Diverse transitional giant fleas from the Mesozoic era of China

Fleas are one of the major lineages of ectoparasitic insects and are now highly specialized for feeding on the blood of birds or mammals. This has isolated them among holometabolan insect orders, although they derive from the Antliophora (scorpionflies and true flies). Like most ectoparasitic lineages, their fossil record is meagre and confined to Cenozoic-era representatives of modern families, so that we lack evidence of the origins of fleas in the Mesozoic era. The origins of the first recognized Cretaceous stem-group flea, Tarwinia, remains highly controversial. Here we report fossils of the oldest definitive fleas--giant forms from the Middle Jurassic and Early Cretaceous periods of China. They exhibit many defining features of fleas but retain primitive traits such as non-jumping hindlegs. More importantly, all have stout and elongate sucking siphons for piercing the hides of their hosts, implying that these fleas may be rooted among the pollinating 'long siphonate' scorpionflies of the Mesozoic. Their special morphology suggests that their earliest hosts were hairy or feathered 'reptilians', and that they radiated to mammalian and bird hosts later in the Cenozoic.     

A draft genome of Yersinia pestis from victims of the Black Death

Technological advances in DNA recovery and sequencing have drastically expanded the scope of genetic analyses of ancient specimens to the extent that full genomic investigations are now feasible and are quickly becoming standard. This trend has important implications for infectious disease research because genomic data from ancient microbes may help to elucidate mechanisms of pathogen evolution and adaptation for emerging and re-emerging infections. Here we report a reconstructed ancient genome of Yersinia pestis at 30-fold average coverage from Black Death victims securely dated to episodes of pestilence-associated mortality in London, England, 1348-1350. Genetic architecture and phylogenetic analysis indicate that the ancient organism is ancestral to most extant strains and sits very close to the ancestral node of all Y. pestis commonly associated with human infection. Temporal estimates suggest that the Black Death of 1347-1351 was the main historical event responsible for the introduction and widespread dissemination of the ancestor to all currently circulating Y. pestis strains pathogenic to humans, and further indicates that contemporary Y. pestis epidemics have their origins in the medieval era. Comparisons against modern genomes reveal no unique derived positions in the medieval organism, indicating that the perceived increased virulence of the disease during the Black Death may not have been due to bacterial phenotype. These findings support the notion that factors other than microbial genetics, such as environment, vector dynamics and host susceptibility, should be at the forefront of epidemiological discussions regarding emerging Y. pestis infections.     

鄱阳湖产太湖短吻银鱼摄食的初步观察

鄱阳湖产太湖短吻银鱼以枝角类、桡足类等浮游动物为主要食料.它们天亮开始摄食,夜间停止,白天连续摄食,其援食速度和消化速度都很快.晴天摄食多,雨天摄食少.周年内,在6、10—11、3月份三次出现摄食高峰.正在产卵的雌鱼停止摄食,产卵后,摄食量又大增.     

The abundance threshold for plague as a critical percolation phenomenon

Percolation theory is most commonly associated with the slow flow of liquid through a porous medium, with applications to the physical sciences. Epidemiological applications have been anticipated for disease systems where the host is a plant or volume of soil, and hence is fixed in space. However, no natural examples have been reported. The central question of interest in percolation theory, the possibility of an infinite connected cluster, corresponds in infectious disease to a positive probability of an epidemic. Archived records of plague (infection with Yersinia pestis) in populations of great gerbils (Rhombomys opimus) in Kazakhstan have been used to show that epizootics only occur when more than about 0.33 of the burrow systems built by the host are occupied by family groups. The underlying mechanism for this abundance threshold is unknown. Here we present evidence that it is a percolation threshold, which arises from the difference in scale between the movements that transport infectious fleas between family groups and the vast size of contiguous landscapes colonized by gerbils. Conventional theory predicts that abundance thresholds for the spread of infectious disease arise when transmission between hosts is density dependent such that the basic reproduction number (R(0)) increases with abundance, attaining 1 at the threshold. Percolation thresholds, however, are separate, spatially explicit thresholds that indicate long-range connectivity in a system and do not coincide with R(0) = 1. Abundance thresholds are the theoretical basis for attempts to manage infectious disease by reducing the abundance of susceptibles, including vaccination and the culling of wildlife. This first natural example of a percolation threshold in a disease system invites a re-appraisal of other invasion thresholds, such as those for epidemic viral infections in African lions (Panthera leo), and of other disease systems such as bovine tuberculosis (caused by Mycobacterium bovis) in badgers (Meles meles).     

