Changes in freshwater sediment microbial populations during fermentation of crude glycerol

BackgroundThis work studied how the exposure to an unusual substrate forced a change in microbial populations during anaerobic fermentation of crude glycerol, a by-product of biodiesel production, with freshwater sediment used as an inoculum.ResultsThe microbial associations almost completely (99.9%) utilized the glycerol contained in crude glycerol 6 g L⁻¹ within four days, releasing gases, organic acids (acetic, butyric) and alcohols (ethanol, n-butanol) under anaerobic conditions. In comparison with control medium without glycerol, adding crude glycerol to the medium increased the amount of ethanol and n-butanol production and it was not significantly affected by incubation temperature (28 °C or 37 °C), nor incubation time (4 or 8 d), but it resulted in reduced amount of butyric acid. Higher volume of gas was produced at 37 °C despite the fact that the overall bacterial count was smaller than the one measured at 20 °C. Main microbial phyla of the inoculum were Actinobacteria, Proteobacteria and Firmicutes. During fermentation, significant changes were observed and Firmicutes, especially Clostridium spp., began to dominate, and the number of Actinobacteria and Gammaproteobacteria decreased accordingly. Concentration of Archaea decreased, especially in medium with crude glycerol. These changes were confirmed both by culturing and culture-independent (concentration of 16S rDNA) methods.ConclusionsCrude glycerol led to the adaptation of freshwater sediment microbial populations to this substrate. Changes of microbial community were a result of a community adaptation to a new source of carbon.How to cite: Paiders M, Nikolajeva V, Makarenkova G, et al. Changes in freshwater sediment microbial populations during fermentation of crude glycerol. Electron J Biotechnol 2021;49. https://doi.org/10.1016/j.ejbt.2020.10.007     

Free Radical Scavenging Properties of Skin and Pulp Extracts of Different Grape Cultivars In Vitro and Attenuation of H2O2-Induced Oxidative Stress in Liver Tissue Ex Vivo

Grapes are the richest source of antioxidants due to the presence of potent bioactive phytochemicals. In this study, the phytochemical contents, scavenging activities and protective role against H₂O₂-induced oxidative stress in liver tissue ex vivo of four grape (Vitis vinifera) cultivars extracts, namely Flame seedless (black), Kishmish chorni (black with reddish brown), Red globe (red) and Thompson seedless mutant (green), were evaluated. The total phenolics and flavonoids content in pulp or skin fractions of different grape cultivars were in the range of 47.6–310 mg gallic acid equivalent/g fresh weight (fw), and 46.6–733.3 µg catechin equivalent/g fw respectively. The scavenging activities in skin of different grape varieties against 2,2-diphenyl-1-picrylhydrazyl (44–58 %), hydrogen peroxide (15.3–18.6 %), and hydroxyl radicals (50–85 %), were higher than pulp of the corresponding cultivars. These scavenging activities of grape extracts were found to be significantly (p < 0.01) correlated with the levels of total phenols, flavonoids and ascorbic acid. Liver tissues from goat treated with H₂O₂ (500 μM) showed significantly decreased GSH content by 42.9 % and activities of catalase by 50 % and glutathione reductase by 66.6 %; while increased thiobarbituric acid reactive substances and nitric oxide level by 2.53- and 0.86-fold, respectively, and activity of glutathione S-transferase by 0.96-fold. Grape skin extracts showed the stronger protective activity against H₂O₂-induced oxidative stress in liver tissue ex vivo, than its pulp of any cultivar; and the Flame seedless (black) cultivar showed the highest potential. In conclusion, our study suggested that the higher antioxidant potential, phytochemical contents and significant scavenging capacities in pulp and skin of grape extracts showed the protective action of grape extracts against H₂O₂-induced oxidative stress in liver tissue ex vivo.     

