Adaptive divergence for a fitness-related trait among invasive Ambrosia artemisiifolia populations in France

The impact of natural selection on the adaptive divergence of invasive populations can be assessed by testing the null hypothesis that the extent of quantitative genetic differentiation (Q(ST) ) would be similar to that of neutral molecular differentiation (F(ST) ). Using eight microsatellite loci and a common garden approach, we compared Q(ST) and F(ST) among ten populations of an invasive species Ambrosia artemisiifolia (common ragweed) in France. In a common garden study with varying water and nutrient levels, we measured Q(ST) for five traits (height, total biomass, reproductive allocation, above- to belowground biomass ratio, and days to flowering). Although low F(ST) indicated weak genetic structure and strong gene flow among populations, we found significant diversifying selection (Q(ST) > F(ST) ) for reproductive allocation that may be closely related to fitness. It suggests that abiotic conditions may have exerted selection pressure on A. artemisiifolia populations to differentiate adaptively, such that populations at higher altitude or latitude evolved greater reproductive allocation. As previous studies indicate multiple introductions from various source populations of A. artemisiifolia in North America, our results suggest that the admixture of introduced populations may have increased genetic diversity and additive genetic variance, and in turn, promoted the rapid evolution and adaptation of this invasive species.     

葡寡糖对LPS诱导小鼠氧化应激与炎症反应调节作用的研究

本文研究了低、中、高三种不同聚合度葡寡糖(LGOS、MGOS、HGOS)对小鼠氧化应激与炎症反应的调节,并探讨其可能的作用机制。在采食正常日粮基础上,各组小鼠每日分别灌胃生理盐水、低聚果糖(FOS)、LGOS、MGOS、HGOS。21 d后,腹腔注射脂多糖(LPS)诱导小鼠建立氧化应激与炎症反应模型,分别测定LPS刺激后4 h和18 h时血清和肝脏中活性氧(reactive oxygen species,ROS)水平、总抗氧化能力(total antioxidant ca-pacity,T-AOC)、过氧化氢酶(catalase,CAT)、谷胱甘肽过氧化物酶(glutathione peroxidase,GSH-Px)活性、丙二醛(Malondialdehyde,MDA)含量、肝脏中一氧化氮(NO)含量、一氧化氮合酶(nitric oxide synthase,NOS)活性、血清中白细胞介素1(Interleukin-1,IL-1)和肿瘤坏死因子(tumor necrosis factor,TNF-a)含量。结果表明:三种聚合度葡寡糖均能显著降低LPS刺激小鼠血清、肝脏中ROS水平(P<0.05),降低肝脏中NO含量、T-NOS、iNOS活性、血清中炎性细胞因子(IL-1、TNF-a)含量(P<0.05),显著提高总抗氧化能力(T-AOC)和抗氧化酶(CAT、GSH-Px)活性(P<0.05)。葡寡糖具有保护机体免受氧化损伤,减缓炎症反应的作用,并随着平均聚合度(degree ofpolymerization,DP)的增加,其调节功能逐渐增强。     

微生物絮凝剂在养殖废水处理中的应用

微生物絮凝剂作为一种新型的絮凝剂,因其安全、高效等特性,正逐渐成为目前水产养殖废水处理研究的热点。主要从微生物絮凝剂的概念、絮凝机理、特点、研究现状、应用实例等方面,分析了微生物絮凝剂作为水质改良剂在水产养殖中的应用前景,并就今后的研究趋势作了展望。     

The Botrytis cinerea phytotoxin botcinic acid requires two polyketide synthases for production and has a redundant role in virulence with botrydial

The grey mould fungus Botrytis cinerea produces two major phytotoxins, the sesquiterpene botrydial, for which the biosynthesis gene cluster has been characterized previously, and the polyketide botcinic acid. We have identified two polyketide synthase (PKS) encoding genes, BcPKS6 and BcPKS9, that are up-regulated during tomato leaf infection. Gene inactivation and analysis of the secondary metabolite spectra of several independent mutants demonstrated that both BcPKS6 and BcPKS9 are key enzymes for botcinic acid biosynthesis. We showed that BcPKS6 and BcPKS9 genes, renamed BcBOA6 and BcBO9 (for B. cinerea botcinic acid biosynthesis), are located at different genomic loci, each being adjacent to other putative botcinic acid biosynthetic genes, named BcBOA1 to BcBOA17. Putative orthologues of BcBOA genes are present in the closely related fungus Sclerotinia sclerotiorum, but the cluster organization is not conserved between the two species. As for the botrydial biosynthesis genes, the expression of BcBOA genes is co-regulated by the Gα subunit BCG1 during both in vitro and in planta growth. The loss of botcinic acid production does not affect virulence on bean and tomato leaves. However, double mutants that do not produce botcinic acid or botrydial (bcpks6Δbcbot2Δ) exhibit markedly reduced virulence. Hence, a redundant role of botrydial and botcinic acid in the virulence of B. cinerea has been demonstrated.     