Effect of pH values on the extracellular polysaccharide secreted by Acidithiobacillus ferrooxidans during chalcopyrite bioleaching

The pH value plays an important role in the bioleaching of sulphide minerals. The effect of pH values on the extracellular poly-saccharide secreted by Acidithiobacillus ferrooxidans was investigated in different phases of bacterial growth during chalcopyrite bioleach-ing. It is found that extracellular polysaccharide secretion from the cells attached to chalcopyrite is more efficiently than that of the free cells in the bioleaching solution. Three factors, pH values, the concentration of soluble metal ions, and the bacterial growth and metabolism, affect extracellular polysaccharide secretion in the free cells, and are related to the bacterial growth phase. Extracellular polysaccharide secretion from the attached cells is mainly dependent on the pH value of the bacterial culture.     

Increased virulence of Yersinia pseudotuberculosis by two independent mutations

A chromosomally encoded protein, which mediates invasion into HeLa cells was recently identified in Yersinia pseudotuberculosis. The role of this protein (invasin) in the virulence process was not, however, investigated. We show that mutation of the invasin gene in Y. pseudotuberculosis abolishes the ability of the bacteria to invade HeLa cells. When mice were challenged by intraperitoneal injection both the mutant and the wild-type strain produced infections of similar virulence but mutant showed a slower rate of infection after oral challenge. A double mutant, carrying an additional mutation in the gene coding for the Yop1 protein, was also constructed. The double mutant was significantly more virulent than either the wild-type or the corresponding single mutants. Y. pestis, in contrast to Y. pseudotuberculosis lacks the ability to express either invasin or Yop1, sequence analysis of the yopA gene from both Y. pestis and Y. pseudotuberculosis shows that the yopA gene of Y. pestis contains a point-mutation leading to a reading-frame shift. When the yopA+ gene was introduced into Y. pestis the virulence of this strain was reduced. These results may provide insight into the rise and fall of plague epidemics caused by Y. pestis.     

Evolutionary genetics: Ambiguous role of CCR5 in Y. pestis infection

Mecsas and colleagues suggest that a deficiency in the chemokine receptor CCR5 in humans is unlikely to confer protection against plague, based on their study of Yersinia pestis infection in Ccr5-deficient mice. They were testing the hypothesis that a mutation in the CCR5 gene, frequently found in Caucasians, may have been selected for in the past because it provided protection against (bubonic) plague; the mutation, called CCR5Delta32, is characterized by a 32-base-pair deletion. We have also tested this hypothesis by using Y. pestis infection in mice and, in addition, we have done phagocytosis experiments with macrophages from wild-type and Ccr5-deficient mice. Although, like Mecsas et al., we did not see any difference in the survival of the two groups of mice, we did find that there was a significantly reduced uptake of Y. pestis by Ccr5-deficient macrophages in vitro. Our results indicate that the role of Ccr5 in Y. pestis infection may therefore be more complex than previously thought.     

Genome sequence of Yersinia pestis, the causative agent of plague

The Gram-negative bacterium Yersinia pestis is the causative agent of the systemic invasive infectious disease classically referred to as plague, and has been responsible for three human pandemics: the Justinian plague (sixth to eighth centuries), the Black Death (fourteenth to nineteenth centuries) and modern plague (nineteenth century to the present day). The recent identification of strains resistant to multiple drugs and the potential use of Y. pestis as an agent of biological warfare mean that plague still poses a threat to human health. Here we report the complete genome sequence of Y. pestis strain CO92, consisting of a 4.65-megabase (Mb) chromosome and three plasmids of 96.2 kilobases (kb), 70.3 kb and 9.6 kb. The genome is unusually rich in insertion sequences and displays anomalies in GC base-composition bias, indicating frequent intragenomic recombination. Many genes seem to have been acquired from other bacteria and viruses (including adhesins, secretion systems and insecticidal toxins). The genome contains around 150 pseudogenes, many of which are remnants of a redundant enteropathogenic lifestyle. The evidence of ongoing genome fluidity, expansion and decay suggests Y. pestis is a pathogen that has undergone large-scale genetic flux and provides a unique insight into the ways in which new and highly virulent pathogens evolve.     

云南梁河440只小兽体表蚤类和吸虱昆虫寄生状况初步分析

目的:调查分析云南梁河县小兽体表蚤类和吸虱昆虫的寄生状况。方法:用鼠笼、鼠夹加食饵的方法诱捕小兽,用全捕法采集诱捕小兽体表的所有蚤类和吸虱,按"一兽一瓶"置于70%酒精内保存和固定。每只昆虫标本经逐级酒精脱水、透明和干燥后制作成玻片标本,于显微镜下逐一鉴定到种。群落基本结构用物种丰富度(S)、Shannon-Wiener多样性指数(H′)、均匀度(J′)及生态优势度指数(C′)来描述;空间分布格局用扩散系数CI、指数(I)、Cassie指数(CA)及聚块指数(m*/m)进行测定。结果:从所捕获的啮齿目、食虫目7科10属20种440只小兽体表,共采集到蚤类昆虫263只,隶属5科8属10种,方叶栉眼蚤、偏远古蚤、印鼠客蚤和近端远棒蚤二刺亚种为优势种;吸虱昆虫1 316只,隶属3科3属6种,太平洋甲胁虱、缺齿甲胁虱和社鼠甲胁虱为优势种。优势蚤种和优势虱种在其对应的主要宿主体表的寄生表现为聚集型分布。结论:本文调查的440只小兽体表蚤类和吸虱昆虫种类组成比较简单,物种多样性较低,宿主选择特异性吸虱高于蚤类,优势种类在其对应的主要宿主体表的寄生均表现为聚集型分布。     

