Prophage

When a temperate phage is mixed with sensitive indicator bacteria and plated as described above, the reaction at each focus of infection is generally a combination of lytic and lysogenic responses. Some bacteria will be lysed and produce phage, others will survive as lysogenic cells, and the plaque becomes visible as a partial area of clearing in the bacterial lawn. It is possible to pick off cells from the central areas of these plaques and demonstrate that they carry prophage. 

The phage lambda (X) ofE. coll is the temperate phage that has been most extensively studied. When any particular strain oiE. coli, say K12, is infected with A, the cells surviving the infection are designated E. coli K 12(A) to indicate that they are carrying the /1-prophage. 

Integration of the prophage into the bacterial ehromosome ensures that, on cell division, each daughter cell will acquire the set of viral genes. 

In a normally growing culture of lysogenic bacteria, the majority of bacteria manage to keep their prophages in a dormant state. In a very small minority of cells, however, the prophage genes express themselves. This results in the multiplieation of the virus, lysis of the cells and liberation of infectious particles into the medium. 

Lysogeny is generally a veiy stable state, but occasionally a cell will lose its prophage and these cured cells are once more susceptible to infection by that particular phage type. 

Lysogeny is an extremely common phenomenon and it seems that most natural isolates of bacteria carry one or more prophages some strains of Staph, aureus have been shown to carry four or five different prophages. 

More recently, the fact that many of the chemical agents whieh eause the induetion of prophage are carcinogenic has led to the use of lysogenie baeteria in sereening tests for deteeting potential carcinogens. 

Studies on the transformahon of tissue cultures with DNA-containing vimses have shown that, although complete vims particles cannot be found in the infected, transformed cells, viral DNA is present and is bound to the transformed cell DNA as provirus, analogous to the prophage of lysogenic bacteria. 

Briaux S, Gerbaud G, Jaffe-Brachet A. 1979. Studies of a plasmid coding for tetracycline resistance and hydrogen sulfide production incompatible with the prophage PI. Mol Gen Genet 170 319-325. 

The temperate virus does not exist in its mature, infectious state inside the cell, but rather in a latent form, called the provirus or prophage state. In considering virulent viruses we learned that the DNA of the virulent virus contains information for the synthesis of a number of enzymes and other proteins essential to virus reproduction. The prophage of the temperate virus carries similar information, but in the lysogenic cell this information remains dormant because the expression of the virus genes is blocked through the action of a specific repressor coded for by the virus. As a result of a genetic switch, the repressor is inactivated, virus reproduction occurs, the cell lyses, and virus particles are released. 

A lysogenic culture can be treated so that most or all of the cells produce virus and lyse. Such treatment, called induction, usually involves the use of agents such as ultraviolet radiation, nitrogen mustards, or X rays, known to damage DNA and activate the SOS system. However, not all prophages are inducible in some temperate viruses, prophage expression occurs only by natural events. 

It is sometimes possible to eliminate the lysogenic virus (to cure the strain) by heavy irradiation or treatment with nitrogen mustards. Among the few survivors may be some cells that have been cured. Presumably the treatment causes the prophage to detach from the host chromosome and be lost during subsequent cell growth. Such a cured strain is no longer immune to the virus and can serve as a suitable host for study of virus replication. 

E. coli WP2S ( ),SR714 X Prophage i nducti on - - Houk and Demari ni 1987... 

Houk VS, DeMarini DM. 1987. Induction of prophage lambda by chlorinated pesticides. Mutat Res 182(4) 193-201. 

MOREAU, P. and DEVORET, R. Potential Carcinogens Tested by Inductions and Mutageneisis of Prophage X in Escherichia coli K12 , in HIATT, H. H., WATSON, J. D. and WINSTEN, J. A. (eds.). Origins of Human Cancer, p. 1451, Cold Springs Harbor Laboratory Publ., Cold Springs Harbor, NY, 1977. 

The evaluation of the aforementioned outbreak seems to be of practical consequence for quality control throughout the food industry. On the basis of the results of this evaluation and on the basis of the knowledge that there are strains of salmonella which owing to the existence of plasmids or prophages are able... 

Prophage induction, SOS repair, DNA strand breaks or cross-links Prophage induction, SOS repair, DNA strand breaks or cross-links Salmonella typhimurium TA1535/pSK1002)... 

There are few data available on the genetic toxicology of 5-chloro-ori/70-toluidine. In single assays, it did not induce mutagenicity in Salmonella typhimurium, prophage lambda in Escherichia coli or unscheduled DNA synthesis in cultured rat hepatocytes. 

DeMarini, D.M. Brooks, H.G. (1992) Induction of prophage lambda by chlorinated organics detection of some single-species/single-site carcinogens. Environ, mol. Mutag., 19, 98-111 Deutsche Forschungsgemeinschaft (1999) List ofMAK and BAT Values 1999 (Report No. 35), Weinheim, Wiley-VCH, pp. 41, 118... 

Glycidol gave a positive response in assays of prophage induction and SOS repair m Escherichia coli. Results were uniformly positive in several Salmonella typhimurium reverse mutation assays and in two fungal mutation assays. The sex-linked recessive lethal mutation assay and the heritable translocation test in Drosophila melanogaster also gave positive results. 

Prophage induetion, SOS repair test, DNA strand breaks, -... 

Rossman TG, Molina M, Meyer L, et al. 1991. Performance of 133 compounds in the lambda prophage induction endpoint of the Microscreen assay and a comparison with IS. typhimurium mutagenicity and rodent carcinogenicity assays. Mutat Res 260 349-367. 

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