Fig. 1

An overview on structure, morphology, and life cycles of bacteriophages. A A schematic of typical bacteriophage structure (T4). B A diagram illustrating life cycles of bacteriophages which starts with the attachment of phage particle to the cell surface and followed by phage genome insertion. Phages can apply four life cycles during infection: (1) in lytic cycle, phage genome is replicated, new virions are synthesized and released through the bacterial cell lysis; (2) in lysogenic cycle, phage genome is integrated into the bacterial genome or in a plasmid-like construct (episomal state) as a prophage, and replicated with the bacterial chromosome as long as bacteria divide. The prophage remains in a dormant state in the infected bacteria unless encountering a stimulating factor, such as antibiotics, ultraviolet radiation, temperature or pH alterations, which may cause resuming a lytic cycle; (3) in bacterial budding cycle, phages can bud out of bacterial cells and protect the host cell from lysis or death; (4) in pseudolysogenic cycle, the phage genome remains as an episomal in the host cell without integration into the host genome or replication. C Representation of bacteriophage morphotypes including tailed, polyhedral, filamentous, and pleomorphic phages, following with some examples for each morphotype