Demographic mechanism of a historical bird population collapse reconstructed using museum specimens

Long-term studies of demographic rates provide clues about the external causes of animal population declines, but systematic monitoring is rarely in place until after the decline has occurred. This study evaluates alternative hypotheses about the demographic mechanisms underlying the historical collapse of corncrake (Crexcrex) populations in Britain and Ireland in the late nineteenth and early twentieth centuries using characteristics of museum specimens. The proportion of adult corncrakes that are 1-year old was estimated from feather characteristics of birds collected before, during and after the population decline and showed a marked transitory reduction during the decline. This pattern would be expected if the decline was caused by a large reduction in the recruitment of young birds to the breeding population and is the opposite of what would be expected if a change in adult survival had caused the decline. These results are consistent with previous suggestions that the corncrake population decline was caused by adverse effects on breeding productivity caused by the mechanization of the harvesting of hay crops.     

Kaposi's sarcoma-associated herpesvirus OX2 glycoprotein activates myeloid-lineage cells to induce inflammatory cytokine production

Kaposi's sarcoma is an inflammatory cytokine-mediated angioproliferative disease which is triggered by infection by Kaposi's sarcoma-associated herpesvirus (KSHV). KSHV contains an open reading frame, K14, that has significant homology with cellular OX2, designated viral OX2 (vOX2). In this report, we demonstrate that vOX2 encodes a glycosylated cell surface protein with an apparent molecular mass of 55 kDa. Purified glycosylated vOX2 protein dramatically stimulated primary monocytes, macrophages, and dendritic cells to produce the inflammatory cytokines interleukin 1beta (IL-1beta), IL-6, monocyte chemoattractant protein 1, and TNF-alpha. Furthermore, expression of vOX2 on B lymphocytes stimulated monocytes to produce inflammatory cytokines in mixed culture. These results demonstrate that like its cellular counterpart, vOX2 targets myeloid-lineage cells, but unlike cellular OX2, which delivers a restrictive signal, KSHV vOX2 provides an activating signal, resulting in the production of inflammatory cytokines. Thus, this is a novel viral strategy where KSHV has acquired the cellular OX2 gene to induce inflammatory cytokine production, which potentially promotes the cytokine-mediated angiogenic proliferation of KSHV-infected cells.     

羟自由基对人红细胞磷脂酰乙醇胺脂质体相变性质的影响

研究了过氧化氢与亚铁离子体系产生的羟自由基对人红细胞膜磷脂酸乙醇胺(PE)脂质体相变性质的影响.结果表明,羟自由基导致脂质体不饱和脂肪酸链的含量明显降低和丙二醛(MDA)含量显著升高,同时其膜流动性随之下降.在室温下,羟自由基诱使PF脂质体冰冻断裂面出现脂质颗粒,说明羟自由基通过脂质过氧化作用可促进PE脂质体从脂双层转变为非双层结构.     

枯草芽孢杆菌渗透压调节基因proB的克隆和表达

用PCR扩增的方法从耐盐的枯草杆菌中克隆出一个13kb长的DNA片段,经功能检测,证明正向插入片段与大肠杆菌的脯氨酸营养缺陷特性(proB-)能够营养互补。含有该重组质粒的大肠杆菌DH5α在基本培养基上的耐盐能力从2%提高至4%。通过引物步行法测定了该插入片段的核苷酸序列。利用DNAsis软件进行序列分析发现,该片段第122～1235bp核苷酸编码一个由370个氨基酸组成的蛋白质分子,其上游存在非典型的-10区,典型的-35区和核糖体结合位点,起始密码子处有最佳翻译起始效率的侧翼核苷酸序列。将其与Genebank中的已知基因的序列和编码的氨基酸序列进行同源性比较,结果表明该片段与枯草杆菌168的核苷酸序列、氨基酸序列的同源性分别为81%和90%。证明该基因确实是一个proB基因。通过与三十个不同种属微芽生物proB基因的氨基酸序列比较,发现该蛋白存在有可能与形成酶的活性中心和三维结构有密切关系的几个绝对保守的区域。     

Structural arrangement and conformational dynamics of the gamma subunit of the Na+/K+-ATPase

The Na+/K+-ATPase couples the chemical energy in ATP to transport Na+ and K+ across the plasma membrane against a concentration gradient. The ion pump is composed of two mandatory subunits: the alpha subunit, which is the major catalytic subunit, and the beta subunit, which is required for proper trafficking of the complex to the plasma membrane. In some tissues, the ion pump also contains an optional third subunit, gamma, which modulates the pump activity. To examine the conformational dynamics of the gamma subunit during ion transport and its position in relation to the alpha and the beta subunits, we have used fluorescence resonance energy transfer under voltage clamp conditions. From these experiments, evidence is provided that the gamma subunit is located adjacent to the M2-M6-M9 pocket of the alpha subunit at the transmembrane-extracellular interface. We have also used fluorescence resonance energy transfer to investigate the relative movement of the three subunits as the ion pump shuttles between the two main conformational states, E1 and E2, as described by the Albers-Post scheme. The results from this study suggest that there is no relative change in distance between the alpha and gamma subunits but there is a relative change in distance between the beta and gamma subunits during the E2 to E1 transition. It was also observed that labeling the gamma subunit at specific residues with fluorophores induces a decrease in K+-induced stationary current. This result could be due to a perturbation in the K+ branch of the reaction cycle of the pump, representing a new way to inhibit the pump.     

