Virions are one kind of nanoscale pathogen and are able to infect living cells of animals, plants, and bacteria. The infection is an intrinsic property of the virions, and the biological process provides a good model for studying how these nanoparticles enter into cells. During the infection, the viruses employ different strategies to which the cells have developed respective responses. For this paper, we chose Bombyx mori cypovirus 1 (BmCPV-1) interactions with midgut cells from silkworm, and severe acute respiratory syndrome (SARS) associated coronavirus interactions with Vero E6 cells, as examples to demonstrate the response of eukaryotic cells to two different types of virus from our previous studies. The bacteriophage-bacteria interactions are also introduced to elucidate how the bacteriophage conquers the barrier of cell walls in the prokaryotic cells to transport genome into the host. 1. Introduction A virus (including bacteriophages) is an infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria. The size of spherical virus usually ranges from ten nanometers to hundreds of nanometers in diameter. So they can be viewed as one kind of natural nanobiomaterial [1, 2]. A virus consists of single- or double-stranded nucleic acid and a protein shell, called a capsid. Some viruses also have an outer envelope composed of fatty materials (lipids) and proteins. The nucleic acid carries the virus’s genome—its collection of genes—and may consist of either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). The protein capsid provides protection for the nucleic acid and may contain enzymes that enable the virus to enter its appropriate host cell. The host cells of viruses range from animals, plants, fungi, to bacteria and could be divided into two types: the eukaryotic cells and the prokaryotic cells. Transmission electron microscopy (TEM) is a powerful tool to investigate microorganisms and has long been used in the discovery and description of viruses [3]. With appropriate sample preparation and application on a grid, the visual look of virions can be directly obtained. Beside traditional electron microscopy techniques such as negative staining, ultrathin sectioning, and immunoelectron microscopy [4], the relatively recently developed techniques such as cryoelectron microscopy (Cryo-EM) with single particle analysis that provides a new set of methods to investigate the 3D atomic resolution structures of macromolecules and cryo-electron tomography (CryoET) that allows the visualization of
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