Evidence for recycled Archaean oceanic mantle lithosphere in the Azores plume

The compositional differences between mid-ocean-ridge and ocean-island basalts place important constraints on the form of mantle convection. Also, it is thought that the scale and nature of heterogeneities within plumes and the degree to which heterogeneous material endures within the mantle might be reflected in spatial variations of basalt composition observed at the Earth's surface. Here we report osmium isotope data on lavas from a transect across the Azores archipelago which vary in a symmetrical pattern across what is thought to be a mantle plume. Many of the lavas from the centre of the plume have lower 187Os/188Os ratios than most ocean-island basalts and some extend to subchondritic 187Os/188Os ratios-lower than any yet reported from ocean-island basalts. These low ratios require derivation from a depleted, harzburgitic mantle, consistent with the low-iron signature of the Azores plume. Rhenium-depletion model ages extend to 2.5 Gyr, and we infer that the osmium isotope signature is unlikely to be derived from Iberian subcontinental lithospheric mantle. Instead, we interpret the osmium isotope signature as having a deep origin and infer that it may be recycled, Archaean oceanic mantle lithosphere that has delaminated from its overlying oceanic crust. If correct, our data provide evidence for deep mantle subduction and storage of oceanic mantle lithosphere during the Archaean era.     

Rate of molecular evolution of the seminal protein gene SEMG2 correlates with levels of female promiscuity

Postcopulatory sperm competition is a key aspect of sexual selection and is believed to drive the rapid evolution of both reproductive physiology and reproduction-related genes. It is well-established that mating behavior determines the intensity of sperm competition, with polyandry (i.e., female promiscuity) leading to fiercer sperm competition than monandry. Studies in mammals, particularly primates, showed that, owing to greater sperm competition, polyandrous taxa generally have physiological traits that make them better adapted for fertilization than monandrous species, including bigger testes, larger seminal vesicles, higher sperm counts, richer mitochondrial loading in sperm and more prominent semen coagulation. Here, we show that the degree of polyandry can also impact the dynamics of molecular evolution. Specifically, we show that the evolution of SEMG2, the gene encoding semenogelin II, a main structural component of semen coagulum, is accelerated in polyandrous primates relative to monandrous primates. Our study showcases the intimate relationship between sexual selection and the molecular evolution of reproductive genes.     

Genome sequence of Silicibacter pomeroyi reveals adaptations to the marine environment

Since the recognition of prokaryotes as essential components of the oceanic food web, bacterioplankton have been acknowledged as catalysts of most major biogeochemical processes in the sea. Studying heterotrophic bacterioplankton has been challenging, however, as most major clades have never been cultured or have only been grown to low densities in sea water. Here we describe the genome sequence of Silicibacter pomeroyi, a member of the marine Roseobacter clade (Fig. 1), the relatives of which comprise approximately 10-20% of coastal and oceanic mixed-layer bacterioplankton. This first genome sequence from any major heterotrophic clade consists of a chromosome (4,109,442 base pairs) and megaplasmid (491,611 base pairs). Genome analysis indicates that this organism relies upon a lithoheterotrophic strategy that uses inorganic compounds (carbon monoxide and sulphide) to supplement heterotrophy. Silicibacter pomeroyi also has genes advantageous for associations with plankton and suspended particles, including genes for uptake of algal-derived compounds, use of metabolites from reducing microzones, rapid growth and cell-density-dependent regulation. This bacterium has a physiology distinct from that of marine oligotrophs, adding a new strategy to the recognized repertoire for coping with a nutrient-poor ocean.     

TRPA1 is a candidate for the mechanosensitive transduction channel of vertebrate hair cells

Mechanical deflection of the sensory hair bundles of receptor cells in the inner ear causes ion channels located at the tips of the bundle to open, thereby initiating the perception of sound. Although some protein constituents of the transduction apparatus are known, the mechanically gated transduction channels have not been identified in higher vertebrates. Here, we investigate TRP (transient receptor potential) ion channels as candidates and find one, TRPA1 (also known as ANKTM1), that meets criteria for the transduction channel. The appearance of TRPA1 messenger RNA expression in hair cell epithelia coincides developmentally with the onset of mechanosensitivity. Antibodies to TRPA1 label hair bundles, especially at their tips, and tip labelling disappears when the transduction apparatus is chemically disrupted. Inhibition of TRPA1 protein expression in zebrafish and mouse inner ears inhibits receptor cell function, as assessed with electrical recording and with accumulation of a channel-permeant fluorescent dye. TRPA1 is probably a component of the transduction channel itself.     

环境生物技术的实践(英文)

环境生物技术所从事的是"使微生物群落能为人类社会提供服务",它的成功来自与原核微生物的协同作用,其广泛的代谢能力可以被利用来破坏污染物的结构并产生可再生材料.要想发挥微生物的作用,需要通过微生物分子生态学、分析化学和数学建模等学科的发展去很好地理解它,从而看清微生物黑箱模型内部的本质.同样重要的是将对生物技术的理解转化为"利用好微生物以使他们为我们工作".这种转化需要新颖的反应器设计,先进材料的利用,以及与用户的良好合作.成立于2005年的亚利桑那州立大学Swette环境生物技术中心,就是将相关的科学与工程领域中的多种方法和手段汇集在一起,形成了一种跨学科的研究中心.该中心强调团队协作精神,并与世界各地的研究者和实践者进行合作.介绍了3个新的技术:用于消减水中许多氧化性污染物的H2基膜生物膜反应器(MBfR);用于有机污染物转化为可再能源的微生物电化学电池(MXCs);以及用于加速难生物降解有机污染物脱毒的光催化与生物降解紧密结合的光-生物催化技术说明了中心是如何将基本原理应用于"利用好微生物"的.     

