Active Diffusion of Adsorbed Mycoplasmal Virus L3 on Acholeplasma laidlawii Cell Membranes

Abstract

Mycoplasmas are wall-less prokaryotes. Since tail structures of complex bacteriophages are assumed to function in the penetration of bacterial cell walls, the reported infection of mycoplasmal cells by tailed viruses is most interesting [1, 2]. One of these viruses, mycoplasmal virus L3 (MVL3), is a polyhedral particle ~60 nm in diameter; it has a short tail ~10 nm in diameter and 20 nm long and contains linear double-stranded DNA with a molecular weight of ~26 x 106 [3]. Tail fibers have been described, but their exact number and length are still unknown. Although infection with this virus is lethal for the host cell, the infectious cycle is nonlytic [3]. Studies by electron microscopy have shown several types of interaction between MVL3 and the cell membrane of the host, Acholeplasma laidlawii, during the infectious cycle [7]. (1) Adsorbed virions are found in caps or clusters on the mycoplasmal cell membrane. Such viral capping represents a temperature-sensitive surface redistribution of virus adsorbed to cell receptors. Viruses randomly adsorbed at 4 C redistribute into clusters when the temperature is raised to 37 C. (2) Progeny virions are aligned radially at the membrane with tails oriented towards the membrane. (3) Some extracellular virions are found in small vesicles, so that the particle appears to be enveloped. In addition, large vesicles that contain