Evolutionary genetics: CCR5 mutation and plague protection

A recent and prevalent mutation in the chemokine receptor CCR5 in humans of northern European ancestry has been proposed to provide protection against bubonic plague. Here we infect both normal and CCR5-deficient mice with the bacterium Yersinia pestis, the cause of the plague epidemics that wiped out one-third of Europeans in the Middle Ages, and find no difference in either bacterial growth or survival time between the two groups. Unless the pathogenesis of Yersinia infection differs markedly between mice and humans, our results indicate that CCR5 deficiency in people is unlikely to protect against plague.     

Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18.

Salmonella enterica serovar Typhi (S. typhi) is the aetiological agent of typhoid fever, a serious invasive bacterial disease of humans with an annual global burden of approximately 16 million cases, leading to 600,000 fatalities. Many S. enterica serovars actively invade the mucosal surface of the intestine but are normally contained in healthy individuals by the local immune defence mechanisms. However, S. typhi has evolved the ability to spread to the deeper tissues of humans, including liver, spleen and bone marrow. Here we have sequenced the 4,809,037-base pair (bp) genome of a S. typhi (CT18) that is resistant to multiple drugs, revealing the presence of hundreds of insertions and deletions compared with the Escherichia coli genome, ranging in size from single genes to large islands. Notably, the genome sequence identifies over two hundred pseudogenes, several corresponding to genes that are known to contribute to virulence in Salmonella typhimurium. This genetic degradation may contribute to the human-restricted host range for S. typhi. CT18 harbours a 218,150-bp multiple-drug-resistance incH1 plasmid (pHCM1), and a 106,516-bp cryptic plasmid (pHCM2), which shows recent common ancestry with a virulence plasmid of Yersinia pestis.     

云南鼠疫菌随机引物扩增DNA多态性指纹图谱分析

目的：分析云南不同地区、不同年代分离鼠疫菌的基因表型。方法：采用随机引物扩增技术（RAPD）对菌株进行分析。结果：共检测了28株鼠疫菌，除一株外，27株均显示有13条带型，并与假结核菌和小肠结肠炎菌有明显的区别。结论：云南家、野两型鼠疫菌株可能具有相同的随机引物扩增基因表征。     

土壤细菌胞外聚合产物对溶液中U(VI)的去除动力学研究

通过分离和扩培土壤细菌,提取其胞外聚合产物,进行在不同温度下对土壤细菌胞外聚合产物和土壤细菌产量的影响研究,同时进行反应时间对土壤细菌胞外聚合产物去除溶液中U(VI)的影响研究。采用准一级动力学方程和准二级动力学方程对其进行动力学进行分析,研究结果显示在303 K下培养土壤细菌并进行土壤细菌胞外聚合产物的提取较为合适。298 K、308 K和318 K的温度下,土壤细菌胞外聚合产物去除U(VI)在120 min左右达到反应平衡,平衡去除量分别为4. 97 mg/g,8. 75 mg/g,6. 96 mg/g。准二级动力学方程比准一级动力学方程能更好的描述反应进程,说明了土壤细菌胞外聚合产物去除U(VI)是一个以化学机制为主的反应。     

The alpha-lytic protease pro-region does not require a physical linkage to activate the protease domain in vivo

alpha-Lytic protease, an extracellular serine protease of Lysobacter enzymogenes 495, is synthesized as a pre-pro-protein. Previously it has been shown that when expressed in Escherichia coli, the protein is autocatalytically processed in the periplasmic space, and that the functional protease domain accumulates extracellularly. Engineered proteins lacking the 166 amino-acid pro-region were enzymatically inactive and remained cell-associated. By independently expressing the pro- and protease domains in vivo, evidence is provided here that direct covalent linkage is not required for production of active protease. We postulate that the pro-region acts as a template to promote the folding of the protease domain into an active configuration. Our results, combined with recent experiments on the evolutionarily unrelated subtilisin E (ref. 3), suggest that the ability of the pro-region of these bacterial proteases to facilitate folding of their protease domains is not a curiosity of a single system, but may reflect a general property of extracellular bacterial serine proteases.     

