The lambda variety engages in the lysogenic cycle, but most infect a cell via attachment, penetration, multiplication, and eventual bursting of the host cell in the lytic cycle.  
Seymour Benzer extensively studied the genetics of these entities, whose P1, Mu, and M13 varieties are often used as cloning vectors.  Radioactive P-labeled DNA was inserted into the genomes of these entities, proving that DNA was the genetic material, in the Hershey Chase experiment.  The lambda variety engages in the lysogenic cycle, but most infect a cell via attachment, penetration, multiplication, and eventual bursting of the host cell in the lytic cycle.  For 10 points, name these viruses that attack a certain type of single-celled organism.
Seymour Benzer extensively studied the genetics of these entities, whose P1, Mu, and M13 varieties are often used as cloning vectors.  
{bacteriophages} [prompt on “{virus}” or “{phage}”]