virology Virology is the Scientific method, scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host (biology), ...

, temperate refers to the ability of some bacteriophages (notably coliphage λ) to display a

lysogenic life cycle Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction (the lytic cycle being the other). Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formation of a circu ...

. Many (but not all) temperate phages can integrate their

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

s into their host bacterium's chromosome, together becoming a

lysogen A lysogen or lysogenic bacterium is a bacterial cell which can produce and transfer the ability to produce a phage. A prophage is either integrated into the host bacteria's chromosome or more rarely exists as a stable plasmid within the host cell ...

as the phage genome becomes a prophage. A temperate phage is also able to undergo a productive, typically

lytic The lytic cycle ( ) is one of the two cycles of viral reproduction (referring to bacterial viruses or bacteriophages), the other being the lysogenic cycle. The lytic cycle results in the destruction of the infected cell and its membrane. Bacter ...

life cycle, where the prophage is expressed, replicates the phage genome, and produces phage progeny, which then leave the

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. With phage the term

virulent Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...

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).

Induction

At some point, temperate bacteriophages switch from the lysogenic life cycle to the lytic life cycle. This conversion may happen spontaneously, although at very low frequencies (λ displays spontaneous conversion of 10⁻⁸ to 10⁻⁵ per cell). In the majority of observed switch events, stressors - such as the cell's

SOS response The SOS response is a global response to DNA damage in which the cell cycle is arrested and DNA repair and mutagenesis is induced. The system involves the RecA protein ( Rad51 in eukaryotes). The RecA protein, stimulated by single-stranded DNA, ...

(due to DNA damage) or a change in nutrients - induces the switch.

Notes

Virology Bacteriophages {{virus-stub