Lysogenic, inducible

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. 

Figure 5.21 Consequences of infection by a temperate bacteriophage. The alternatives upon infection are integration of the virus DNA into the host DNA (lysogenization) or replication and release of mature virus (lysis). The lysogenic cell can also be induced to produce mature virus and lyse.

In Chapter 5, it is concluded that release of intracellular bacterial metabolites after cell lysis may have been responsible for fhe increases in advanced Maillard products. Lysis of bacteria can deliberately be induced by, for example, lysogenic enzymes and phages. In addifion fo fhe direcf targeting of cariogenic microorganisms, lysis could thus contribute indirectly to caries arrestment by causing an extensive Maillard reaction. However, the problem of the concomitant unaesthetic discoloration will need to be considered before practical application becomes feasible. 

Pyrolysis products were also found to induce prophage X in lysogenic E. ooli K12, strain GY5027 (30), by Inductest III, which was developed by Moreau et al, (31) (Figure 2). The genotoxic effects of pyrolysis products on cultured mammalian cells were also investigated. Trp-P-1, Trp-P-2, IQ and MelQ were found to induce diphtheria toxin-resistant mutants of Chinese hamster lung cells in the presence of S9 mix. The mutation frequencies were 33, 160, 40 and 38 per 106 survivors per Mg of Trp-P-1, Trp-P-2,... 

A wide variety of E coli strains designed for protein expression are commercially available, derived from the E. coli strain BL21, that are tailored to facilitate disulfide bond formation, fine-tune protein expression levels, enhance the expression of proteins that contain rare codons, and other specific requirements. These strains are available as lambda DE3 lysogens, which carry a chromosomal copy of the T7 RNA polymerase gene under control of the lac promoter (inducible by IPTG). Once induced, the T7 RNA polymerase drives expression of genes that are under control of the T7 promoter, such as those cloned into the pET family of expres-... 

It should be pointed out here that all the platinum complexes which are active anticancer agents are also efficient inducers. Those complexes which are not active, do not cause lysis. So far, there is a complete isomorphism between the set of active anticancer complexes and the set of efficient inducers. Earlier, we had believed that a good correlation existed between anticancer active complexes and the filament-forming complexes. After a while, however, exceptions in both classes occurred which decreased our faith in this correlation. The correlation of lytic induction and anticancer activity has held up well. In fact, when R. Adamson at the National Cancer Institute reported the anticancer activity of gallium salts, we tested these and, indeed, they did induce lysis in lysogenic bacteria. 

Finally, another potential interplay between UVR and viruses occurs when they coexist with their host in a type of mutualistic relationship, where the nucleic acid of the virus is integrated in the genome of the host and is replicated with it (lysogenic state). Ultraviolet C radiation produced by germicidal lamps (max. at 254 nm) has normally been used, among other stressors, to induce the shift from lysogenic to lytic state in a complex mechanism involving the DNA repair SOS system of the host [93]. However, natural or simulated solar UVR seems not to be very efficient in this process [94,95]. 

The minimum concentration of lavendamycin (0.003 /Ag/ml) required to induce bacteriophage production in the lysogenic strain of Escherichia coli W1709 was found to be comparable to that of streptonigrin (0.008 pg/ ml) (57). 

Induction of Lysogeny. As outlined, the growth of phage from lysogenic bacteria is induced by agents which interact with DNA. 

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