Tailed-viruses are lytic or temperate. Lytic infection results in production of progeny
viruses and destruction of the host. Phages adsorb tail-first to specific protein or
lipoprotein host cell receptors, which are located on the outer cell surface. In a few cases,
not represented by the genera described here, the primary adsorption sites are capsules,
flagella, or pili. Upon adsorption to the outside of the cell, virions undergo complex and
often poorly understood rearrangements which release the DNA to enter the cell through the tail. Cell walls are often locally digested by a virion-associated peptidoglycan hydrolase
and viral DNA enters the cytoplasm by as yet unknown mechanisms. In some cases DNA
entry is stepwise and transcription of the first DNA to enter is required for entry of the rest
of the DNA. Empty virions remain outside the infected bacterium, however most viruses
inject specific proteins with the DNA. Temperate viruses can, upon infection, either enter a
lytic growth cycle (above) or establish a lysogenic state (below). Physiological factors in the
cell can affect the decision between these two pathways.