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SummaryShigella species possess a type III secretion system (T3SS), which is required for human infection and that delivers effector proteins into target host cells. Here, we show that the effector, IpaH4.5 dampens the pro-inflammatory cytokine response. In both the Sereny test and a murine lung infection model, the Shigella DipaH4.5 mutant strain caused more severe inflammatory responses and significantly induced higher pro-inflammatory cytokine levels (MIP-2 and TNF-a) in the lung homogenates of wild type-infected mice. Moreover, there was a threefold decrease in bacterial colonization of the mutant compared with the WT and DipaH4.5/ ipaH4.5-rescued strains. Yeast two-hybrid screening showed that IpaH4.5 specifically interacts with the p65 subunit of NF-kB. Ten truncated versions of IpaH4.5 and p65 spanning different regions were constructed and expressed to further map the IpaH binding sites with p65. The results revealed that the p65 region spanning amino acids 1-190 of p65 interacted with the IpaH4.5/1-293 N-terminal region. In vitro, IpaH4.5 displayed ubiquitin ligase activity towards ubiquitin and p65. Furthermore, the transcriptional activity of NF-kB was shown to be inhibited by IpaH4.5 utilizing a dual-luciferase reporter gene detection system containing NF-kB promoter response elements. Thus, we conclude that the IpaH4.5 protein is an E3 ubiquitin ligase capable of directly regulating the host inflammatory response by inhibiting the NF-kB signalling pathway.

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The knowledge of adsorption behaviors and mechanism of CO2/CH4 in organic matter is of great importance for CO2 geological sequestration with enhanced gas recovery in shale reservoirs. In this study, the adsorption behaviors and confinement effects of CO2/CH4 in realistic kerogen nanopores have been investigated by using the grand canonical Monte Carlo method. To represent realistic nanopores in the kerogen matrix, the inkbottle-shaped and slit-like nanopores were developed. The effects of temperature, pressure, and pore size on competitive adsorption behaviors and adsorption mechanism of CO2/CH4 were explored. Simulation results indicate that the adsorption capacity of CH4 is lower than that of CO2 in the kerogen matrix with/without kerogen nanopores. A higher pressure and lower temperature are favorable for the adsorption capacities of CO2 and CH4. The gas adsorption capacities have been enhanced in both the inkbottle-shaped and slit-like nanopores. Meanwhile, the existence of inkbottle-shaped micropores is favorable for improving the selectivity of CO2/CH4 in shale organic matter. A higher CO2 injection pressure could improve its adsorption capacity but lower the adsorption selectivity of CO2 over CH4. Furthermore, confinement effects were observed in inkbottle-shaped and slit-like kerogen micropores and small mesopores. Two major factors, including the supercritical state of gas and microscale pores, could enhance the confinement effects. In addition to monolayer adsorption, micropore filling was observed in inkbottle-shaped and slit-like kerogen nanopores because of the confinement effects. It is expected that these results could help in understanding the microscopic adsorption mechanism and provide fundamental information for shale gas exploitation and CO2 sequestration.

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The adsorption behavior and the mechanism of a CO2/CH4 mixture in shale organic matter play significant roles to predict the carbon dioxide sequestration with enhanced gas recovery (CS-EGR) in shale reservoirs. In the present work, the adsorption performance and the mechanism of a CO2/CH4 binary mixture in realistic shale kerogen were explored by employing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. Specifically, the effects of shale organic type and maturity, temperature, pressure, and moisture content on pure CH4 and the competitive adsorption performance of a CO2/CH4 mixture were investigated. It was found that pressure and temperature have a significant influence on both the adsorption capacity and the selectivity of CO2/CH4. The simulated results also show that the adsorption capacities of CO2/CH4 increase with the maturity level of kerogen. Type II-D kerogen exhibits an obvious superiority in the adsorption capacity of CH4 and CO2 compared with other type II kerogen. In addition, the adsorption capacities of CO2 and CH4 are significantly suppressed in moist kerogen due to the strong adsorption strength of H2O molecules on the kerogen surface. Furthermore, to characterize realistic kerogen pore structure, a slit-like kerogen nanopore was constructed. It was observed that the kerogen nanopore plays an important role in determining the potential of CO2 subsurface sequestration in shale reservoirs. With the increase in nanopore size, a transition of the dominated gas adsorption mechanism from micropore filling to monolayer adsorption on the surface due to confinement effects was found. The results obtained in this study could be helpful to estimate original gas-in-place and evaluate carbon dioxide sequestration capacity in a shale matrix.

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