Characterization of heterologous and native enzyme activity profiles in metabolically engineered Zymomonas mobilis strains during batch fermentation of glucose and xylose mixtures

Zymomonas mobilis has been metabolically engineered to broaden its substrate utilization range to include d-xylose and l-arabinose. Both genomically integrated and plasmid-bearing Z. mobilis strains that are capable of fermenting the pentose d-xylose have been created by incorporating four genes: two genes encoding xylose utilization metabolic enzymes (xylA/xylB) and two genes encoding pentose phosphate pathway enzymes (talB/tktA). We have characterized the activities of the four newly introduced enzymes for xylose metabolism, along with those of three native glycolytic enzymes, in two different xylose-fermenting Z. mobilis strains. These strains were grown on glucose-xylose mixtures in computer-controlled fermentors. Samples were collected and analyzed to determine extracellular metabolite concentrations as well as the activities of several intracellular enzymes in the xylose and glucose uptake and catabolism pathways. These measurements provide new insights on the possible bottlenecks in the engineered metabolic pathways and suggest methods for further improving the efficiency of xylose fermentation.     

Anaerobic treatment of animal byproducts from slaughterhouses at laboratory and pilot scale

Different mixtures of animal byproducts, other slaughterhouse waste (i.e., rumen, stomach and intestinal content), food waste, and liquid manure were codigested at mesophilic conditions (37°C) at laboratory and pilot scale. Animal byproducts, including blood, represent 70–80% of the total biogas potential from waste generated during slaughter of animals. The total biogas potential from waste generated during slaughter is about 1300 MJ/cattle and about 140 MI/pig. Fed-batch digestion of pasteurized (70°C, 1h) animal byproducts resulted in a fourfold increase in biogas yield (1.14L/g of volatile solids [VS]) compared with nonpasteurized animal bypproducts (0.31L/g of VS). Mixtures with animal byproducts representing 19–38% of the total dry matter were digested in continuous-flow stirred tank reactors at laboratory and pilot scale. Stable processes at organic loading rates (OLRs) exceeding 2.5g of VS/(L·d) and hydraulic retention times (HRTs) less than 40 d could be obtained with total ammonia nitrogen concentrations (NH₄−N+NH₃−N) in the range of 4.0–5.0 g/L. After operating one process for more than 1.5 yr at total ammonia nitrogen concentrations >4 g/L, an increase in OLR to 5 g of VS/(L·d) and a decrease in HRT to 22 d was possible without accumulation of volatile fatty acids.     

rGO/TiO2及其三元复合材料光催化性能的研究进展

rGO/TiO2复合材料优异的光催化性能为其在有机染料降解,雨水消毒和催化析氢等方面的应用提供可能,通过与金属、金属化合物或高聚物复合可提升光催化效率和化学稳定性.分析反应机理,阐述现阶段研究的重点和不足,同时对未来发展和应用进行展望.     

A convenient method to remove ruthenium byproducts from olefin metathesis reactions using polymer-bound triphenylphosphine oxide (TPPO)

Summary Ruthenium byproducts from ring-closing metathesis reactions can be removed by refluxing the crude reaction mixture with resin-bound triphenylphosphine oxide (TPPO) in toluene or by stirring with dimethyl sulfoxide (DMSO) and silica gel at room temperature. Residual levels of ruthenium can be achieved that are as low as 0.04 μg per 5 mg of product when a combination of TPPO, DMSO, and silica gel is used. The polymer-bound TPPO retained its efficiency after being recycled six times.     

Effect of quenching time and quenching agent dose on total organic halogen measurement

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX measurement involves concentration of halogenated organic DBPs by adsorption onto activated carbon. Prior to activated carbon adsorption, quenching the chlorine residual in a water sample is an indispensable step to eliminate the positive interference resulting from continued chlorination with organic compounds adsorbed on the activated carbon surface or with the activated carbon surface itself. Arsenite is generally applied as the quenching agent. In this study, the arsenite quenching agent dose that was 100% of the stoichiometric amount of the chlorine residual in a water sample was demonstrated to be most appropriate. In practice, to ensure complete reduction of chlorine residual, slight overdose of arsenite is often recommended, but this was found to cause negative interferences in the TOX measurement due to two reasons. First, the competitive adsorption existed between halogenated organic DBPs and the excessive arsenite on the activated carbon. This competitive adsorption effect was pronounced within a quenching time of 15?min. After 15?min of quenching, a large fraction of arsenite might have reacted with some easily-reduced halogenated DBPs to become arsenate, which is partially ionized at pH 2 and less likely adsorbed on the activated carbon. In this case, more halogenated organic DBPs could be adsorbed on the activated carbon, resulting in the measured TOX concentrations to be much closer to the actual one contained in the sample. Second, excessive arsenite might lead to reduction or decomposition of halogenated organic DBPs with a prolonged quenching time (>60?min). Thus, to avoid the negative interferences, the appropriate quenching time should be 15–60?min.     

