Intraspecific molecular phylogeny and phylogeography of the Meriones meridianus (Rodentia: Cricetidae) complex in northern China reflect the processes of desertification and the Tianshan Mountains uplift

The phylogeographical patterns and demographic history of mitochondrial DNA (cytochrome b, N = 327; D‐loop, N = 252) and nuclear DNA (IRBP gene, N = 235) haplotypes were studied for the Meriones meridianus complex in northern China, a desert‐dwelling gerbil species complex. The phylogenetic analyses, which were performed on the separate and combined (mitochondrial + nuclear) datasets, revealed two divergent clades (Clade A and Clade B) corresponding to distinct geographical regions. Clade A contained the haplotypes found mostly in individuals from the Tianshan Mountains area. Clade B contained haplotypes from populations located in other deserts in northern China. The divergence times indicated that the history of the M. meridianus complex was influenced by the uplift of the Tianshan Mountains and climate‐induced habitat fluctuations. In the Pleistocene, the expansion of forests and grasslands during interglacial period led to the isolation of the M. meridianus complex, which preferred to inhabit deserts. Hence, long geological isolation and the M. meridianus complex adaptation to local ecological conditions led to its genetic divergence. Clade A had long‐lasting demographic stability, most likely because the populations of this clade remained in a stable desert environment for a long time. However, the extension of other deserts and disappearance of palaeolakes during the last glacial period resulted in demographic expansion of Clade B. Furthermore, our genetic data indicated that two subspecies may exist within the M. meridianus complex. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 362–383.     

Liquid chromatography tandem mass spectrometry in study of the pharmacokinetics of six steroidal saponins in rats

A rapid, simple and sensitive high-performance liquid chromatography tandem mass spectrometry method was developed and validated for simultaneous determination of six main steroidal saponins in Paris polyphylla in rat plasma. Ginsenoside Rg3 was selected as the internal standard (IS). Plasma samples were pretreated with protein precipitation, and the separation was achieved on a reverse phase Agilent poroshell120 EC-C18 column using a gradient mobile phase system of acetonitrile–water containing 0.1% formic acid. The triple quadruple mass spectrometer was set in negative electrospray ionization mode and multiple reaction monitoring (MRM) was used for six steroidal saponins quantification. The precursors to produce ion transitions monitored for polyphyllin I, polyphyllin II, polyphyllin VI, polyphyllin VII, dioscin, gracillin and IS were m/z 899.5 > 853.4, 1059.5 > 1013.5, 783.4 > 737.4, 1075.5 > 1029.5, 913.5 > 867.4, 929.5 > 883.4 and 819.5 > 783.4, respectively. The intra- and inter-day precisions (RSD%) were less than 13% and the average extraction recoveries ranged from 85% to 97.0% for each analyte. Six steroidal saponins were proved to be stable during sample storage, preparation and analytical procedures. The established method was employed for simultaneous quantification and successfully used for the first time for the pharmacokinetics evaluation of the six main compounds after intragastric administration of P. polyphylla extract in Sprague–Dawley rats.     

A Method for Molecular Analysis of Catalase Gene Diversity in Seawater

Catalase plays an important role in the metabolism of marine bacteria and has potential impact on the marine environment. Four PCR primers were designed to amplify the catalase gene fragments in marine bacteria by applying metagenomic DNA from Yellow Sea surface water as the template. Of the four reproducible target PCR products, the longest one with 900 bp were chosen for catalase gene library construction by the T-vector and the white Escherichia coli colonies in the library was screened through restriction-digesting the reamplified insert fragments by the selected restriction endonuclease MboI, and then the bands of the resulting products were displayed in the agarose gel by electrophoresis. The unique restriction fragment length polymorphism (RFLP) pattern was selected and the corresponding catalase gene fragments were sequenced, which verified that every unique RFLP pattern represented one type of catalase. This PCR–RFLP method above was established to investigate the bacterial catalase diversity in seawater.     

Shotgun Analysis of the Secretome of Fusarium graminearum

Fusarium head blight, caused predominately by Fusarium graminearum, is one of the most destructive diseases of wheat (Triticum aestivum L.) worldwide. To characterize the profile of proteins secreted by F. graminearum, the extracellular proteins were collectively obtained from F. graminearum culture supernatants and evaluated using one-dimensional SDS-PAGE and liquid chromatography-tandem mass spectrometry. A total of 87 proteins have been identified, of which 63 were predicted as secretory proteins including those with known functions. Meanwhile, 20 proteins that are not homologous to genomic sequences with known functions have also been detected. Some of the identified proteins are possible virulence factors and may play extracellular roles during F. graminearum infection. This study provides a valuable dataset of F. graminearum extracellular proteins, and a better understanding of the virulence mechanisms of the pathogen.     

Probiotic Bacillus amyloliquefaciens SC06 Prevents Bacterial Translocation in Weaned Mice

Probiotic is a preparation containing microorganisms that confers beneficial effect to the host. This work assessed whether oral administration of Bacillus amyloliquefaciens SC06 (Ba) could decrease bacterial translocation in weaned mice. Weaned C57BL/6 were randomly allocated into three groups: group I as the control group, group II were treated with 0.85 % NaCl. Group III was administered with probiotic Ba 1 × 10⁹ CFU/day dissolved in 100 μl of 0.85 % NaCl for 30 days. Mice were then sacrificed, and tissue were cultured to determine bacterial translocation. Meanwhile, splenic CD4⁺T cells, CD8⁺T cells, B cells, and macrophages were analysised by FACS. Our results showed that probiotic Ba significantly reduced bacteria translocation compared with the control group and 0.85 % NaCl group (P < 0.05), lower levels of bacteria were detected in the MLN, liver, spleen, and kidney of mice. Moreover, significant increase in percentage and number of macrophages were observed in the spleen of Ba-treated mice compared with the control and 0.85 % NaCl groups. Together, these data indicated that Ba could decrease bacterial translocation in weaned mice. This effect seems to be correlated with the changes of macrophage numbers.     

