Parasitism ofAphis gossypii (Homoptera: Aphididae) byAllothrombium pulvinum larvae (Acari: Trombidiidae) in cotton fields: spatial dispersion and density dependence

Spatial aspects of the interaction between the aphid host,Aphis gossypii, and its parasite,Allo-thrombium pulvinum larvae, on cotton plants were examined in seven fields in China. For both the host and the parasite, sample variance increased with the mean according to Taylor's power law, which explained a substantial proportion (84–97%) of the variation in the data. Although both the host and parasite showed aggregated distribution on cotton plants, the host aphids aggregated more strongly than the parasites. The host dispersion pattern was not significantly affected by the presence of parasites. Increasing the spatial scales of observation from individual plot to the entire field also had no significant effects on host and parasite dispersion patterns. Parasites aggregated in cotton plants with higher aphid densities in five out of the seventeen samples. Spatial patterns of parasitism were mostly host density-independent (71% of the samples) and sometimes inversely density-dependent (29% of the sample). The processes underlying these patterns were discussed.     

Enhanced catalytic efficiency and enantioselectivity of epoxide hydrolase from Agrobacterium radiobacter AD1 by iterative saturation mutagenesis for (R)-epichlorohydrin synthesis

Applied Microbiology and Biotechnology - Enantioselective hydrolysis of epoxides by epoxide hydrolase (EH) is one of the most attractive approaches for the synthesis of chiral epoxides. So far,...     

Isolation of enantioselective α-hydroxyacid dehydrogenases based on a high-throughput screening method

To isolate enantioselective α-hydroxyacid dehydrogenases (α-HADHs), a high-throughput screening method was established. 2,4-Dinitrophenylhydrazine solution forms a red-brown complex with ketoacid produced during the α-HADH-mediated oxidation of α-hydroxyacid. The complex can be easily quantified by spectrophotometric measurement at 458?nm. The enantioselectivity of α-HADH in each strain can be measured with this colorimetric method using (R)- and (S)-α-hydroxyacid concurrently as substrates to evaluate the apparent enantioselectivity (E _app). The E _app closely matches the value of true enantioselectivity (E _true) determined by HPLC analysis. With this method, a total of 34 stains harboring enantioselective α-HADHs were selected from 526 potential α-HADH-producing microorganisms. Pseudomonas aeruginosa displayed the highest (S)-enantioselective α-HADH activity. This strain appears promising for potential application in industry to produce (R)-α-hydroxyacids. The method described herein represents a useful tool for the high-throughput isolation of enantioselective α-HADHs.     

Rewiring central carbon metabolism for tyrosol and salidroside production in Saccharomyces cerevisiae

Metabolic engineering of Saccharomyces cerevisiae for high-level production of aromatic chemicals has received increasing attention in recent years. Tyrosol production from glucose by S. cerevisiae is considered an environmentally sustainable and safe approach. However, the production of tyrosol and salidroside by engineered S. cerevisiae has been reported to be lower than 2 g/L to date. In this study, S. cerevisiae was engineered with a push-pull-restrain strategy to efficiently produce tyrosol and salidroside from glucose. The biosynthetic pathways of ethanol, phenylalanine, and tryptophan were restrained by disrupting PDC1, PHA2, and TRP3. Subsequently, tyrosol biosynthesis was enhanced with a metabolic pull strategy of introducing PcAAS and EcTyrA^M53I/A354V. Moreover, a metabolic push strategy was implemented with the heterologous expression of phosphoketolase (Xfpk), and then erythrose 4-phosphate was synthesized simultaneously by two pathways, the Xfpk-based pathway and the pentose phosphate pathway, in S. cerevisiae. Furthermore, the heterologous expression of Xfpk alone in S. cerevisiae efficiently improved tyrosol production compared with the coexpression of Xfpk and phosphotransacetylase. Finally, the tyrosol yield increased by approximately 135-folds, compared with that of parent strain. The total amount of tyrosol and salidroside with glucose fed-batch fermentation was over 10 g/L and reached levels suitable for large-scale production.     

Spatial scale of aggregation in three acarine predator species with different degrees of polyphagy

Aggregative responses by the predatory mites, Phytoseiulus persimilis, Typhlodromus occidentalis, and Amblyseius andersoni (Acari: Phytoseiidae), to spatial variation in the density of mobile stages of Tetranychus urticae (Acari: Tetranychidae) were studied over different spatial scales on greenhouse roses. Significant spatial variations in prey numbers per leaflet, per leaf, per branch or per plant were present in all experimental plots. None of the predator species responded to prey numbers per plant, and all searched randomly among plants. Within a plant, the oligophagous P. persimilis searched randomly among branches, but aggregated strongly among leaves within a branch and among leaflets within a leaf. The narrowly polyphagous T. occidentalis searched randomly among leaflets within a leaf and amond leaves within a branch, but aggregated strongly among leaflets or leaves within a plant. The boradly polyphagous A. andersoni searched randomly among leaflets within a leaf, a branch or a plant, and among leaves within a branch or a plant, but distributed themselves more often on branches with lower prey densities. Thus, specialist predators aggregate strongly at lower spatial levels but show random search at higher spatial levels, whereas generalist predators show random search at lower spatial levels but aggregate at higher spatial levels. This is the first empirical evidence demonstrating the relation between the degree of polyphagy and the spatial scale of aggregation. It is also concluded that both the prey patch size (i.e. grain) and predator foraging range (i.e. extent) are important for analyzing spatial scales of predator aggregation. The importance of studying spatial scale of aggregation is also discussed in relation to predator-prey metapopulation dynamics.     

依赖于微环境的TGFβ信号

转化生长因子β（transforming growth factor β，TGFβ）家族成员是一类分泌的细胞因子，在胚胎发育、免疫调节、伤口修复、细胞增殖和抑制等过程中发挥重要作用。其中,TGFβ1、TGFβ2和TGFβ3在进化上最晚出现，并以潜伏态分泌。有别于家族中的大多数成员，TGFβ1-3的信号具有时空区域性，并依赖于其所处的微环境。阐明依赖于微环境的TGFβ信号的多层次调控机制对于理解TGFβ信号在免疫、癌症等生理、病理条件下的功能，以及开发临床治疗策略具有重要意义。本文从TGFβ前体复合物的结构入手，并从TGFβ的激活，配体-受体识别，跨膜信号传导及转录调控等方面，论述依赖于微环境的TGFβ信号的调控机制，同时讨论肿瘤微环境中多效的TGFβ信号，进而对今后的研究方向进行展望。