- Lysogenic cycle
) can release it, causing proliferation of new phages via the lytic cycle. Lysogenic cycles can also occur in eukaryotes, although the method of incorporation of DNA is not fully understood.
Following are some types of viruses that replicate by the lysogenic cycle, but also partly by the lytic cycle.
DNA phages, called temperate phages, only lyse a small fraction of bacterial cells; in the remaining majority of the bacteria, the phage DNA becomes integrated into the bacterial chromosome and replicates along with it. In this lysogenic state, the information contained in the viral nucleic acid is not expressed. The model organism for studying lysogeny is the lambda phage. Roughly 50-60 nucleotides are taken out of the lysogenic pathway and used.
In some interactions between lysogenic phages and bacteria, lysogenic conversion may occur. It is when a temperate
phageinduces a change in the phenotypeof the bacteriainfected that is not part of a usual phage cycle. Changes can often involve the external membrane of the cell by making it impervious to other phages or even by increasing the pathogenic capability of the bacteria for a host.
Corynebacterium diphtheriae" produces the toxin of diphtheriaonly when it is infected by the phage β. In this case, the gene that codes for the toxin is carried by the phage, not the bacteria.
Vibrio cholerae" is a non-toxic strain that can become toxic, producing cholera toxin, when it is infected with the phage CTXφ.
Clostridium botulinum" causes botulism.
Streptococcus pyogenes" causes scarlet fever.
Extra genes present in prophage genomes which do not have a phage function but (may) act as
fitness factorsfor the lysogenare termed "morons". [cite journal |author=Canchaya C, Proux C, Fournous G, Bruttin A, Brüssow H |title=Prophage genomics |journal=Microbiol. Mol. Biol. Rev. |volume=67 |issue=2 |pages=238–76 |year=2003 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=156470 |pmid=12794192 |doi=10.1128/MMBR.67.2.238-276.2003]
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