Endosymbiotic sulphate-reducing and sulphide-oxidizing bacteria in an oligochaete worm

Stable associations of more than one species of symbiont within a single host cell or tissue are assumed to be rare in metazoans because competition for space and resources between symbionts can be detrimental to the host. In animals with multiple endosymbionts, such as mussels from deep-sea hydrothermal vents and reef-building corals, the costs of competition between the symbionts are outweighed by the ecological and physiological flexibility gained by the hosts. A further option for the coexistence of multiple symbionts within a host is if these benefit directly from one another, but such symbioses have not been previously described. Here we show that in the gutless marine oligochaete Olavius algarvensis, endosymbiotic sulphate-reducing bacteria produce sulphide that can serve as an energy source for sulphide-oxidizing symbionts of the host. Thus, these symbionts do not compete for resources but rather share a mutalistic relationship with each other in an endosymbiotic sulphur cycle, in addition to their symbiotic relationship with the oligochaete host.     

胃肠道微生物区系在宿主体内共生作用的研究进展

宿主与肠道微生物区系长期共同进化的结果是宿主与细菌间的互利共生.在人的消化系统中拥有成千上万的共生细菌,这些共生细菌对宿主肠道的营养加工、粘膜免疫耐受和一些其它功能具有重要的作用.现行的分子生物学技术和无菌动物模型为研究宿主与共生细菌之间的分子机制提供了前所未有的机遇,有助于我们更深入地理解肠道的共生细菌对人正常生理功能的作用,从而发展新的治疗策略.     

Sulphide mining by the superextensile foot of symbiotic thyasirid bivalves

In a symbiotic association between an invertebrate host and chemoautotrophic bacteria, each partner has different metabolic requirements, and the host typically supplies the bacteria with necessary reduced chemicals (sulphide or methane). Some combination of anatomical, physiological and behavioural adaptations in the host often facilitates uptake and transport of reduced chemicals to the symbionts. We have studied five species of bivalve molluscs of the family Thyasiridae (that is, thyasirids) three of which harbour chemoautotrophic bacteria. Here we show that the symbiotic bivalves extend their feet to form elongated and ramifying burrows in the sediment, most probably to gain access to reduced sulphur. Closely related bivalves (including some thyasirid species) without bacterial symbionts show no comparable foot extension behaviour. The length and number of burrows formed by chemosymbiotic thyasirids are related to the concentration of hydrogen sulphide in the sediment. The burrows are formed by the foot of each bivalve, which can extend up to 30 times the length of the shell, and may be the most extreme case of animal structure elongation documented to date.     

植食性昆虫、植物和共生微生物的功能关联

植食性昆虫和植物均能与微生物形成密切关系，它们各自的生态功能及相互关系也常被共生微生物所影响。近年来，随着分子水平研究方法的进展，植食性昆虫和植物中很多可遗传共生微生物（细菌、真菌等）被发现。共生微生物能够在营养、生殖、防御和解毒等方面给宿主带来显著影响，并与宿主形成竞争、互利或寄生等关系。植食性昆虫体内的含菌胞、肠道、血淋巴、唾液腺等常含有重要功能的共生微生物。新的分子生物学手段和高通量测序技术的应用使得我们能够增加对宿主和共生微生物（即使处于低丰度）之间关系的了解。本文尝试总结了植食性昆虫和植物共生微生物的多样性及其关系、昆虫和植物互作机制、昆虫共生菌解毒植物毒素等方面的近期证据，突出强调了应以系统观思维来理解共生微生物、植食性昆虫和植物间的功能关联，并就将来值得研究的问题提出了建议。     

一种随机-无标度混合的P2P蠕虫传播模型

针对现有模型中只用节点度来构建蠕虫网络的不足,文中结合无标度网络性质和实际P2P网络通信的特点,引入一个表示新节点连接概率的调节参数,在此基础上以随机选择与优先依附混合的方式建立蠕虫传播模型,并利用平均场理论和Matlab仿真对模型的演化机理进行研究.理论分析与仿真实验表明:选择蠕虫网络中合适的节点和新感染蠕虫主机建立的连接与连接概率、节点吸引力等因素有着紧密的联系;所建立的蠕虫网络具有无标度网络的性质.     

