Bacteriophage

Abstract

SUMMARY In the lysogenic bacterium the bacterial virus exists as prophage. It is composed of desoxyribosenucleic acid (DNA) and occupies a defined site on the bacterial chromosome. Normally the prophage divides in harmony with the nucleus of the bacterium, so that lysogenesis is hereditary. Occasionally the prophage reverts from symbiosis to virulence, and multiplies at the expense of its host, producing a brood of free phage particles. This is believed to occur when the prophage becomes detached from the chromosome. Free phage particles may be temperate (capable of reproducing lysogenesis in a sensitive bacterium) or virulent (unable to produce lysogenesis and multiplying only at the expense of the doomed host). Temperate particles greatly outnumber virulent particles, which are in fact mutants. Reasons are given for believing that all virulent phages (such as the T series of coliphages) originate in this way. Free phage particles have a characteristic tadpole‐like structure of varying proportions. The tail and the covering of the head are composed of protein, which has specific antigenic characters. The contents of the head consist of DNA. The protein envelope and tail of the particle are chiefly mechanical in function. The tail adheres to the host bacterium and breaches its covering membrane. The contents of the head are then injected into the bacterium. They constitute the infective element. A temperate phage may produce lysogenesis or may multiply in the same way as a virulent particle. Various factors facilitate or interfere with the establishment of lysogenesis. There is evidence to suggest that some temperate particles are specially endowed to produce lysogenesis, while others can undergo only productive development at the expense of the host. Virulent particles multiply only by productive development. The infecting virus displaces the genetic apparatus of the bacterium and directs the bacterial enzymes to its own ends. The nucleic acid of the bacterium, augmented if necessary by newly synthesized material from the culture medium, is broken down to nucleotide level or lower, and resynthesized into viral DNA. Protein is synthesized separately. Ultimately both are assembled into mature particles. Lysogenic bacteria are immune to the phage they produce, and to allied types. Occasional virulent mutants are exceptions to this rule. In certain cases temperate phage particles transduce genetic characters from one bacterium to another. Bacterial species (the classical example being Salmonella typhi) can be broken down into numerous ‘phage‐types’ by tests which exploit the hereditary immunity conferred by the various symbiotic phages. Alternatively, different races of a bacterial species can be recognized by isolating and identifying the symbiotic phage which they carry.

Electron Microscope Observations on Intracellular Virus-Like Particles Associated With the Cells of the Lucké Renal Adenocarcinoma

“…Are the cells of such tumors actually free of virus or is it present in a latent form that at present cannot be identified morphologically? It is generally accepted that virus can persist in a lysogenic strain of colon bacillus through many generations without visible expression, but during this time, it retains the potentiality of producing infectious particles and of destroying its host, when reactivated (23,16,3). Some viruses that produce cancer in animals can likewise exist in a latent condition.…”

A Disease of Grasshoppers Caused by the Bacterium Pseudomonas Aeruginosa (Schroeter) Migula

“…;ccl certain propel-ties. Strains were separable into five phage types on the basis of their possession of or sensitivity to temperate bacteriophages, as defined by BOJ-cl (2). P. aerzlginosa, 10145 of the American Type Culture Collection, was similar to the grasshopper strains but was insensitive to the temperate phages and did not carry a symbiotic phage, to ~vhich grasshopper strains were sensitive.…”

Lysogenicity in Streptomycetes

“…To avoid any misunderstanding, it therefore seems justifiable to begin with a short discussion of what is meant by lysogenicity (for details see the reviews of Lwoff, 1953, Boyd, 1956, and Bertani, 1958.…”