Determining water level management strategies for lake protection at the ecosystem level

To prevent lake degradation, water level management has been a major focus of research in the past several decades. There are, however, some shortcomings in the traditional studies, and the protection of entire ecosystems is difficult to achieve in practice. In this paper, the framework of a new method for determining ecosystem-based water level regimes (WLRs) for lake protection is proposed. First, historical WLRs are divided into several sub-stages. Then, ecosystem statuses corresponding to different WLRs are quantified and compared. Finally, parameters of optimal and acceptable WLRs are used to determine water level management goals. The proposed method was applied to Baiyangdian Lake, the largest shallow lake in the North China Plain, to test its effectiveness. Results showed that to protect the ecosystem at the optimal status, 50% of the parameter values should fall within the range of the 25th and 75th percentiles of Stage I; and to protect the ecosystem from reverse succession, 50% of the water level parameter values should fall within the range of the 25th and 75th percentiles of Stage II. This method takes ecosystem status into account, and has high practicability in water resources management.     

Matrix metalloproteinase-14 is a mechanically regulated activator of secreted MMPs and invasion

Matrix metalloproteinases (MMPs) are extracellular matrix (ECM) degrading enzymes and have complex and specific regulation networks. This includes activation interactions, where one MMP family member activates another. ECM degradation and MMP activation can be initiated by several different stimuli including changes in ECM mechanical properties or intracellular contractility. These mechanical stimuli are known enhancers of metastatic potential. MMP-14 facilitates local ECM degradation and is well known as a major mediator of cell migration, angiogenesis and invasion. Recently, function blocking antibodies have been developed to specifically block MMP-14, providing a useful tool for research as well as therapeutic applications. Here we utilize a selective MMP-14 function blocking antibody to delineate the role of MMP-14 as an activator of other MMPs in response to changes in cellular contractility and ECM stiffness. Inhibition using function blocking antibodies reveals that MMP-14 activates soluble MMPs like MMP-2 and -9 under various mechanical stimuli in the pancreatic cancer cell line, Panc-1. In addition, inhibition of MMP-14 abates Panc-1 cell extension into 3D gels to levels seen with non-specific pan-MMP inhibitors at higher concentrations. This strengthens the case for MMP function blocking antibodies as more potent and specific MMP inhibition therapeutics.     

Active Site Coupling in PDE:PKA Complexes Promotes Resetting of Mammalian cAMP Signaling

Cyclic 3′5′ adenosine monophosphate (cAMP)-dependent-protein kinase (PKA) signaling is a fundamental regulatory pathway for mediating cellular responses to hormonal stimuli. The pathway is activated by high-affinity association of cAMP with the regulatory subunit of PKA and signal termination is achieved upon cAMP dissociation from PKA. Although steps in the activation phase are well understood, little is known on how signal termination/resetting occurs. Due to the high affinity of cAMP to PKA (K_D ∼ low nM), bound cAMP does not readily dissociate from PKA, thus begging the question of how tightly bound cAMP is released from PKA to reset its signaling state to respond to subsequent stimuli. It has been recently shown that phosphodiesterases (PDEs) can catalyze dissociation of bound cAMP and thereby play an active role in cAMP signal desensitization/termination. This is achieved through direct interactions with the regulatory subunit of PKA, thereby facilitating cAMP dissociation and hydrolysis. In this study, we have mapped direct interactions between a specific cyclic nucleotide phosphodiesterase (PDE8A) and a PKA regulatory subunit (RIα isoform) in mammalian cAMP signaling, by a combination of amide hydrogen/deuterium exchange mass spectrometry, peptide array, and computational docking. The interaction interface of the PDE8A:RIα complex, probed by peptide array and hydrogen/deuterium exchange mass spectrometry, brings together regions spanning the phosphodiesterase active site and cAMP-binding sites of RIα. Computational docking combined with amide hydrogen/deuterium exchange mass spectrometry provided a model for parallel dissociation of bound cAMP from the two tandem cAMP-binding domains of RIα. Active site coupling suggests a role for substrate channeling in the PDE-dependent dissociation and hydrolysis of cAMP bound to PKA. This is the first instance, to our knowledge, of PDEs directly interacting with a cAMP-receptor protein in a mammalian system, and highlights an entirely new class of binding partners for RIα. This study also highlights applications of structural mass spectrometry combined with computational docking for mapping dynamics in transient signaling protein complexes. Together, these results present a novel and critical role for phosphodiesterases in moderating local concentrations of cAMP in microdomains and signal resetting.     