Hydrogen is an energy source for hydrothermal vent symbioses

The discovery of deep-sea hydrothermal vents in 1977 revolutionized our understanding of the energy sources that fuel primary productivity on Earth. Hydrothermal vent ecosystems are dominated by animals that live in symbiosis with chemosynthetic bacteria. So far, only two energy sources have been shown to power chemosynthetic symbioses: reduced sulphur compounds and methane. Using metagenome sequencing, single-gene fluorescence in situ hybridization, immunohistochemistry, shipboard incubations and in situ mass spectrometry, we show here that the symbionts of the hydrothermal vent mussel Bathymodiolus from the Mid-Atlantic Ridge use hydrogen to power primary production. In addition, we show that the symbionts of Bathymodiolus mussels from Pacific vents have hupL, the key gene for hydrogen oxidation. Furthermore, the symbionts of other vent animals such as the tubeworm Riftia pachyptila and the shrimp Rimicaris exoculata also have hupL. We propose that the ability to use hydrogen as an energy source is widespread in hydrothermal vent symbioses, particularly at sites where hydrogen is abundant.     

Horizontal endosymbiont transmission in hydrothermal vent tubeworms

Transmission of obligate bacterial symbionts between generations is vital for the survival of the host. Although the larvae of certain hydrothermal vent tubeworms (Vestimentifera, Siboglinidae) are symbiont-free and possess a transient digestive system, these structures are lost during development, resulting in adult animals that are nutritionally dependent on their bacterial symbionts. Thus, each generation of tubeworms must be newly colonized with its specific symbiont. Here we present a model for tubeworm symbiont acquisition and the development of the symbiont-housing organ, the trophosome. Our data indicate that the bacterial symbionts colonize the developing tube of the settled larvae and enter the host through the skin, a process that continues through the early juvenile stages during which the trophosome is established from mesodermal tissue. In later juvenile stages we observed massive apoptosis of host epidermis, muscles and undifferentiated mesodermal tissue, which was coincident with the cessation of the colonization process. Characterizing the symbiont transmission process in this finely tuned mutualistic symbiosis provides another model of symbiont acquisition and additional insights into underlying mechanisms common to both pathogenic infections and beneficial host-symbiont interactions.     

灰飞虱Wolbachia群体生物学的遗传特性研究

Ｗｏｌｂａｃｈｉａ是存在于多种昆虫生殖器官的一类共生菌,它可能在宿 主群体中引起细菌质不亲和性而给宿 主带来生殖优势。对灰飞虱体内的Ｗｏｌｂａｃｈｉａｆｊｔｆｄｇｐｗ,ｖ ｇｍ ｐｇｃｆｍｗ ｑｎｎｋｕｄｙｊｒ ｄｏ ｎｕｉ     

A candidate NAD+ transporter in an intracellular bacterial symbiont related to Chlamydiae

Bacteria living within eukaryotic cells can be essential for the survival or reproduction of the host but in other cases are among the most successful pathogens. Environmental Chlamydiae, including strain UWE25, thrive as obligate intracellular symbionts within protozoa; are recently discovered relatives of major bacterial pathogens of humans; and also infect human cells. Genome analysis of UWE25 predicted that this symbiont is unable to synthesize the universal electron carrier nicotinamide adenine dinucleotide (NAD+). Compensation of limited biosynthetic capacity in intracellular bacteria is usually achieved by import of primary metabolites. Here, we report the identification of a candidate transporter protein from UWE25 that is highly specific for import of NAD+ when synthesized heterologously in Escherichia coli. The discovery of this candidate NAD+/ADP exchanger demonstrates that intact NAD+ molecules can be transported through cytoplasmic membranes. This protein acts together with a newly discovered nucleotide transporter and an ATP/ADP translocase, and allows UWE25 to exploit its host cell by means of a sophisticated metabolic parasitism.     

Evolution of a bacteria/plasmid association

Associations between bacteria and their accessory elements (viruses, plasmids and transposons) range from antagonistic to mutualistic. A number of previous studies have demonstrated that plasmid carriage reduces bacterial fitness in the absence of selection for specific functions such as antibiotic resistance. Many studies have demonstrated increased fitness of evolving microbial populations in laboratory environments, but we are aware of only one study in which fitness gains were partitioned between a plasmid and its host. Here, we examine the evolution of an association between a plasmid and its bacterial host. Carriage of the non-conjugative plasmid pACYC184 initially reduced the fitness of Escherichia coli B in the absence of antibiotic. We then cultured plasmid-bearing bacteria for 500 generations in the presence of antibiotic. The fitness of each combination of host and plasmid, with and without the culture history, was determined by competing it against a baseline strain. The results indicate adaptation by the host genome, but no plasmid adaptation. We also competed the evolved host, transformed with the baseline plasmid, against its isogenic plasmid-free counterpart. The plasmid now increased the fitness of its host.     

