Purification and Protein Composition of PM2, the First Lipid-Containing Bacterial Virus To Be Isolated

Abstract

The marine, icosahedral bacteriophage PM2 was isolated in the late 1960s. It was the first phage for which lipids were firmly demonstrated to be part of the virion structure and it has been classified as the type organism of the Corticoviridae family. The host, Pseudoalteromonas espejiana BAL-31, belongs to a common group of marine bacteria. We developed a purification method producing virions with specific infectivity approximately as high as that of the lipid-containing phages PRD1 and φ6. The sensitivity of the virus to normally used purification media such as those containing sucrose is demonstrated. We also present an alternative host, a pseudoalteromonad, that allows enhanced purification of the virus under reduced salt conditions. We show, using N-terminal amino acid sequencing and comparison with the genomic sequence, that there are at least eight structural proteins in the infectious virus.

Genomics of Bacterial and Archaeal Viruses: Dynamics within the Prokaryotic Virosphere

“…PM2 infects marine Pseudoalteromonas species (57,135) and is currently the sole assigned member of the Corticoviridae (11). The virus is strictly virulent under laboratory conditions; at the end of the infection cycle, the host cells are disrupted via a mechanism which differs considerably from those described for other dsDNA bacteriophages, including tectivirus PRD1 (146,147).…”

Bacteriophage PM2 Has a Protein Capsid Surrounding a Spherical Proteinaceous Lipid Core

“…P1, with a molecular mass of 37.5 kDa, has been identified as the spike protein located at the fivefold vertices, and P2, with a molecular mass of 30.2 kDa, is the major capsid protein. Proteins P3 and P4 are located internally (9,10,22,36,37,38,41,45,46), and P4 has been proposed to be an integral membrane protein interacting with the viral DNA (9,40,42). Dissociation of the PM2 particle has been extensively studied.…”

“…strain BAL-31), isolated along with the virus (25,32), and Pseudoalteromonas sp. strain ER72M2, obtained from the East River, New York, by Leonard Mindich (38). Originally, considerable interest was directed toward this virus system (about 200 references), but since 1983, only a few studies have been published.…”

“…Originally, considerable interest was directed toward this virus system (about 200 references), but since 1983, only a few studies have been published. Recently, we decided to examine this virus system (38,39), as our laboratory is focused on lipid-containing bacterial viruses.…”

“…The average diameter of the icosahedral particle is ϳ60 nm (24,34,49), and the lipids are located internally (15,34). The sedimentation coefficient (s 20 , w ) of the particle is 293S, and buoyant densities in sucrose and cesium chloride are 1.26 and 1.28 g/cm 3 , respectively (16,38). The stability of the virion is strongly dependent on sodium and especially on calcium ions, and the virion equilibrated in sucrose is inactive (38).…”