Numerical simulation of the effect of superparamagnetic nanoparticles on microwave rewarming of cryopreserved tissues

In this study, the microwave rewarming process of cryopreserved samples with embedded superparamagnetic (SPM) nanoparticles was numerically simulated. The Finite Element Method (FEM) was used to calculate the coupling of the electromagnetic field and the temperature field in a microwave rewarming system composed of a cylindrical resonant cavity, an antenna source, and a frozen sample phantom with temperature-dependent properties. The heat generated by the sample and the nanoparticles inside the electromagnetic field of the microwave cavity was calculated. The dielectric properties of the biological tissues were approximated using the Debye model, which is applicable at different temperatures. The numerical results showed that, during the rewarming process of the sample phantom without nanoparticles, the rewarming rate was 29.45 °C/min and the maximum temperature gradient in the sample was 3.58 °C/mm. If nanoparticles were embedded in the sample, and the cavity power was unchanged, the rewarming rate was 47.76 °C/min and the maximum temperature gradient in the sample was 1.64 °C/mm. In the presence of SPM nanoparticles, the rewarming rate and the maximum temperature gradient were able to reach 20.73 °C/min and 0.68 °C/mm at the end of the rewarming under the optimized cavity power setting, respectively. The ability to change these temperature behaviors may prevent devitrification and would greatly diminish thermal stress during the rewarming process. The results indicate that the rewarming rate and the uniformity of temperature distribution are increased by nanoparticles. This could be because nanoparticles generated heat in the sample homogeneously and the time-dependent parameters of the sample improved after nanoparticles were homogeneously embedded within it. We were thus able to estimate the positive effect of SPM nanoparticles on microwave rewarming of cryopreserved samples.     

Bioproduction of chiral mandelate by enantioselective deacylation of α-acetoxyphenylacetic acid using whole cells of newly isolated Pseudomonas sp. ECU1011

Substrate-directed screening was carried out to find bacteria that could deacylate O-acetylated mandelic acid from environmental samples. From more than 200 soil isolates, we identified for the first time that Pseudomonas sp. ECU1011 biocatalytically deacylated (S)-α-acetoxyphenylacetic acid with high enantioselectivity (E > 200), yielding (S)-mandelic acid with 98.1% enantiomeric excess (ee) at a 45.5% conversion rate. The catalytic deacylation of (S)-α-acetoxyphenylacetic acid by the resting cell was optimized using a single-factor method to yield temperature and pH optima of 30°C and 6.5, respectively. These optima help to reduce the nonselective spontaneous hydrolysis of the racemic substrate. It was found that substrate concentrations up to 60 mM could be used. 2-Propanol was used as a moderate cosolvent to help the substrate disperse in the aqueous phase. Under optimized reaction conditions, the ee of the residual (R)-α-acetoxyphenylacetic acid could be improved further, to greater than 99%, at a 60% conversion rate. Furthermore, using this newly isolated strain of Pseudomonas sp. ECU1011, three kinds of optically pure analogs of (S)-mandelic acid and (R)-α-acetoxyphenylacetic acid were successfully prepared at high enantiomeric purity.     