Revealing structure and assembly cues for Arabidopsis root-inhabiting bacterial microbiota

The plant root defines the interface between a multicellular eukaryote and soil, one of the richest microbial ecosystems on Earth. Notably, soil bacteria are able to multiply inside roots as benign endophytes and modulate plant growth and development, with implications ranging from enhanced crop productivity to phytoremediation. Endophytic colonization represents an apparent paradox of plant innate immunity because plant cells can detect an array of microbe-associated molecular patterns (also known as MAMPs) to initiate immune responses to terminate microbial multiplication. Several studies attempted to describe the structure of bacterial root endophytes; however, different sampling protocols and low-resolution profiling methods make it difficult to infer general principles. Here we describe methodology to characterize and compare soil- and root-inhabiting bacterial communities, which reveals not only a function for metabolically active plant cells but also for inert cell-wall features in the selection of soil bacteria for host colonization. We show that the roots of Arabidopsis thaliana, grown in different natural soils under controlled environmental conditions, are preferentially colonized by Proteobacteria, Bacteroidetes and Actinobacteria, and each bacterial phylum is represented by a dominating class or family. Soil type defines the composition of root-inhabiting bacterial communities and host genotype determines their ribotype profiles to a limited extent. The identification of soil-type-specific members within the root-inhabiting assemblies supports our conclusion that these represent soil-derived root endophytes. Surprisingly, plant cell-wall features of other tested plant species seem to provide a sufficient cue for the assembly of approximately 40% of the Arabidopsis bacterial root-inhabiting microbiota, with a bias for Betaproteobacteria. Thus, this root sub-community may not be Arabidopsis-specific but saprophytic bacteria that would naturally be found on any plant root or plant debris in the tested soils. By contrast, colonization of Arabidopsis roots by members of the Actinobacteria depends on other cues from metabolically active host cells.     

Neutrophil elastase targets virulence factors of enterobacteria

Shigellae cause bacillary dysentery, a bloody form of diarrhoea that affects almost 200 million people and causes nearly 2 million deaths per year. Shigella invades the colonic mucosa, where it initiates an acute inflammation, rich in neutrophils, that initially contributes to tissue damage and eventually resolves the infection. Neutrophils are phagocytic cells that kill microorganisms but it is unclear how neutrophils control pathogenic bacteria expressing virulence factors that manipulate host cells. In contrast to other cells, neutrophils prevent the escape of Shigella from phagocytic vacuoles in which the bacteria are killed. Here we identify human neutrophil elastase (NE) as a key host defence protein: NE degrades Shigella virulence factors at a 1,000-fold lower concentration than that needed to degrade other bacterial proteins. In neutrophils in which NE is inactivated pharmacologically or genetically, Shigella escapes from phagosomes, increasing bacterial survival. NE also preferentially cleaves virulence factors of Salmonella and Yersinia. These findings establish NE as the first neutrophil factor that targets bacterial virulence proteins.     

网络流的层次化分析及其在蠕虫早期检测中的应用

在NetFlow的基础上定义了2种新的网络流：主机层网络流和区域层网络流，并提出了相应的流量特征刻画方法．该定义从主机层和网络层对网络流量进行抽象，实现了底层网络流信息的合并，在不损失关键流量特征的前提下，可大大缩减网络流记录的数量．采用指数加权移动平均控制图模型对所提取的网络流特征进行预测和估计，并结合网络蠕虫的传播特征给出了一种网络蠕虫的早期检测方法．实验结果表明，所提检测方法可以准确地检测到蠕虫在局域网内的早期传播，进而为控制蠕虫传播赢得了宝贵的时间。     

Sinorhizobium meliloti lsrB is involved in alfalfa root nodule development and nitrogen-fixing bacteroid differentiation

Rhizobia interact with host legumes to induce the formation of nitrogen-fixing nodules, which is very important in agriculture and ecology. The development of nitrogen-fixing nodules is stringently regulated by host plants and rhizobial symbionts. In our previous work, a new Sinorhizobium meliloti LysR regulator gene (lsrB) was identified to be essential for alfalfa nodulation. However, how this gene is involved in alfalfa nodulation was not yet understood. Here, we found that this gene was associated with prevention of premature nodule senescence and abortive bacteroid formation. Heterogeneous deficient alfalfa root nodules were induced by the in-frame deletion mutant of lsrB (lsrB1-2), which was similar to the plasmid-insertion mutant, lsrB1. Irregular senescence zones earlier appeared in these nodules where bacteroid differentiation was blocked at different stages from microscopy observations. Interestingly, oxidative bursts were observed in these nodules by DAB staining. The decreased expression of lipopolysaccharide core genes (lpsCDE) was correspondingly determined in these nodules. S. meliloti lipopolysaccharide is required for suppression of oxidative bursts or host cell defense. These findings demonstrate that the S. meliloti lsrB gene is involved in alfalfa root nodule development and bacteroid differentiation by suppressing oxidative bursts or defense responses in host cells.     