A chimeric N-terminal Escherichia coli--C-terminal Rhodobacter sphaeroides FliG rotor protein supports bidirectional E. coli flagellar rotation and chemotaxis

Flagellate bacteria such as Escherichia coli and Salmonella enterica serovar Typhimurium typically express 5 to 12 flagellar filaments over their cell surface that rotate in clockwise (CW) and counterclockwise directions. These bacteria modulate their swimming direction towards favorable environments by biasing the direction of flagellar rotation in response to various stimuli. In contrast, Rhodobacter sphaeroides expresses a single subpolar flagellum that rotates only CW and responds tactically by a series of biased stops and starts. Rotor protein FliG transiently links the MotAB stators to the rotor, to power rotation and also has an essential function in flagellar export. In this study, we sought to determine whether the FliG protein confers directionality on flagellar motors by testing the functional properties of R. sphaeroides FliG and a chimeric FliG protein, EcRsFliG (N-terminal and central domains of E. coli FliG fused to an R. sphaeroides FliG C terminus), in an E. coli FliG null background. The EcRsFliG chimera supported flagellar synthesis and bidirectional rotation; bacteria swam and tumbled in a manner qualitatively similar to that of the wild type and showed chemotaxis to amino acids. Thus, the FliG C terminus alone does not confer the unidirectional stop-start character of the R. sphaeroides flagellar motor, and its conformation continues to support tactic, switch-protein interactions in a bidirectional motor, despite its evolutionary history in a bacterium with a unidirectional motor.     

A Polyketide Synthase Gene Required for Biosynthesis of the Aflatoxin-like Toxin, Dothistromin

Dothistromin is a polyketide toxin, produced by a fungal forest pathogen, with structural similarity to the aflatoxin precursor versicolorin B. Biochemical and genetic studies suggested that there are common steps in the biosynthetic pathways for these metabolites and showed similarities between some of the genes. A polyketide synthase gene (pksA) was isolated from dothistromin-producing Dothistroma septosporum by hybridization with an aflatoxin ortholog from Aspergillus parasiticus. Inactivation of this gene in D. septosporum resulted in mutants that could not produce dothistromin but that could convert exogenous aflatoxin precursors, including norsolorinic acid, into dothistromin. The mutants also had reduced asexual sporulation compared to the wild type. So far four other genes are known to be clustered immediately alongside pksA. Three of these (cypA, moxA, avfA) are predicted to be orthologs of aflatoxin biosynthetic genes. The other gene (epoA), located between avfA and moxA, is predicted to encode an epoxide hydrolase, for which there is no homolog in either the aflatoxin or sterigmatocystin gene clusters. The pksA gene is located on a small chromosome of ~1.3 Mb in size, along with the dothistromin ketoreductase (dotA) gene.     

Oxidative stress and antioxidant capacity of a terrestrially hibernating hatchling turtle

Hatchlings of the painted turtle, Chrysemys picta, hibernate terrestrially and can survive subfreezing temperatures by supercooling or by tolerating the freezing of their tissues. Whether supercooled or frozen, an ischemic hypoxia develops because tissue perfusion is limited by low temperature and/or freezing. Oxidative stress can occur if hatchlings lack sufficient antioxidant defenses to minimize or prevent damage by reactive oxygen species. We examined the antioxidant capacity and indices of oxidative damage in hatchling C. picta following survivable, 48 h bouts of supercooling (−6°C), freezing (−2.5°C), or hypoxia (4°C). Samples of plasma, brain, and liver were collected after a 24 h period of recovery (4°C) and assayed for Trolox-equivalent antioxidant capacity (TEAC), thiobarbituric acid reactive substances (TBARS), and carbonyl proteins. Antioxidant capacity did not vary among treatments in any of the tissues studied. We found a significant increase in TBARS in plasma, but not in the brain or liver, of frozen/thawed hatchlings as compared to untreated controls. No changes were found in the concentration of TBARS or carbonyl proteins in supercooled or hypoxia-exposed hatchlings. Our results suggest that hatchling C. picta have a well-developed antioxidant defense system that minimizes oxidative damage during hibernation.     

普洱熟茶后发酵优势菌臭曲霉的生物学特性

为了开发普洱熟茶生产的规范技术,本文对普洱茶后发酵优势芮之一的臭曲霉的生物学特性进行了研究.结果表明,该菌株对酸碱度有广幅的适应性;在以硫酸铵或豆饼粉为氮源,玉米粉或果糖为碳源的培养基中生长迅速;培养温度以30℃最为适宜.同时,对菌落的牛长规律及形态特征进行了观察与分析.研究结果为该菌株的大量培养,以及普洱茶的规范化生产技术提供了基础.