Host plant development, water level and water parameters shape Phragmites australis-associated oomycete communities and determine reed pathogen dynamics in a large lake

In a 3-year-study, we analysed the population dynamics of the reed pathogen Pythium phragmitis and other reed-associated oomycetes colonizing fresh and dried reed leaves in the littoral zone of a large lake. Oomycete communities derived from internal transcribed spacer clone libraries were clearly differentiated according to substrate and seasonal influences. In fresh leaves, diverse communities consisting of P. phragmitis and other reed-associated pathogens were generally dominant. Pythium phragmitis populations peaked in spring with the emergence of young reed shoots, and in autumn after extreme flooding events. In summer it decreased with falling water levels, changing water chemistry and rising temperatures. Another Pythium species was also highly abundant in fresh leaves throughout the year and might represent a new, as-yet uncultured reed pathogen. In dried leaves, reed pathogens were rarely detected, whereas saprophytic species occurred abundantly during all seasons. Saprophyte communities were less diverse, less temperature sensitive and independent of reed development. In general, our results provide evidence for the occurrence of highly specialized sets of reed-associated oomycetes in a natural reed ecosystem. Quantitative analyses (clone abundances and quantitative real-time PCR) revealed that the reed pathogen P. phragmitis is particularly affected by changing water levels, water chemistry and the stage of reed development.     

植物响应病原菌胁迫的蛋白质组学研究进展

随着拟南芥、水稻等模式植物基因组测序的完成,植物基因组学的研究重点已经转变为功能基因组学研究。蛋白质组学成为后基因组时代的重要研究手段,它有助于从分子水平上了解植物功能。主要介绍了双向电泳技术、生物质谱、蛋白质质谱数据的生物信息学分析等蛋白质组学研究的主要技术手段及植物应答病原菌胁迫的蛋白质组学研究进展,并对蛋白质组学在研究植物抗病机制方面的应用前景做出展望。     

Evidence for Transepithelial Dendritic Cells in Human H. pylori Active Gastritis

Background:  Despite extensive experimental investigation stressing the importance of bacterial interaction with dendritic cells (DCs), evidence regarding direct interaction of Helicobacter pylori or its virulence products with DCs in the human gastric mucosa is lacking.
Methods:  Human gastric mucosa biopsies, with or without H. pylori infection and active inflammation, were investigated at light and electron microscopy level with immunocytochemical tests for bacterial products (VacA, urease, outer membrane proteins) and DC markers (DC-SIGN, CD11c, CD83) or with the DC-labeling ZnI₂-OsO₄ technique. Parallel tests with cultured DCs were carried out.
Results:  Cells reproducing ultrastructural and cytochemical patterns of DCs were detected in the lamina propria and epithelium of heavily infected and inflamed (but not of normal) mucosa, where DC luminal endings directly contact H. pylori and take up their virulence products. Cytotoxic changes (mitochondrial swelling, cytoplasmic vacuolation, autophagy) were observed in intraepithelial DCs and reproduced in cultured DCs incubated with H. pylori broth culture filtrates to obtain intracellular accumulation of VacA and urease. Granulocytes were also seen to contact and heavily phagocytose luminal H. pylori , while macrophages remained confined to basal epithelium, though taking up bacteria and bacterial products.
Conclusion:  Human DCs can enter H. pylori -infected gastric epithelium, in association with other innate immunity cells, to take up bacteria and their virulence products. This process is likely to be important for bacterial sensing and pertinent immune response; however, it may also generate DC cytotoxic changes potentially hampering their function.     

Complete genome sequence of Methanoplanus petrolearius type strain (SEBR 4847)

Segniliparus rotundus Butler 2005 is the type species of the genus Segniliparus, which is currently the only genus in the corynebacterial family Segniliparaceae. This family is of large interest because of a novel late-emerging genus-specific mycolate pattern. The type strain has been isolated from human sputum and is probably an opportunistic pathogen. Here we describe the features of this organism, together with the complete genome sequence and annotation. This is the first completed genome sequence of the family Segniliparaceae. The 3,157,527 bp long genome with its 3,081 protein-coding and 52 RNA genes is part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Development of a quantitative Real‐Time TaqMan PCR assay for determination of the minimal dose of Mycoplasma hyopneumoniae strain 116 required to induce pneumonia in SPF pigs

