bacteriophage lambda

:  a bacteriophage (species Enterobacteria phage λ of the family Siphoviridae) that consists of a flexible tail and an icosahedral head containing double-stranded DNA and that can be integrated as a prophage into the genome of some strains of E. coli ◆Bacteriophage lambda is used as a vector to clone DNA from various organisms by replacing nonessential DNA in the bacteriophage with foreign DNA and introducing the combined DNA into E. coli, where it is replicated with the bacterium. —called also lambda phage, phage lambda