X-ray structures of LeuT in substrate-free outward-open and apo inward-open states

Neurotransmitter sodium symporters are integral membrane proteins that remove chemical transmitters from the synapse and terminate neurotransmission mediated by serotonin, dopamine, noradrenaline, glycine and GABA (γ-aminobutyric acid). Crystal structures of the bacterial homologue, LeuT, in substrate-bound outward-occluded and competitive inhibitor-bound outward-facing states have advanced our mechanistic understanding of neurotransmitter sodium symporters but have left fundamental questions unanswered. Here we report crystal structures of LeuT mutants in complexes with conformation-specific antibody fragments in the outward-open and inward-open states. In the absence of substrate but in the presence of sodium the transporter is outward-open, illustrating how the binding of substrate closes the extracellular gate through local conformational changes: hinge-bending movements of the extracellular halves of transmembrane domains 1, 2 and 6, together with translation of extracellular loop 4. The inward-open conformation, by contrast, involves large-scale conformational changes, including a reorientation of transmembrane domains 1, 2, 5, 6 and 7, a marked hinge bending of transmembrane domain 1a and occlusion of the extracellular vestibule by extracellular loop 4. These changes close the extracellular gate, open an intracellular vestibule, and largely disrupt the two sodium sites, thus providing a mechanism by which ions and substrate are released to the cytoplasm. The new structures establish a structural framework for the mechanism of neurotransmitter sodium symporters and their modulation by therapeutic and illicit substances.     

Herpesvirus latency confers symbiotic protection from bacterial infection

All humans become infected with multiple herpesviruses during childhood. After clearance of acute infection, herpesviruses enter a dormant state known as latency. Latency persists for the life of the host and is presumed to be parasitic, as it leaves the individual at risk for subsequent viral reactivation and disease. Here we show that herpesvirus latency also confers a surprising benefit to the host. Mice latently infected with either murine gammaherpesvirus 68 or murine cytomegalovirus, which are genetically highly similar to the human pathogens Epstein-Barr virus and human cytomegalovirus, respectively, are resistant to infection with the bacterial pathogens Listeria monocytogenes and Yersinia pestis. Latency-induced protection is not antigen specific but involves prolonged production of the antiviral cytokine interferon-gamma and systemic activation of macrophages. Latency thereby upregulates the basal activation state of innate immunity against subsequent infections. We speculate that herpesvirus latency may also sculpt the immune response to self and environmental antigens through establishment of a polarized cytokine environment. Thus, whereas the immune evasion capabilities and lifelong persistence of herpesviruses are commonly viewed as solely pathogenic, our data suggest that latency is a symbiotic relationship with immune benefits for the host.     

Structural identification of a bacterial quorum-sensing signal containing boron

Cell-cell communication in bacteria is accomplished through the exchange of extracellular signalling molecules called autoinducers. This process, termed quorum sensing, allows bacterial populations to coordinate gene expression. Community cooperation probably enhances the effectiveness of processes such as bioluminescence, virulence factor expression, antibiotic production and biofilm development. Unlike other autoinducers, which are specific to a particular species of bacteria, a recently discovered autoinducer (AI-2) is produced by a large number of bacterial species. AI-2 has been proposed to serve as a 'universal' signal for inter-species communication. The chemical identity of AI-2 has, however, proved elusive. Here we present the crystal structure of an AI-2 sensor protein, LuxP, in a complex with autoinducer. The bound ligand is a furanosyl borate diester that bears no resemblance to previously characterized autoinducers. Our findings suggest that addition of naturally occurring borate to an AI-2 precursor generates active AI-2. Furthermore, they indicate a potential biological role for boron, an element required by a number of organisms but for unknown reasons.     

福建省黄毛鼠及其体外寄生虫调查专题总结

本文对黄毛鼠及其体外寄生虫进行专题总结,黄毛鼠在我省分布广密度高,其组成及密度沿海高于山区,平原高于丘陵,随着海拔逐渐增高,数量逐渐减少。黄毛鼠外土唾有跳蚤。革螨、恙螨和蜱、,合计近70种之多,为鼠类之冠,由于全省范围内地形,地陀孟貌、气候、海拔及鼠类组成比等条件不同,黄毛鼠体外寄生虫的种类和数量在各地有水平分布和垂直分布的不同,闽东北山区的种类多于东南沿海平原地区。     

Astronomy (communication arising): black holes, fleas and microlithography

Fresnel lenses allow almost perfect imaging in widely different circumstances, but their focus is perfect only for a single wavelength. Wang et al. have shown how the effective bandpass may be widened for X-ray microscopy by using a compound diffractive/refractive lens near to an absorption edge. A compound lens has also been proposed for high-energy astronomy, working well above all absorption edges. Although the scale is very different, we point out here that the principle is the same. Ever since Galileo constructed an astronomical telescope that he was able to reconfigure to study fleas and gnats, astronomy and microscopy have relied on optics that are closely related, but different in detail.