In situ hydrogen utilization for high fraction acetate production in mixed culture hollow-fiber membrane biofilm reactor

Syngas fermentation is a promising route for resource recovery. Acetate is an important industrial chemical product and also an attractive precursor for liquid biofuels production. This study demonstrated high fraction acetate production from syngas (H₂ and CO₂) in a hollow-fiber membrane biofilm reactor, in which the hydrogen utilizing efficiency reached 100 % during the operational period. The maximum concentration of acetate in batch mode was 12.5 g/L, while the acetate concentration in continuous mode with a hydraulic retention time of 9 days was 3.6?±?0.1 g/L. Since butyrate concentration was rather low and below 0.1 g/L, the acetate fraction was higher than 99 % in both batch and continuous modes. Microbial community analysis showed that the biofilm was dominated by Clostridium spp., such as Clostridium ljungdahlii and Clostridium drakei, the percentage of which was 70.5 %. This study demonstrates a potential technology for the in situ utilization of syngas and valuable chemical production.     

Different utilizable substrates have different effects on cometabolic fate of imidacloprid in Stenotrophomonas maltophilia

Imidacloprid, the largest selling insecticide in the world, is more stable in soil, and its environmental residue and effects are attracting people's close attention. One of imidacloprid metabolism pathways was degraded to CO₂ through olefin imidacloprid pathway. Here, we report that sucrose as a utilizable substrate enhanced the cometabolism of imidacloprid by Stenotrophomonas maltophilia CGMCC 1.1788 to produce 5-hydroxy imidacloprid, whereas when succinate was used as a utilizable substrate, 5-hydroxy imidacloprid from imidacloprid was transformed to olefin imidacloprid, and the latter was further degraded. The hydroxylation of imidacloprid required NAD(P)H, whereas the dehydration of 5-hydroxy imidacloprid to form olefin imidacloprid required succinate rather than NAD(P)H. NADPH greatly favored the hydroxylation of imidacloprid more than NADH, and NADPH inhibited the dehydration of 5-hydroxy imidacloprid to olefin imidacloprid, but NADH did not. Therefore, sucrose may be metabolized through hexose monophosphate pathway to produce mainly NADPH which participated in the hydroxylation of imidacloprid to 5-hydroxy imidacloprid and meanwhile inhibited the dehydration of 5-hydroxy imidacloprid to olefin imidacloprid, whereas succinate may be metabolized mainly through the tricarboxylic acid cycle to produce NADH which was involved in hydroxylation of imidacloprid to 5-hydroxy imidacloprid but did not inhibit the dehydration of 5-hydroxy imidacloprid to olefin imidacloprid. Our results have a significant meaning in further understanding the influence of different utilizable substrates on the cometabolic pathways and the fate of environmental imidacloprid.     

Comparison of membrane electroporation and protein denature in response to pulsed electric field with different durations

In this paper, we compared the minimum potential differences in the electroporation of membrane lipid bilayers and the denaturation of membrane proteins in response to an intensive pulsed electric field with various pulse durations. Single skeletal muscle fibers were exposed to a pulsed external electric field. The field‐induced changes in the membrane integrity (leakage current) and the Na channel currents were monitored to identify the minimum electric field needed to damage the membrane lipid bilayer and the membrane proteins, respectively. We found that in response to a relatively long pulsed electric shock (longer than the membrane intrinsic time constant), a lower membrane potential was needed to electroporate the cell membrane than for denaturing the membrane proteins, while for a short pulse a higher membrane potential was needed. In other words, phospholipid bilayers are more sensitive to the electric field than the membrane proteins for a long pulsed shock, while for a short pulse the proteins become more vulnerable. We can predict that for a short or ultrashort pulsed electric shock, the minimum membrane potential required to start to denature the protein functions in the cell plasma membrane is lower than that which starts to reduce the membrane integrity. Bioelectromagnetics 34:253–263, 2013. © 2012 Wiley Periodicals, Inc.     

基于EMA-qPCR的茄科青枯菌活体检测技术的建立

【目的】利用特异性核酸染料叠氮溴乙锭(Ethidium monoazide bromide, EMA)与实时荧光定量PCR技术相结合, 建立一种能有效区分青枯菌死活细胞的检测方法。【方法】样品DNA制备前经EMA渗透预处理, 再进行实时荧光定量PCR特异扩增菌体DNA。【结果】终浓度为2.0 mg/L的EMA能有效排除1.0×107 CFU/mL灭活青枯菌细胞DNA的扩增, 对活细胞和不可培养状态(Viable but non-culturable, VBNC)活菌的DNA扩增均没有影响。当每个定量PCR反应体系中的活细胞在5.0×100?5.0×104 CFU范围内时, 扩增Ct值与定量PCR反应体系中活细胞CFU对数值呈良好的负相关性(R2=0.992 5)。比较EMA-qPCR法和平板计数法对经过不同温度短期保存的青枯菌检测结果发现, 待检样品可在24 °C与4 °C冷藏条件下短期保存。【结论】本研究建立的EMA-qPCR方法能有效检测青枯菌VBNC细胞和有效区分死活菌, 避免或减少青枯菌PCR检测的假阳性和假阴性。     

Clipping of Flexible Tails of Histones H3 and H4 Affects the Structure and?Dynamics of the Nucleosome

Förster resonance energy transfer was used to monitor the dynamic conformations of mononucleosomes under different chromatin folding conditions to elucidate the role of the flexible N-terminal regions of H3 and H4 histones. The H3 tail was shown to partake in intranucleosomal interactions by restricting the DNA breathing motion and compacting the nucleosome. The H3 tail effects were mostly independent of the ionic strength and valency of the ions. The H4 tail was shown to not greatly affect the nucleosome conformation, but did slightly influence the relative population of the preferred conformation. The role of the H4 tail varied depending on the valency and ionic strength, suggesting that electrostatic forces play a primary role in H4 tail interactions. Interestingly, despite the H4 tail’s lack of influence, when H3 and H4 tails were simultaneously clipped, a more dramatic effect was seen than when only H3 or H4 tails were clipped. The combinatorial effect of H3 and H4 tail truncation suggests a potential mechanism by which various combinations of histone tail modifications can be used to control accessibility of DNA-binding proteins to nucleosomal DNA.     

Single-Molecule Force Spectroscopy Study on the Mechanism of RNA Disassembly in Tobacco Mosaic Virus

To explore the disassembly mechanism of tobacco mosaic virus (TMV), a model system for virus study, during infection, we have used single-molecule force spectroscopy to mimic and follow the process of RNA disassembly from the protein coat of TMV by the replisome (molecular motor) in vivo, under different pH and Ca²⁺ concentrations. Dynamic force spectroscopy revealed the unbinding free-energy landscapes as that at pH 4.7 the disassembly process is dominated by one free-energy barrier, whereas at pH 7.0 the process is dominated by one barrier and that there exists a second barrier. The additional free-energy barrier at longer distance has been attributed to the hindrance of disordered loops within the inner channel of TMV, and the biological function of those protein loops was discussed. The combination of pH increase and Ca²⁺ concentration drop could weaken RNA-protein interactions so much that the molecular motor replisome would be able to pull and disassemble the rest of the genetic RNA from the protein coat in vivo. All these facts provide supporting evidence at the single-molecule level, to our knowledge for the first time, for the cotranslational disassembly mechanism during TMV infection under physiological conditions.