Enhanced production of exopolysaccharides using industrial grade starch as sole carbon source

Bioprocess and Biosystems Engineering - Industrial grade soluble corn starch was used directly and effectively as the fermentation substrate for microbial exopolysaccharides production. Bacillus...     

Crystal structure of AdoMet radical enzyme 7‐carboxy‐7‐deazaguanine synthase from Escherichia coli suggests how modifications near [4Fe–4S] cluster engender flavodoxin specificity

7‐Carboxy‐7‐deazaguanine synthase, QueE, catalyzes the radical mediated ring contraction of 6‐carboxy‐5,6,7,8‐tetrahydropterin, forming the characteristic pyrrolopyrimidine core of all 7‐deazaguanine natural products. QueE is a member of the S‐adenosyl‐L‐methionine (AdoMet) radical enzyme superfamily, which harnesses the reactivity of radical intermediates to perform challenging chemical reactions. Members of the AdoMet radical enzyme superfamily utilize a canonical binding motif, a CX₃CX?C motif, to bind a [4Fe‐4S] cluster, and a partial (β/α)₆ TIM barrel fold for the arrangement of AdoMet and substrates for catalysis. Although variations to both the cluster‐binding motif and the core fold have been observed, visualization of drastic variations in the structure of QueE from Burkholderia multivorans called into question whether a re‐haul of the defining characteristics of this superfamily was in order. Surprisingly, the structure of QueE from Bacillus subtilis revealed an architecture more reminiscent of the classical AdoMet radical enzyme. With these two QueE structures revealing varying degrees of alterations to the classical AdoMet fold, a new question arises: what is the purpose of these alterations? Here, we present the structure of a third QueE enzyme from Escherichia coli, which establishes the middle range of the spectrum of variation observed in these homologs. With these three homologs, we compare and contrast the structural architecture and make hypotheses about the role of these structural variations in binding and recognizing the biological reductant, flavodoxin. Broader impact statement: We know more about how enzymes are tailored for catalytic activity than about how enzymes are tailored to react with a physiological reductant. Here, we consider structural differences between three 7‐carboxy‐7‐deazaguanine synthases and how these differences may be related to the interaction between these enzymes and their biological reductant, flavodoxin.     

Angiopoietins Modulate Endothelial Adaptation,Glomerular and Podocyte Hypertrophy after Uninephrectomy

Glomerular capillary remodeling is an essential process in the development of glomerular hypertrophy. Angiopoietins, which are important regulators in angiogenesis, plays a role in the development of glomerulus during embryogenesis. Here, we evaluated the influence of angiopoietin on glomerular components and hypertrophy after uninephrectomy in adult male BALB/c mice. The actions of angiopoietin 1 or 2 were systemically antagonized by the subcutaneous administration of antagonists. We observed that the angiopoietin system was activated after uninephrectomy, and that the blockade of angiopoietin 1 or 2 decreased the activation of the angiopoietin receptor—tyrosine kinase with Ig and EGF homology domains-2—and attenuated the development of glomerular and podocyte hypertrophy. The increase in endothelial density staining (anti-CD31) following uninephrectomy was also reversed by angiopoietin 1 or 2 blockades. Glomerular basement thickness and foot process width were observed to decrease in the angiopoietin blockade groups. These changes were associated with the down regulation of the expression of genes for the glomerular matrix and basement membrane, including collagen type IV α1, collagen type IV α2, collagen type IV α5, and laminin α5. Thus, angiopoietin 1 or 2 may play an important role in the development of glomerular hypertrophy after uninephrectomy. A blockade of the angiopoietin system not only influenced the endothelium but also the podocyte, leading to diminished gene expression and morphological changes after uninephrectomy.     

大型和小型萼花臂尾轮虫的遗传和生活史特征比较研究

近年来，有关生物个体大小变异规律的研究已经成为生活史对策研究的重要内容之一。研究发现，大小相似的萼花臂尾轮虫（Brachionus Calyciflorus）母体所产休眠卵孵化出的不同克隆后代个体大小变化显著，其中，最大个体是最小个体体积的6.25倍。推测种群内产生不同大小的后代个体是轮虫应对环境变化的一种适应性进化策略，然而目前对上述不同大小轮虫克隆的遗传和生活史特征的研究尚未见报道。以mtDNA COI基因和rDNA ITS序列作为分子标记，比较了个体大小差异显著的不同克隆萼花臂尾轮虫的遗传分化程度和分类地位，并在不同温度（20℃、25℃、30℃）和不同斜生栅藻（Scenedesmus obliquus）食物密度（1.0×10⁶、3.0×10⁶、5.0×10⁶个/mL）下比较了它们的生活史特征。结果表明，萼花臂尾轮虫种群内个体大小变异并非由于遗传特征的明显分化所导致，大型和小型个体轮虫克隆在两种分子标记上并不构成姐妹种，且两种形态型间还存在共享单倍型。温度、食物密度、轮虫形态型，以及温度和食物密度各自与轮虫形态型之间的交互作用，均显著影响轮虫的生活史特征。小型轮虫在1.0×10⁶个细胞/mL食物密度下显著延长了胚胎和幼体的发育时间，缩短了生殖期历时；大型轮虫在1.0×10⁶个细胞/mL和3.0×10⁶个细胞/mL食物密度下显著延长了幼体的发育时间，但是其用于胚胎发育和生殖的时间却不随食物密度的变化而变化。各温度和食物密度条件下，大型轮虫的生殖期历时、平均寿命和世代时间均显著延长，或有延长趋势；而两者的种群增长能力之间的差异却因温度和食物密度的不同而异。20℃、25℃以及3.0×10⁶个细胞/mL和5.0×10⁶个细胞/mL食物密度下两种形态型轮虫的生殖能力相似；30℃条件下小型轮虫的生殖能力更强；1.0×10⁶个细胞/mL食物密度下大型轮虫的生殖能力更强。小型轮虫在各温度和各食物密度下均未产生混交雌体后代，而大型轮虫在20℃低温下有较高的后代混交率。因此，大型和小型个体轮虫克隆具有显著不同的生活史策略，且利用有性生殖直接产生个体体积明显变异的不同克隆后代是萼花臂尾轮虫适应不可预测环境变化的一种"赌注策略"。