In addition to the expression of recombinant proteins, baculoviruses have been developed as a platform for the display of complex eukaryotic proteins on the surface of virus particles or infected insect cells. Surface display has been used extensively for antigen presentation and targeted gene delivery but is also a candidate for the display of protein libraries for molecular screening. However, although baculovirus gene libraries can be efficiently expressed and displayed on the surface of insect cells, target gene selection is inefficient probably due to super-infection which gives rise to cells expressing more than one protein. In this report baculovirus superinfection of Sf9 cells has been investigated by the use of two recombinant multiple nucleopolyhedrovirus carrying green or red fluorescent proteins under the control of both early and late promoters (vAcBacGFP and vAcBacDsRed). The reporter gene expression was detected 8 hours after the infection of vAcBacGFP and cells in early and late phases of infection could be distinguished by the fluorescence intensity of the expressed protein. Simultaneous infection with vAcBacGFP and vAcBacDsRed viruses each at 0.5 MOI resulted in 80% of infected cells co-expressing the two fluorescent proteins at 48 hours post infection (hpi), and subsequent infection with the two viruses resulted in similar co-infection rate. Most Sf9 cells were re-infectable within the first several hours post infection, but the re-infection rate then decreased to a very low level by 16 hpi. Our data demonstrate that Sf9 cells were easily super-infectable during baculovirus infection, and super-infection could occur simultaneously at the time of the primary infection or subsequently during secondary infection by progeny viruses. The efficiency of super-infection may explain the difficulties of baculovirus display library screening but would benefit the production of complex proteins requiring co-expression of multiple polypeptides.
Both topography and buoyancy can drive groundwater flow; however, the interactions between them are still poorly understood. In this paper, the authors conduct numerical simulations of variable-density fluid flow and heat transport to quantify their relative importance. The finite element modeling experiments on a 2-D conceptual model reveal that the pattern of groundwater flow depends largely upon the relative magnitude of the flow rate due to topography alone and the flow rate due to buoyancy alone. When fluid velocity due to topography is greater than that due to buoyancy at large water table gradients, topography-driven 'forced convection' overwhelms buoyancy-driven 'free convection'. When flow velocity due to buoyancy is greater than that due to topography at small water table gradients, mixed free and forced convection takes place. In this case, free convection becomes dominant, but topography-driven flow still plays an important role since it pushes the free convection cells to migrate laterally in the downhill direction. Consequently, hydrothermal fluid flow remains changing periodically with time and no steady state can be reached. The presence of a low-permeability layer near the surface helps eliminate the topography effect on the underlying free convection. hydrothermal flow, free convection, forced convection, topography, buoyancy, finite element modeling Citation:Yang J W, Feng Z H, Luo X R, et al. Numerically quantifying the relative importance of topography and buoyancy in driving groundwater flow. Sci
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