Site-directed mutagenesis of disulfide bridges in Aspergillus niger NRRL 3135 phytase (PhyA), their expression in Pichia pastoris and catalytic characterization

Earlier studies have established the importance of five disulfide bridges (DBs) in Aspergillus niger phytase. In this study, the relative importance of each of the individual disulfide bridge is determined by its removal by site-directed mutagenesis of specific cysteines in the cloned A. niger phyA gene. Individually, these mutant phytases were expressed in a Pichia expression system and their product purified and characterized. The removal of disulfide bridge 2 yielded a mutant phytase with a complete loss of catalytic activity. The other disulfide mutants displayed a broad array of altered catalytic properties including a lower optimum temperature from 58°C to 53°C for bridge number 1, 37°C for bridge number 3 and 4, and 42°C for bridge number 5. The pH versus activity profile was also modified in the DB mutants. The pH profile of the wild-type phytase was modified by the DB mutations. In bridge number 1, 3, and 4, the second peak at pH 2.5 was abolished, and in bridge number 5, the peak at pH 5.0 was abolished completely leaving only the pH 2.5. While the K _m was not affected drastically, the turnover number was lowered significantly in bridge number 3, 4, and 5.     

几种讨论式方法在微生物学教学中的应用

为加强学生创新精神与应用能力的培养,解决微生物学教学内容递增与课时递减的矛盾,提出在微生物学课堂上实施辩论赛、学术报告竞赛与讲课比赛等几种讨论式教学方法。实践证明,这些新方法与传统灌输式课堂教学方法相比,具有课堂气氛活跃,教学效果倍增;学生担当评委,师生打成一片;鼓励标新立异,倡导个性发展;弥补课时不足,拓展课程内容等鲜明的优势,人才培养质量显著提高。     

城市河道污水中好氧反硝化菌的分离鉴定与特性

采用富集培养和BTB(溴百里酚蓝)平板法从城市河道污水中筛选、分离获得了一株高效的好氧反硝化菌株ADZ1, 48 h内对硝酸盐的降解率为93.1%, 总氮的去除率为34.7%。16S rRNA测序及系统发育分析结果表明该菌株属于Pseudamonas sp., 经VITEK? 2系统鉴定为Pseudomonas putida。对该菌株的反硝化特性进行了研究, 结果表明, 该菌株以乙醇为最佳碳源, 在碳氮比达到12:1时, 对硝酸盐的去除率达到98%以上, 总氮去除率达到41.3%。该菌株对溶解氧、pH有着广泛的适应性, 菌体活力强, 有着良好的应用前景。     

Inhibition of human lung adenocarcinoma growth using survivint34a by low-dose systematic administration

Anti-apoptosis plays an important role in tumour formation and development. Survivin is a member of the inhibitor of apoptosis (IAP) family, which is a target for anti-cancer drug exploitation was replaced as development. We investigated the role of the homo dominant-negative mutant Survivin-T34A in suppressing human lung adenocarcinomas (A549). The anti-tumour activity of HSurvivinT34A plasmid was evaluated in the A549 cell line and nude mice bearing A549 subcutaneous tumours. Low-dose systemic administration was continuously used. The HSurvivinT34A plasmid (5 µg/one) complexed with a cationic liposome (DOTAP/Chol) significantly inhibited tumour growth in our model. We observed microvessel density degradation by CD31 immunohistochemistry and apoptotic cell increase by TUNEL assay, PI staining and flow cytometric analysis in the treated group. The present findings suggest that the HSurvivinT34A plasmid complexed with a cationic liposome may provide an effective approach to inhibit the growth of human lung adenocarcinomas in vitro and in vivo.     

候鸟迁徙过程中"雄性早现"的六种假说及未来研究热点

"雄性早现"(protandry)是指雄性相对于雌性更早进入繁殖状态或更早到达繁殖地的现象.该文针对候鸟的雄性比雌性在春季时更早到达繁殖地这一现象,介绍了雄性早现的6种假说,即等级优势(rank advantage)假说、敏感性(susceptibility)假说、限制性(constraint)假说、交配机会(mate opportunity)假说、等待代价(waiting cost)假说和配偶选择(mate choice)假说,并通过近年来的研究证据阐述了上述假说对解释候鸟雄性早现的适用性.此外,对鸟类雄性早现未来研究中可能的热点问题做了展望.