Effect of acoustic frequency and power density on the aqueous ultrasonic-assisted extraction of grape pomace (Vitis vinifera L.) – A response surface approach

Aqueous ultrasound-assisted extraction (UAE) of grape pomace was investigated by Response Surface Methodology (RSM) to evaluate the effect of acoustic frequency (40, 80, 120 kHz), ultrasonic power density (50, 100, 150 W/L) and extraction time (5, 15, 25 min) on total phenolics, total flavonols and antioxidant capacity. All the process variables showed a significant effect on the aqueous UAE of grape pomace (p < 0.05). The Box–Behnken Design (BBD) generated satisfactory mathematical models which accurately explain the behavior of the system; allowing to predict both the extraction yield of phenolic and flavonol compounds, and also the antioxidant capacity of the grape pomace extracts. The optimal UAE conditions for all response factors were a frequency of 40 kHz, a power density of 150 W/L and 25 min of extraction time. Under these conditions, the aqueous UAE would achieve a maximum of 32.31 mg GA/100 g fw for total phenolics and 2.04 mg quercetin/100 g fw for total flavonols. Regarding the antioxidant capacity, the maximum predicted values were 53.47 and 43.66 mg Trolox/100 g fw for CUPRAC and FRAP assays, respectively. When comparing with organic UAE, in the present research, from 12% to 38% of total phenolic bibliographic values were obtained, but using only water as the extraction solvent, and applying lower temperatures and shorter extraction times. To the best of the authors’ knowledge, no studies specifically addressing the optimization of both acoustic frequency and power density during aqueous-UAE of plant materials have been previously published.     

非水毛细管电泳法同时测定消毒剂、个人护理品及药膏中三氯生、三氯卡班和对氯间二甲苯酚

三氯生（TCS）、三氯卡班（TCC）和对氯间二甲苯酚（PCMX）这3种消毒有效成分因广谱杀菌而广泛应用于消毒剂、个人护理品及药品中。为监督这些产品质量、保障消毒效果,非常有必要建立同时分析这3种消毒有效成分的方法。鉴于此,该文以十二烷基三甲基溴化铵（DTAB）为电渗流反转剂,建立了同时测定上述3种消毒有效成分的非水毛细管电泳-紫外检测新方法,并对分离缓冲体系及浓度、样品介质等条件进行了优化。结果表明,未涂层熔融石英毛细管（20.0 cm×50.0 μm,总长度30.2 cm）为分离毛细管,14 mmol/L硼砂、2 g/L聚乙二醇20000和0.5 mmol/L DTAB的甲醇溶液为分离缓冲溶液,样品介质为含5 g/L聚乙二醇20000的甲醇-乙腈（50∶50, v/v）,在214 nm下进行检测,实现了3种消毒有效成分的同时分离。在1~100 mg/L范围内,3种消毒有效成分的校正峰面积与质量浓度呈良好的线性关系,相关系数（r）均大于0.99。方法的检出限（LOD,信噪比为3）为0.2 mg/L,定量限（LOQ,信噪比为10）为1.0 mg/L;加标回收率在94.5%~104.4%范围内,相对标准偏差均小于4.8%。利用研究建立的新方法测定了消毒液、洗手液、婴儿爽身粉、抑菌乳膏共31件样品,并将结果与国家标准方法GB/T 27947-2020和GB/T 34856-2017中的液相色谱法结果相比较,无统计学显著性差异。与国标方法相比,方法极大地减少了有机溶剂消耗量。该法前处理简单,结果准确,非常适合实验室的常规分析。     

Sorption and desorption of organic matter on solid‐phase extraction media to isolate and identify N‐nitrosodimethylamine precursors

#x02010;Nitrosodimethylamine is mutagenic in rodents, a drinking water contaminant, and a byproduct of drinking water disinfection by chloramination. Nitrosodimethylamine precursor identification leads to their control and improved understanding of nitrosodimethylamine formation during chloramination. Mass balances on nitrosodimethylamine precursors were evaluated across solid‐phase extraction cartridges and in eluates to select the best combination of solid‐phase media and eluent that maximized recovery of nitrosodimethylamine precursors into a solvent amenable to time‐of‐flight mass spectrometry analysis. After reviewing literature and comparing various solid‐phase cartridges and eluent combinations, a method was obtained to efficiently recover nitrosodimethylamine precursors. The approach with the greatest recoveries of nitrosodimethylamine precursors involved cation exchange resin loaded with water samples at pH 3 and eluted with 5% NH₄OH in methanol. This indicated that nitrosodimethylamine precursors are amines that protonate at low pH and deprotonate at high pH. Quaternary amines were irreversibly sorbed to the cation exchange cartridge and did not account for a large fraction of precursors. Overall, a median recovery of 82% for nitrosodimethylamine precursors was achieved from 11 surface waters and one wastewater. Applying this method allowed discovery of methadone as a new nitrosodimethylamine precursor in wastewater effluent and drinking water treatment plant intakes.     

Potential uses of ultrasound in the biological decontamination of water

In the past there was a prevailing feeling in industry that power ultrasound would be too expensive to use for water treatment on an industrial scale. This was based on calculations involving the direct scale up of power consumption in small-scale (generally batch) laboratory experiments. In recent times this attitude has changed somewhat as a result of the installation of a number of ultrasonic devices in operational water or sewage treatment plants. In our laboratories we have investigated the decontamination of water under the influence of ultrasound alone and in conjunction with other treatments. The results, particularly when applied to flowing systems, indicate a real future for sonochemistry in water treatment.