虫草的研究与开发利用

本文综述了我国虫草研究和开发利用的最新进展,分别概述了虫草种类与分布、寄主昆虫、生态环境、药用价值、液体深层培养及人工驯化栽培等方面的研究现状。并对虫草研究与利用前景作了展望。     

Plasmids from Staphylococcus aureus replicate in yeast Saccharomyces cerevisiae

It is known that some plasmids, such as RP4, can replicate in many Gram-negative bacteria. Certain small Staphylococcus aureus plasmids have an even broader host range, being able to replicate in not only phylogenetically distant Gram-positive bacteria such as Bacillus subtilis or Streptococcus pneumoniae, but also in the Gram-negative bacterium Escherichia coli. Here we have examined whether these plasmids can also replicate in a lower eukaryote, the yeast Saccharomyces cerevisiae. For this purpose we constructed hybrids between a S. aureus plasmid pC194 and an E. coli plasmid YIp5, which carries a ura-3 gene easy to select for in yeast but cannot replicate in this host. We found that the hybrids transformed yeast with high efficiency (as did hybrids between YIp5 and three other S. aureus plasmids); were maintained extrachromosomally in yeast; and were not modified during residence in yeast. We conclude from this evidence that S. aureus plasmids can replicate in yeast, which raises the questions of whether the replication signals used by prokaryotes and eukaryotes are similar, and how far up the phylogenetic tree the organisms still able to be hosts to S. aureus plasmids may be.     

Mealybug beta-proteobacterial endosymbionts contain gamma-proteobacterial symbionts

Some insects have cultivated intimate relationships with mutualistic bacteria since their early evolutionary history. Most ancient 'primary' endosymbionts live within the cytoplasm of large, polyploid host cells of a specialized organ (bacteriome). Within their large, ovoid bacteriomes, mealybugs (Pseudococcidae) package the intracellular endosymbionts into 'mucus-filled' spheres, which surround the host cell nucleus and occupy most of the cytoplasm. The genesis of symbiotic spheres has not been determined, and they are structurally unlike eukaryotic cell vesicles. Recent molecular phylogenetic and fluorescent in situ hybridization (FISH) studies suggested that two unrelated bacterial species may share individual host cells, and that bacteria within spheres comprise these two species. Here we show that mealybug host cells do indeed harbour both beta- and gamma-subdivision Proteobacteria, but they are not co-inhabitants of the spheres. Rather, we show that the symbiotic spheres themselves are beta-proteobacterial cells. Thus, gamma-Proteobacteria live symbiotically inside beta-Proteobacteria. This is the first report, to our knowledge, of an intracellular symbiosis involving two species of bacteria.     

等待修复的创伤：刑事被害人国家补偿制度研究

近年来，刑事受害人在我国是否应当以及如何得到国家补偿的问题，越来越引起社会的关注。我国尚未建立相应刑事被害人的国家补偿制度，导致我国刑事被害人的权利不能在司法实践中得到应有的保障与维护。刑事被害人国家补偿制度已成为世界范围内刑事立法的大势所趋。建立刑事被害人国家补偿制度有着充分的理论和现实基础，我国建立刑事被害人国家补偿制度的时机日渐成熟。     

A single genetic locus encoded by Yersinia pseudotuberculosis permits invasion of cultured animal cells by Escherichia coli K-12

For many species of pathogenic bacteria, invasion and survival within animal cells is central to establishing a successful host-parasite relationship. Localization within host cells protects the microorganism from host defences, or permits it to cross epithelial barriers and subsequently become systemically distributed. The precise mechanisms that permit entry of bacteria into host tissues are unclear, therefore we have been studying the invasion of epithelial cells by Yersinia pseudotuberculosis. As a first step towards identifying the factors required for this process, we report here the identification of a single genetic locus from this organism that is sufficient to convert the innocuous Escherichia coli K-12 strain into an organism capable of invading cultured animal cells.