A diffusion mechanism for core-mantle interaction

Understanding the geochemical behaviour of the siderophile elements--those tending to form alloys with iron in natural environments--is important in the search for a deep-mantle chemical 'fingerprint' in upper mantle rocks, and also in the evaluation of models of large-scale differentiation of the Earth and terrestrial planets. These elements are highly concentrated in the core relative to the silicate mantle, but their concentrations in upper mantle rocks are higher than predicted by most core-formation models. It has been suggested that mixing of outer-core material back into the mantle following core formation may be responsible for the siderophile element ratios observed in upper mantle rocks. Such re-mixing has been attributed to an unspecified metal-silicate interaction in the reactive D' layer just above the core-mantle boundary. The siderophile elements are excellent candidates as indicators of an outer-core contribution to the mantle, but the nature and existence of possible core-mantle interactions is controversial. In light of the recent findings that grain-boundary diffusion of oxygen through a dry intergranular medium may be effective over geologically significant length scales and that grain boundaries can be primary storage sites for incompatible lithophile elements, the question arises as to whether siderophile elements might exhibit similar (or greater) grain-boundary mobility. Here we report experimental results from a study of grain-boundary diffusion of siderophile elements through polycrystalline MgO that were obtained by quantifying the extent of alloy formation between initially pure metals separated by approximately 1 mm of polycrystalline MgO. Grain-boundary diffusion resulted in significant alloying of sink and source particles, enabling calculation of grain-boundary fluxes. Our computed diffusivities were high enough to allow transport of a number of siderophile elements over geologically significant length scales (tens of kilometres) over the age of the Earth. This finding establishes grain-boundary diffusion as a potential fast pathway for chemical communication between the core and mantle.     

Methane oxidation by an extremely acidophilic bacterium of the phylum Verrucomicrobia

Aerobic methanotrophic bacteria consume methane as it diffuses away from methanogenic zones of soil and sediment. They act as a biofilter to reduce methane emissions to the atmosphere, and they are therefore targets in strategies to combat global climate change. No cultured methanotroph grows optimally below pH 5, but some environments with active methane cycles are very acidic. Here we describe an extremely acidophilic methanotroph that grows optimally at pH 2.0-2.5. Unlike the known methanotrophs, it does not belong to the phylum Proteobacteria but rather to the Verrucomicrobia, a widespread and diverse bacterial phylum that primarily comprises uncultivated species with unknown genotypes. Analysis of its draft genome detected genes encoding particulate methane monooxygenase that were homologous to genes found in methanotrophic proteobacteria. However, known genetic modules for methanol and formaldehyde oxidation were incomplete or missing, suggesting that the bacterium uses some novel methylotrophic pathways. Phylogenetic analysis of its three pmoA genes (encoding a subunit of particulate methane monooxygenase) placed them into a distinct cluster from proteobacterial homologues. This indicates an ancient divergence of Verrucomicrobia and Proteobacteria methanotrophs rather than a recent horizontal gene transfer of methanotrophic ability. The findings show that methanotrophy in the Bacteria is more taxonomically, ecologically and genetically diverse than previously thought, and that previous studies have failed to assess the full diversity of methanotrophs in acidic environments.     

LKB1 modulates lung cancer differentiation and metastasis

Germline mutation in serine/threonine kinase 11 (STK11, also called LKB1) results in Peutz-Jeghers syndrome, characterized by intestinal hamartomas and increased incidence of epithelial cancers. Although uncommon in most sporadic cancers, inactivating somatic mutations of LKB1 have been reported in primary human lung adenocarcinomas and derivative cell lines. Here we used a somatically activatable mutant Kras-driven model of mouse lung cancer to compare the role of Lkb1 to other tumour suppressors in lung cancer. Although Kras mutation cooperated with loss of p53 or Ink4a/Arf (also known as Cdkn2a) in this system, the strongest cooperation was seen with homozygous inactivation of Lkb1. Lkb1-deficient tumours demonstrated shorter latency, an expanded histological spectrum (adeno-, squamous and large-cell carcinoma) and more frequent metastasis compared to tumours lacking p53 or Ink4a/Arf. Pulmonary tumorigenesis was also accelerated by hemizygous inactivation of Lkb1. Consistent with these findings, inactivation of LKB1 was found in 34% and 19% of 144 analysed human lung adenocarcinomas and squamous cell carcinomas, respectively. Expression profiling in human lung cancer cell lines and mouse lung tumours identified a variety of metastasis-promoting genes, such as NEDD9, VEGFC and CD24, as targets of LKB1 repression in lung cancer. These studies establish LKB1 as a critical barrier to pulmonary tumorigenesis, controlling initiation, differentiation and metastasis.