Nitrogen, organic carbon and sulphur cycling in terrestrial ecosystems: linking nitrogen saturation to carbon limitation of soil microbial processes

Elevated and chronic nitrogen (N) deposition to N-limited terrestrial ecosystems can lead to ‘N saturation’, with resultant ecosystem damage and leaching of nitrate (NO₃ ^?) to surface waters. Present-day N deposition, however, is often a poor predictor of NO₃ ^? leaching, and the pathway of the ecosystem transition from N-limited to N-saturated remains incompletely understood. The dynamics of N cycling are intimately linked to the associated carbon (C) and sulphur (S) cycles. We hypothesize that N saturation is associated with shifts in the microbial community, manifest by a decrease in the fungi-to-bacteria ratio and a transition from N to C limitation. Three mechanisms could lead to lower amount of bioavailable dissolved organic C (DOC) for the microbial community and to C limitation of N-rich systems: (1) Increased abundance of N for plant uptake, causing lower C allocation to plant roots; (2) chemical suppression of DOC solubility by soil acidification; and (3) enhanced mineralisation of DOC due to increased abundance of electron acceptors in the form of ${{\text{SO}}_{ 4}}^{ 2-}$ SO 4 2 ? and NO₃ ^? in anoxic soil micro-sites. Here we consider each of these mechanisms, the extent to which their hypothesised impacts are consistent with observations from intensively-monitored sites, and the potential to improve biogeochemical models by incorporating mechanistic links to the C and S cycles.     

A novel locus essential for spreading of Cytophaga hutchinsonii colonies on agar

Cytophaga hutchinsonii is an aerobic cellulolytic gliding bacterium. The mechanism of its cell motility over surfaces without flagella and type IV pili is not known. In this study, mariner-based transposon mutagenesis was used to identify a new locus CHU_1797 essential for colony spreading on both hard and soft agar surfaces through gliding. CHU_1797 encodes a putative outer membrane protein of 348 amino acids with unknown function, and proteins which have high sequence similarity to CHU_1797 were widespread in the members of the phylum Bacteroidetes. The disruption of CHU_1797 suppressed spreading toward glucose on an agar surface, but had no significant effect on cellulose degradation for cells already in contact with cellulose. SEM observation showed that the mutant cells also regularly arranged on the surface of cellulose fiber similar with that of the wild type strain. These results indicated that the colony spreading ability on agar surfaces was not required for cellulose degradation by C. hutchinsonii. This was the first study focused on the relationship between cell motility and cellulose degradation of C. hutchinsonii.     

Characterization of the sugar-O-methyltransferase LobS1 in lobophorin biosynthesis

Lobophorins A (1) and B (2) belong to a large group of spirotetronate natural products with potent antibacterial and antitumor activities. The cloning of the lobophorin biosynthesis gene cluster from the deep-sea-derived Streptomyces sp. SCSIO 01127 identified a sugar-O-methyltransferase-encoding gene lobS1. The lobS1 inactivation mutant accumulated two new lobophorin analogs 3 and 4, different from 1 and 2 by lacking the 4-methyl group at the terminal l-digitoxose, respectively. Biochemical experiments verified that LobS1 was a SAM-dependent sugar-O-methyltransferase that required divalent metal ions for better activity. Antibacterial assays revealed compounds 3 and 4 were generally less potent than compounds 1 and 2. These findings suggest that the methylation on the terminal digitoxose by LobS1 tailors lobophorin biosynthesis and highlights the importance of this methylation for antibacterial potence.     

Leukotriene D4 induces amyloid-β generation via CysLT1R-mediated NF-κB pathways in primary neurons

Although the pathogenesis of sporadic Alzheimer’s disease (AD) is not clearly understood, neuroinflammation has been known to play a role in the pathogenesis of AD. To investigate a functional link between the neuroinflammation and AD, the effect of leukotriene D4 (LTD4), an inflammatory lipid mediator, was studied on amyloid-β generation in vitro. Application of LTD4 to cell monolayers at concentrations up to 40 nM LTD4 caused increases in the Aβ releases. Concentrations ?40 nM LTD4 decreased neuronal viability. Application of 20 nM LTD4 caused a significant increase in Aβ generation, as assessed by ELISA or Western blotting, without significant cytotoxicity. At this concentration, exposure of neurons to LTD4 for 24 h produced maximal effect in the Aβ generation, and significant increases in the expressions of cysteinyl leukotriene 1 receptor (CysLT₁R) and activity of β- or γ-secretase with complete abrogation by the selective CysLT₁R antagonist pranlukast. Exposure of neurons to LTD4 for 1 h showed activation of NF-κB pathway, by assessing the levels of p65 or phospho-p65 in the nucleus, and either CysLT₁R antagonist pranlukast or NF-κB inhibitor PDTC prevented the nuclear translocation of p65 and the consequent phosphorylation. PDTC also inhibited LTD4-induced elevations of β- or γ-secretase activity and Aβ generation in vitro. Overall, our data show for the first time that LTD4 causes Aβ production by enhancement of β- or γ-secretase resulting from activation of CysLT₁R-mediated NF-κB signaling pathway. These findings provide a novel pathologic link between neuroinflammation and AD.