Question: How can bacteriophages be characterized?
About the article "Bacteria", section "Bacteriophages".

Candidate passages:
Bacteriophages are viruses that infect bacteria and archaea.
The International Committee on Taxonomy of Viruses officially recognises 28 genera of bacteriophages that belong to 11 families.
They are important in marine ecology: as the infected bacteria burst, carbon compounds are released back into the environment, which stimulates fresh organic growth.
Bacteriophages are useful in scientific research because they are harmless to humans and can be studied easily.
These viruses can be a problem in industries that produce food and drugs by fermentation and depend on healthy bacteria.
Some bacterial infections are becoming difficult to control with antibiotics, so there is a growing interest in the use of bacteriophages to treat infections in humans. 
Experimental evolution studies are a means of testing evolutionary theory under carefully designed, reproducible experiments.
Although theoretically any organism could be used for experimental evolution studies, those with rapid generation times, high mutation rates, large population sizes, and small sizes increase the feasibility of experimental studies in a laboratory context.
For these reasons, bacteriophages (i.e.
viruses that infect bacteria) are especially favored by experimental evolutionary biologists.
Bacteriophages, and microbial organisms, can be frozen in stasis, facilitating comparison of evolved strains to ancestors.
Additionally, microbes are especially labile from a molecular biologic perspective.
Many molecular tools have been developed to manipulate the genetic material of microbial organisms, and because of their small genome sizes, sequencing the full genomes of evolved strains is trivial.
Therefore, comparisons can be made for the exact molecular changes in evolved strains during adaptation to novel conditions.
This article explains how such experiments are conducted, and contains annotated references for experimental evolution studies conducted with bacteriophages, as well as an expansion of a table presented by Breitbart et al.
(2005). 
A prohead or procapsid is an immature viral capsid structure formed in the early stages of self-assembly of some bacteriophages, including the "Caudovirales" or tailed bacteriophages.
Production and assembly of stable proheads is an essential precursor to bacteriophage genome packaging; this packaging activity can be replicated "in vitro".
The prohead structure may take a different shape from the head of a mature virion, as seen with the prohead of Bacillus subtilis phage φ29. 
The probes are prepared by cloning part of the gene of interest in a vector under the control of any of the following promoters, SP6, T7 or T3.
These promoters are recognized by DNA dependent RNA polymerases originally characterized from bacteriophages.
The probes produced are radioactive as they are prepared by in vitro transcription using radioactive UTPs.
Uncomplemented DNA or RNA is cleaved off by nucleases.
When the probe is a DNA molecule, S1 nuclease is used; when the probe is RNA, any single-strand-specific ribonuclease can be used.
Thus the surviving probe-mRNA complement is simply detected by autoradiography. 
SaPIs ("Staphylococcus aureus" or superantigen pathogenicity islands) are a family of mobile genetic elements resident in the genome of some strains of "Staphylococcus aureus".
Much like bacteriophages, SaPIs can be transferred to uninfected cells and integrate into the host chromosome.
Unlike the bacterial viruses, however, integrated SaPIs are mobilized by host infection with "helper" bacteriophages (specific SaPIs may require specific helper bacteriophages for mobilization, though Staphylococcus phage 80alpha appears to mobilize all known SaPIs).
One particular SaPI, SaPI1, is encapsidated in and exits the host cell in particles assembled from proteins encoded by its helper phage.