姚桥选煤厂噪音产生原因和治理浅析

阐述了姚桥选煤厂噪音主要来源,从三方面分析了噪音产生的原因,围绕设备选型、围护结构、更换皮带接头、更换安装隔音装置,采用弹性材料方式以达到噪音治理的效果。     

从S2到CPn 的共形极小浸入

通过李群、活动标架,以及调和映射来研究从S2到CPn的共形极小浸入．首先,用一种新方法证明Bolton的一个定理,从S2到的全纯曲线在差一个刚动的情况下由度量唯一决定;其次,利用从 S2到CPn的共形极小浸入来构造从S2到G2,n+1的共形极小浸入;最后,如果φ 是从S2到CPn 的全实共形极小浸入,且φ 是常曲率的,则可以找出具体的等距变换ｇ,使得ｇφ 包含在RPnCPn中．     

三株新型发酵产氢菌的分离和不同发酵条件下产氢性能的比较

氢能是理想的清洁能源,生物制氢技术的研究和开发已成为当前一个研究热点。许多细菌在厌氧条件下发酵复杂的有机化合物,同时产生H2。本文选择了来自同一活性污泥样品的3株有较高产氢能力的发酵细菌,采用生化和电镜技术对其形态学特征进行了观察比较,并进一步比较研究了在不同pH值条件下,它们产氢量、细菌生长量、液相发酵产物组成的变化和差异。获得了三株产氢菌的单位体积培养基最大累积产氢量,提出了纯培养生物制氢的最佳条件,为混合培养生物制氢强化工艺提供参考。     

化学反应动力学

氟原子加氢分子及其同位素分子的反应(F+H2/D2/HD)在化学反应动力学的研究发展中一直扮演着重要的角色。在过去的10年里,科学家们通过精心设计的实验和高精度的理论计算,使得有关该反应体系的态-态动力学研究,特别是对反应机制、过渡态结构及其动力学性质、非绝热效应的认识有了长足的进步,得到了有关F+H2这个教科书式的反应体系动力学行为的结论性的研究成果。     

网络大数据在优化科技期刊选题策划中的应用与实践

【目的】探讨利用中国知网大数据优化科技期刊的选题策划,以提高科技期刊的影响力。【方法】 以《中国实用内科杂志》 “急性胰腺炎的诊治”选题策划为例,介绍该期选题背景、如何利用资源总库文献检索系统中的被引频次和下载频次判断研究热点、利用中国知网的学术趋势搜索模块验证选题策划以及检索功能确定撰稿专家等过程,并分享经验体会。【结果】急性胰腺炎选题刊出后受到了读者及作者的广泛欢迎,大份发行增加了3000册,出售单行本3000份,同时中国知网显示下载量和被引频次增加显著。【结论】《中国知网》大数据对科技期刊编辑了解学科热点、了解学科发展态势和发展方向提供了辅助信息,并为选取合适的约稿专家提供了线索。     

Mineralogy of the deep lower mantle in the presence of H2O

Understanding the mineralogy of the Earth''s interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle (DLM, 1800–2890 km in depth) and observed surprising mineralogical transformations in the presence of water. Ferropericlase, (Mg, Fe)O, which is the most abundant oxide mineral in Earth, reacts with H₂O to form a previously unknown (Mg, Fe)O₂H_x (x ≤ 1) phase. The (Mg, Fe)O₂H_x has a pyrite structure and it coexists with the dominant silicate phases, bridgmanite and post-perovskite. Depending on Mg content and geotherm temperatures, the transformation may occur at 1800 km for (Mg_0.6Fe_0.4)O or beyond 2300 km for (Mg_0.7Fe_0.3)O. The (Mg, Fe)O₂H_x is an oxygen excess phase that stores an excessive amount of oxygen beyond the charge balance of maximum cation valences (Mg²⁺, Fe³⁺ and H⁺). This important phase has a number of far-reaching implications including extreme redox inhomogeneity, deep-oxygen reservoirs in the DLM and an internal source for modulating oxygen in the atmosphere.