西双版纳热带山地雨林生物量研究

观测了西双版纳山地气候,建立了山地雨林生物量回归方程,调查了海拔1 100~1 820 m范围5块样地(面积0.16~0.25 hm2)的热带山地雨林生物量。结果表明,海拔1 105和1 610 m的年平均温度分别为20.1和16.6℃,年降雨量分别为1 659和2 011 mm,旱季(11~4月)降雨量分别为295和283mm,年平均相对湿度分别为81%和84%;5块样地生物量变化为256.4~368.6 t.hm-2,平均为312.6t.hm-2,其中乔木占97.1%、木质藤本占1.2%、幼树和灌木占1.3%、草本和幼苗占0.4%;采用热带季节雨林生物量回归方程估计山地雨林生物量,会使得总生物量以及树干和树根生物量高估38.3%~61.5%,树枝生物量低估7.6%~30.8%。可见,西双版纳山地海拔增加导致雨季降雨量增加,山地雨林生物量较热带季节雨林降低32.6%,季节雨林生物量方程不适用于山地雨林。     

水盾草科系统位置评述

水盾草科（Cabombaceae）是双子叶植物。水盾草科包括2属：水盾草属（Cabomba Aublet．）和莼菜属（Brasenia Schreb．）。形态学研究显示水盾草科具有许多原始性状,而且在其适应水生环境的过程中经历了性状退化。水盾草科又被称为“古草本”。最新的分子系统发育研究显示,水盾草科是现存被子植物系统树基部ANITA类群的成员之一。但有关水盾草科的系统位置存在争议。被子植物的起源与早期分化一直是植物学家关注的热点。本文对该科系统位置的研究历史与现状进行评述。     

Molecular docking and structure–activity relationship studies on benzothiazole based non-peptidic BACE-1 inhibitors

A similarity search on the structural analogs of an inhibitor of BACE-1 with IC₅₀ 2.8 μM, which contained a P1 benzothiazole group together with a triazine ring linked by a secondary amine group, was described in this Letter and some more potent inhibitors against BACE-1 were identified. The most potent compound 5 (IC₅₀ = 0.12 μM) increases the inhibitory potency by 24 folds. Our results suggest that a pyrrolidinyl side group at the P3′ and P4′ of the inhibitors are favored for strong inhibition and a small aromatic group at the P4 position is also essential to the potency.     

Identification of a sub-micromolar,non-peptide inhibitor of β-secretase with low neural cytotoxicity through in silico screening

Nowadays identification of novel non-peptide β-secretase (BACE-1, hereinafter) inhibitors with low cytotoxicity and good blood–brain barrier (BBB) property holds common interest of drug discovery for Alzheimer’s disease. Twenty SPECS compounds were tested in BACE-1 FRET assays and methylthiazoletetrazolium (MTT) cytotoxicity experiment. Two compounds: 2 and 15 demonstrated IC₅₀ values of 0.53 and 9.4 μM. In addition, 2 showed least toxic effect to the neuroblastoma cells. The results from both in silico and in vitro studies provided new pharmacophoric entities for chemical synthesis and optimization on the current discovered BACE-1 small molecule inhibitors.     

Hydrophilic interaction liquid chromatography-tandem mass spectrometry for the determination of adefovir in human plasma and its application to a pharmacokinetic study

A selective, rapid and sensitive hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC–MS/MS) method was developed for the first time to determine adefovir in human plasma and applied to a pharmacokinetic study. Plasma samples were prepared by protein precipitation with methanol followed by a further cleaning using dichloromethane. The chromatographic separation was carried out on an ACQUITY UPLC™ BEH HILIC column with the mobile phase of methanol–water–formic acid (85:15:0.2, v/v/v). The detection was performed on a triple-quadrupole tandem mass spectrometer with multiple reaction monitoring (MRM) mode via electrospray ionization (ESI) source. The method was rapid with a run time of 3 min per sample. The linear calibration curves were obtained in the concentration range of 1.02–102 ng/mL (r² ≥ 0.99) with the lower limit of quantification (LLOQ) of 1.02 ng/mL. The intra- and inter-day precision (relative standard deviation, R.S.D.) values were below 12% and the accuracy (relative error, R.E.) was from 0.6% to 3.2% at all quality control (QC) levels. The method was applicable to clinical pharmacokinetic study of adefovir in healthy volunteers after oral administration of adefovir dipivoxil tablet.     

Ultrasound-Mediated DNA Transformation in Thermophilic Gram-Positive Anaerobes

Background

Thermophilic, Gram-positive, anaerobic bacteria (TGPAs) are generally recalcitrant to chemical and electrotransformation due to their special cell-wall structure and the low intrinsic permeability of plasma membranes.

Methodology/Principal Findings

Here we established for any Gram-positive or thermophiles an ultrasound-based sonoporation as a simple, rapid, and minimally invasive method to genetically transform TGPAs. We showed that by applying a 40 kHz ultrasound frequency over a 20-second exposure, Texas red-conjugated dextran was delivered with 27% efficiency into Thermoanaerobacter sp. X514, a TGPA that can utilize both pentose and hexose for ethanol production. Experiments that delivered plasmids showed that host-cell viability and plasmid DNA integrity were not compromised. Via sonoporation, shuttle vectors pHL015 harboring a jellyfish gfp gene and pIKM2 encoding a Clostridium thermocellum β-1,4-glucanase gene were delivered into X514 with an efficiency of 6×10² transformants/µg of methylated DNA. Delivery into X514 cells was confirmed via detecting the kanamycin-resistance gene for pIKM2, while confirmation of pHL015 was detected by visualization of fluorescence signals of secondary host-cells following a plasmid-rescue experiment. Furthermore, the foreign β-1,4-glucanase gene was functionally expressed in X514, converting the host into a prototypic thermophilic consolidated bioprocessing organism that is not only ethanologenic but cellulolytic.

Conclusions/Significance

In this study, we developed an ultrasound-based sonoporation method in TGPAs. This new DNA-delivery method could significantly improve the throughput in developing genetic systems for TGPAs, many of which are of industrial interest yet remain difficult to manipulate genetically.     

Functional biogeography as evidence of gene transfer in hypersaline microbial communities

Background

Horizontal gene transfer (HGT) plays a major role in speciation and evolution of bacteria and archaea by controlling gene distribution within an environment. However, information that links HGT to a natural community using relevant population-genetics parameters and spatial considerations is scarce. The Great Salt Lake (Utah, USA) provides an excellent model for studying HGT in the context of biogeography because it is a contiguous system with dispersal limitations due to a strong selective salinity gradient. We hypothesize that in spite of the barrier to phylogenetic dispersal, functional characteristics—in the form of HGT—expand beyond phylogenetic limitations due to selective pressure.

Methodology and Results

To assay the functional genes and microorganisms throughout the GSL, we used a 16S rRNA oligonucleotide microarray (Phylochip) and a functional gene array (GeoChip) to measure biogeographic patterns of nine microbial communities. We found a significant difference in biogeography based on microarray analyses when comparing Sørensen similarity values for presence/absence of function and phylogeny (Student''s t-test; p = 0.005).

Conclusion and Significance

Biogeographic patterns exhibit behavior associated with horizontal gene transfer in that informational genes (16S rRNA) have a lower similarity than functional genes, and functional similarity is positively correlated with lake-wide selective pressure. Specifically, high concentrations of chromium throughout GSL correspond to an average similarity of chromium resistance genes that is 22% higher than taxonomic similarity. This suggests active HGT may be measured at the population level in microbial communities and these biogeographic patterns may serve as a model to study bacteria adaptation and speciation.