Transmission electron micrograph of bacteria Escherichia coli, infected by T4 bacteriophages (black dots). Bacteriophages are viruses that infect only bacteria, T4 being specific to E.coli. They have no reproductive machinery & rely on the apparatus of bacteria in order to replicate. Several are seen here approaching the cell, to which they attach, injecting the DNA content of their heads into the cell. Within 30 minutesa new breed of phages (visible in the cells) are assembled. Bacteriophage' infection may lead to lysis, or death of the host cell by bursting. Mag: X40,000 (at 10x8 size).