza-2'-deoxycytidine (5aza2dC). Apaf-1-negative melanomas are invariably chemoresistant and are unable to execute a typical apoptotic programme in response to p53 activation. Restoring physiological levels of Apaf-1 through gene transfer or 5aza2dC treatment markedly enhances chemosensitivity and rescues the apoptotic defects associated with Apaf-1 loss. We conclude that Apaf-1 is inactivated in metastatic melanomas, which leads to defects in the execution of apoptotic cell death. Apaf-1 loss may contribute to the low frequency of p53 mutations observed in this highly chemoresistant tumour type.     

Sirtuin activators mimic caloric restriction and delay ageing in metazoans

Caloric restriction extends lifespan in numerous species. In the budding yeast Saccharomyces cerevisiae this effect requires Sir2 (ref. 1), a member of the sirtuin family of NAD+-dependent deacetylases. Sirtuin activating compounds (STACs) can promote the survival of human cells and extend the replicative lifespan of yeast. Here we show that resveratrol and other STACs activate sirtuins from Caenorhabditis elegans and Drosophila melanogaster, and extend the lifespan of these animals without reducing fecundity. Lifespan extension is dependent on functional Sir2, and is not observed when nutrients are restricted. Together these data indicate that STACs slow metazoan ageing by mechanisms that may be related to caloric restriction.     

A general model for ontogenetic growth.

Several equations have been proposed to describe ontogenetic growth trajectories for organisms justified primarily on the goodness of fit rather than on any biological mechanism. Here, we derive a general quantitative model based on fundamental principles for the allocation of metabolic energy between maintenance of existing tissue and the production of new biomass. We thus predict the parameters governing growth curves from basic cellular properties and derive a single parameterless universal curve that describes the growth of many diverse species. The model provides the basis for deriving allometric relationships for growth rates and the timing of life history events.     

Direct detection of more than 50% of the Duchenne muscular dystrophy mutations by field inversion gels

Duchenne muscular dystrophy (DMD) is an X-linked disorder affecting about 1 in 3,500 males. It is allelic with the milder Becker muscular dystrophy. The biochemical basis for both diseases is unknown and no effective treatment is available. Long-range physical mapping has shown that the DMD gene, localized in Xp21, is extremely large, exceeding 2 million base pairs. Until now, carrier detection and prenatal diagnosis has involved the use of linked restriction fragment length polymorphism markers which detect muscular dystrophy-associated deletions in about 10% of the cases. Field inversion gel electrophoresis (FIGE) allows the detection of structural rearrangements in 21 out of 39 of the DMD patients studied (54%), of which 14 (65%) were not detected by conventional methods. Large deletions seem to make up a much higher fraction of the DMD mutations than so far indicated by other methods. A region prone to deletion was located in the distal half of the gene. FIGE analysis could provide a valuable extension of information for carrier detection and prenatal diagnosis. The technique should be generally applicable to the study of diseases involving structural chromosomal rearrangements.     

Nanostructured TiO2（B）:the effect of size and shape on anode properties for Li-ion batteries

Reducing the dimensions of electrode materials from the micron to the nanoscale can have a profound influence on their properties and hence on the performance of electrochemical devices,e.g.Li-ion batteries,that employ such electrodes.TiO2(B) has received growing interest as a possible anode for Li-ion batteries in recent years.It offers the possibility of higher energy storage compared with the commercialized Li4Ti5O12.Bulk,nanowire,nanotube,and nanoparticle morphologies have been prepared and studied.However,to date these materials have not be compared in one article.In the current review we first summarize the different synthesis methods for the preparation of nanostructured TiO2(B);then present the effects of size and shape on the electrochemical properties.Finally TiO2(B) with nanometer dimensions exhibit a higher capacity to store Li,regardless of rate,due to structural distortions inherent at the nanoscale.     

十次幂和问题的解

给出不定方程１０＝ ｙ１０的一组正整数解     

Soil fertility limits carbon sequestration by forest ecosystems in a CO2-enriched atmosphere

Northern mid-latitude forests are a large terrestrial carbon sink. Ignoring nutrient limitations, large increases in carbon sequestration from carbon dioxide (CO2) fertilization are expected in these forests. Yet, forests are usually relegated to sites of moderate to poor fertility, where tree growth is often limited by nutrient supply, in particular nitrogen. Here we present evidence that estimates of increases in carbon sequestration of forests, which is expected to partially compensate for increasing CO2 in the atmosphere, are unduly optimistic. In two forest experiments on maturing pines exposed to elevated atmospheric CO2, the CO2-induced biomass carbon increment without added nutrients was undetectable at a nutritionally poor site, and the stimulation at a nutritionally moderate site was transient, stabilizing at a marginal gain after three years. However, a large synergistic gain from higher CO2 and nutrients was detected with nutrients added. This gain was even larger at the poor site (threefold higher than the expected additive effect) than at the moderate site (twofold higher). Thus, fertility can restrain the response of wood carbon sequestration to increased atmospheric CO2. Assessment of future carbon sequestration should consider the limitations imposed by soil fertility, as well as interactions with nitrogen deposition.     

Size-dependent optical properties of Au nanorods

In the fast evolving field of nanoscience and nanotechnology,where size and shape are crucial in deciding the optoelectronic properties of nanomaterials,the understanding of size and shape dependent behavior is of direct relevance to device applications.Present study reports the synthesis of Au nanorods with well controlled aspect ratios,and the influence of the aspect ratio on the surface enhanced Raman scattering(SERS) activity using crystal violet(CV) as the probe molecule.The influence of pH and the concentrations of reducing agent and Ag ions in controlling the aspect ratio of gold nanorods are also investigated.The structural and optical properties of the synthesized samples have been characterized by transmission electron microscopy(TEM) and UV-visible absorption spectroscopy.The nonlinear optical(NLO) transmission of the Au nanorods investigated using the open aperture Z-scan technique revealed the absorption saturation followed by an optical limiting behavior,which may find potential applications in optoelectronic nanodevices.