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A T4 bacteriophage arrives in a colony of E. coli. After the virus recognizes and binds to a host cell using receptor binding domains on its tail fibers that recognize bacterial surface epitopes, its tail sheath contracts, injecting its dsDNA (orange) into the cell cytoplasm. ⠀⠀⠀⠀⠀⠀⠀⠀⠀ The DNA is transcribed to RNA, which then shuts down normal processes in the cell and instead directs the synthesis of viral proteins inside the bacterium. Some of these proteins self-assemble to package new DNA and form as many as several hundred new bacteriophages. At this point the RNA directs the synthesis of endolysins which rupture the host cell membrane from the inside, liberating new bacteriophages to start the cycle again if they encounter another host cell. ⠀⠀⠀⠀⠀⠀⠀⠀⠀ Bacteriophages were used extensively in the Soviet Union to treat bacterial infections while western medicine