The malaria parasite progressively dismantles the host erythrocyte cytoskeleton for efficient egress

Plasmodium falciparum is an obligate intracellular pathogen responsible for worldwide morbidity and mortality. This parasite establishes a parasitophorous vacuole within infected red blood cells wherein it differentiates into multiple daughter cells that must rupture their host cells to continue another infectious cycle. Using atomic force microscopy, we establish that progressive macrostructural changes occur to the host cell cytoskeleton during the last 15 h of the erythrocytic life cycle. We used a comparative proteomics approach to determine changes in the membrane proteome of infected red blood cells during the final steps of parasite development that lead to egress. Mass spectrometry-based analysis comparing the red blood cell membrane proteome in uninfected red blood cells to that of infected red blood cells and postrupture vesicles highlighted two temporally distinct events; (Hay, S. I., et al. (2009). A world malaria map: Plasmodium falciparum endemicity in 2007. PLoS Med. 6, e1000048) the striking loss of cytoskeletal adaptor proteins that are part of the junctional complex, including α/β-adducin and tropomyosin, correlating temporally with the emergence of large holes in the cytoskeleton seen by AFM as early ~35 h postinvasion, and (Maier, A. G., et al. (2008) Exported proteins required for virulence and rigidity of Plasmodium falciparum-infected human erythrocytes. Cell 134, 48-61) large-scale proteolysis of the cytoskeleton during rupture ~48 h postinvasion, mediated by host calpain-1. We thus propose a sequential mechanism whereby parasites first remove a selected set of cytoskeletal adaptor proteins to weaken the host membrane and then use host calpain-1 to dismantle the remaining cytoskeleton, leading to red blood cell membrane collapse and parasite release.     

The Trypanosoma cruzi protease cruzain mediates immune evasion

Trypanosoma cruzi is the causative agent of Chagas' disease. Novel chemotherapy with the drug K11777 targets the major cysteine protease cruzain and disrupts amastigote intracellular development. Nevertheless, the biological role of the protease in infection and pathogenesis remains unclear as cruzain gene knockout failed due to genetic redundancy. A role for the T. cruzi cysteine protease cruzain in immune evasion was elucidated in a comparative study of parental wild type- and cruzain-deficient parasites. Wild type T. cruzi did not activate host macrophages during early infection (<60 min) and no increase in ～P iκB was detected. The signaling factor NF-κB P65 colocalized with cruzain on the cell surface of intracellular wild type parasites, and was proteolytically cleaved. No significant IL-12 expression occurred in macrophages infected with wild type T. cruzi and treated with LPS and BFA, confirming impairment of macrophage activation pathways. In contrast, cruzain-deficient parasites induced macrophage activation, detectable iκB phosphorylation, and nuclear NF-κB P65 localization. These parasites were unable to develop intracellularly and survive within macrophages. IL 12 expression levels in macrophages infected with cruzain-deficient T. cruzi were comparable to LPS activated controls. Thus cruzain hinders macrophage activation during the early (<60 min) stages of infection, by interruption of the NF-κB P65 mediated signaling pathway. These early events allow T. cruzi survival and replication, and may lead to the spread of infection in acute Chagas' disease.     

The real cost of sequencing: higher than you think!

Advances in sequencing technology have led to a sharp decrease in the cost of ''data generation''. But is this sufficient to ensure cost-effective and efficient ''knowledge generation''?     

Comparing and combining distance-based and character-based approaches for barcoding turtles

Molecular barcoding can serve as a powerful tool in wildlife forensics and may prove to be a vital aid in conserving organisms that are threatened by illegal wildlife trade, such as turtles (Order Testudines). We produced cytochrome oxidase subunit one (COI) sequences (650 bp) for 174 turtle species and combined these with publicly available sequences for 50 species to produce a data set representative of the breadth of the order. Variability within the barcode region was assessed, and the utility of both distance-based and character-based methods for species identification was evaluated. For species in which genetic material from more than one individual was available (n = 69), intraspecific divergences were 1.3% on average, although divergences greater than the customary 2% barcode threshold occurred within 15 species. High intraspecific divergences could indicate species with a high degree of internal genetic structure or possibly even cryptic species, although introgression is also probable in some of these taxa. Divergences between species of the same genus were 6.4% on average; however, 49 species were <2% divergent from congeners. Low levels of interspecific divergence could be caused by recent evolutionary radiations coupled with the low rates of mtDNA evolution previously observed in turtles. Complementing distance-based barcoding with character-based methods for identifying diagnostic sets of nucleotides provided better resolution in several cases where distance-based methods failed to distinguish species. An online identification engine was created to provide character-based identifications. This study constitutes the first comprehensive barcoding effort for this seriously threatened order.