Aims: A triplex real‐time PCR assay to quantify Mycoplasma hyopneumoniae in specimens from live and dead pigs was developed and validated. The minimal dose of Myc. hyopneumoniae required to induce pneumonia in specific pathogen‐free pigs was determined. Methods and Results: This TaqMan test simultaneously detected three genes encoding the proteins P46, P97 and P102. All Myc. hyopneumoniae strains analysed were detected, including strains isolated in three countries (France, England and Switzerland) and from several pig farms (n = 33), and the test was specific. The estimated detection thresholds were 1·3 genome equivalents (μl^?1) for the targets defined in p97 and p102 genes and 13 genome equivalents (μl^?1) for the segment defined in the p46 gene. This test was used to quantify Myc. hyopneumoniae in specimens sampled from experimentally infected pigs. In live pigs, c. 10⁷, 10⁸ and 10¹⁰ genome equivalents (ml^?1) of Myc. hyopneumoniae were detected in the nasal cavities, tonsils and trachea samples, respectively. In dead pigs, 10⁸–10¹⁰ genome equivalents (ml^?1) of Myc. hyopneumoniae were detected in the lung tissue with pneumonia. The estimated minimal dose of Myc. hyopneumoniae required to induce pneumonia was 10⁵ colour‐changing units (CCU) per pig (corresponding to 10⁸ mycoplasmas). Conclusion: The triplex RT‐PCR test was validated and can be used for testing samples taken on the pig farms. Significance and Impact of the Study: This test should be a very useful tool in pig herds to control enzootic pneumonia or healthy carrier pigs and to study the dynamics of Myc. hyopneumoniae infections.     

Parasitism, predation and the evolution of animal personalities

Trade-offs between behavioural traits promoting high life-history productivity and mortality may fuel the evolution of animal personalities. We propose that parasites, including pathogens, impose fitness costs comparable to those from predators, and influence the adaptiveness of personality traits associated with productivity (PAPs). Whether personality traits are adaptive or not may also depend on individual immunological capacity. We illustrate this using a conceptual example in which the optimal level of PAPs depends on predation, parasitism and host compensation (resistance and tolerance) of parasitism's negative effects. We assert that inherent differences in host immune function can produce positive feedback loops between resource intake and compensation of parasitism's costs, thereby providing variation underlying the evolution of stable personalities. Our approach acknowledges the condition dependence of immune function and co-evolutionary dynamics between hosts and parasites.     

Controls on pathogen species richness in plants' introduced and native ranges: roles of residence time, range size and host traits

Introduced species escape many pathogens and other enemies, raising three questions. How quickly do introduced hosts accumulate pathogen species? What factors control pathogen species richness? Are these factors the same in the hosts' native and introduced ranges? We analysed fungal and viral pathogen species richness on 124 plant species in both their native European range and introduced North American range. Hosts introduced 400 years ago supported six times more pathogens than those introduced 40 years ago. In hosts' native range, pathogen richness was greater on hosts occurring in more habitat types, with a history of agricultural use and adapted to greater resource supplies. In hosts' introduced range, pathogen richness was correlated with host geographic range size, agricultural use and time since introduction, but not any measured biological traits. Introduced species have accumulated pathogens at rates that are slow relative to most ecological processes, and contingent on geographic and historic circumstance.     

The antibacterial activity of phospholipase A2 type IIA is regulated by the cooperative lipid chain melting behavior in Staphylococcus aureus

As one of its primary physiological functions, sPLA₂-IIA appears to act as an antibacterial agent. In particular, sPLA₂-IIA shows high activity towards Gram-positive bacteria such as Staphylococcus aureus (S. aureus). This antibacterial activity results from the preference of the enzyme towards membranes enriched in anionic lipids, which is a common feature of bacterial membranes. An intriguing aspect observed in a variety of bacterial membranes is the presence of a broad but cooperative lipid chain melting event where the lipids in the membrane transition from a solid-ordered (so) into a liquid-disordered (ld) state close to physiological temperatures. It is known that the enzyme is sensitive to the level of lipid packing, which changes sharply between the so and the ld states. Therefore, it would be expected that the enzyme activity is regulated by the bacterial membrane thermotropic behavior. We determine by FTIR the thermotropic lipid chain melting behavior of S. aureus and find that the activity of sPLA₂-IIA drops sharply in the so state. The activity of the enzyme is also evaluated in terms of its effects on cell viability, showing that cell survival increases when the bacterial membrane is in the so state during enzyme exposure. These results point to a mechanism by which bacteria can develop increased resistance towards antibacterial agents that act on the membrane through a cooperative increase in the order of the lipid chains. These results show that the physical behavior of the bacterial membrane can play an important role in regulating physiological function in an in vivo system.