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UnlabelledLipid-enveloped viruses replicate and bud from the host cell where they acquire their lipid coat. Ebola virus, which buds from the plasma membrane of the host cell, causes viral hemorrhagic fever and has a high fatality rate. To date, little has been known about how budding and egress of Ebola virus are mediated at the plasma membrane. We have found that the lipid phosphatidylserine (PS) regulates the assembly of Ebola virus matrix protein VP40. VP40 binds PS-containing membranes with nanomolar affinity, and binding of PS regulates VP40 localization and oligomerization on the plasma membrane inner leaflet. Further, alteration of PS levels in mammalian cells inhibits assembly and egress of VP40. Notably, interactions of VP40 with the plasma membrane induced exposure of PS on the outer leaflet of the plasma membrane at sites of egress, whereas PS is typically found only on the inner leaflet. Taking the data together, we present a model accounting for the role of plasma membrane PS in assembly of Ebola virus-like particles.ImportanceThe lipid-enveloped Ebola virus causes severe infection with a high mortality rate and currently lacks FDA-approved therapeutics or vaccines. Ebola virus harbors just seven genes in its genome, and there is a critical requirement for acquisition of its lipid envelope from the plasma membrane of the human cell that it infects during the replication process. There is, however, a dearth of information available on the required contents of this envelope for egress and subsequent attachment and entry. Here we demonstrate that plasma membrane phosphatidylserine is critical for Ebola virus budding from the host cell plasma membrane. This report, to our knowledge, is the first to highlight the role of lipids in human cell membranes in the Ebola virus replication cycle and draws a clear link between selective binding and transport of a lipid across the membrane of the human cell and use of that lipid for subsequent viral entry.

The Integrated, Section Surface Difference Over Time, version 2 (ISSDOTv2) method provides a means of quantifying bedload in large sandbed rivers. Like all measurements, it is important to understand the uncertainty associated with the method before making management decisions based on its results. A methodology is presented for quantifying and combining the uncertainty for each component of the ISSDOTv2 method including particle density, bed porosity, acoustically measured bed topography, the timing of measurements, sand wave identification, and regression analysis used for geometric correction of bedload measurements. The approach provides an indication of the relative magnitude of each source of uncertainty in addition to the uncertainty in the final resultant transport rate. Laboratory flume measurements were used to evaluate the uncertainty limits and verify the approach. The greatest contributor to uncertainty was found to be the bathymetric uncertainty, and, at the highest transport rates, cumulative relative uncertainty was found to be approximately 10%. Cumulative relative uncertainties grew rapidly with decreasing flow rates, driven primarily by the higher relative contribution of the effect of bathymetric uncertainty on the smaller bedforms that are typically present at lower transport rates. The approach documented here will be transferrable to real-world systems to determine the uncertainty in measured bedload sediment transport rates using the ISSDOTv2 method. [ABSTRACT FROM AUTHOR]

The movement of bed forms (sand dunes) in large sand-bed rivers is being used to determine the transport rate of bed load. The ISSDOTv2 (Integrated Section Surface Difference Over Time version 2) methodology uses time sequenced differences of measured bathymetric surfaces to compute the bed-load transport rate. The method was verified using flume studies [1]. In general, the method provides very consistent and repeatable results, and also shows very good fidelity with most other measurement techniques. Over the last 7 years we have measured, computed and compiled what we believe to be the most extensive data set anywhere of bed-load measurements on large, sand bed rivers. Most of the measurements have been taken on the Mississippi, Missouri, Ohio and Snake Rivers in the United States. For cases where multiple measurements were made at varying flow rates, bed-load rating curves have been produced. This paper will provide references for the methodology, but is intended more to discuss the measurements, the resulting data sets, and current and potential uses for the bed-load data.