In VIROLOGY , TEMPERATE refers to the ability of some bacteriophages (notably coliphage λ ) to display a lysogenic life cycle . Many (but not all) temperate phages can integrate their genomes into their host bacterium\'s chromosome, together becoming a lysogen as the phage genome becomes a prophage . A temperate phage is also able to undergo a productive, typically lytic life cycle, where the prophage is expressed, replicates the phage genome, and produces phage progeny, which then leave the bacterium . With phage the term virulent is often used as an antonym to temperate, but more strictly a virulent phage is one that has lost its ability to display lysogeny through mutation rather than a phage lineage with no genetic potential to ever display lysogeny (which more properly would be described as an obligately lytic phage).
* ^ Barksdale, L., and S. B. Ardon. 1974. Persisting bacteriophage infections, lysogeny, and phage conversions. Annu. Rev. Microbiol. 28:265-299.
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