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Should Bacteriophages Be Classified as Parasites or Predators?


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Fig. 1

Three developmental pathways of bacteriophages: lytic development (or lytic cycle) (panel A), lysogenization (or lysogenic cycle) (panel B), and permanent infection (or chronic cycle) (panel C). Phage virion (exemplified by a caudate phage in panels A and B, and a filamentous phage in panel C) adsorbs on the host cell and introduces its genome into this cell while the protein capsid remains outside the host. During the lytic development (A), the phage genome replicates intensively, and due to the expression of phage genes, structural proteins, forming capsids, are produced. After assembling progeny virions, the host cell is lysed due to the action of phage-encoded lytic proteins, and newly formed bacteriophages are liberated to the environment. During the lysogenic cycle (B), the phage genome integrates into the host chromosome by the site-specific recombination mechanism, forming a prophage, and it is passively replicated together with the bacterial nucleoid. In some cases, the phage genome can replicate as an extrachromosomal genetic element in the form of a plasmid. Under stress conditions, prophage is induced, phage DNA is excised from the host chromosome, and the development switches to the lytic mode. During the permanent infection (C), the development proceeds similarly to that during the lytic cycle; however, the host cell is not lysed when progeny phages leave the bacterium; thus, production of newly formed bacteriophages and their release into the environment proceed continuously.
Three developmental pathways of bacteriophages: lytic development (or lytic cycle) (panel A), lysogenization (or lysogenic cycle) (panel B), and permanent infection (or chronic cycle) (panel C). Phage virion (exemplified by a caudate phage in panels A and B, and a filamentous phage in panel C) adsorbs on the host cell and introduces its genome into this cell while the protein capsid remains outside the host. During the lytic development (A), the phage genome replicates intensively, and due to the expression of phage genes, structural proteins, forming capsids, are produced. After assembling progeny virions, the host cell is lysed due to the action of phage-encoded lytic proteins, and newly formed bacteriophages are liberated to the environment. During the lysogenic cycle (B), the phage genome integrates into the host chromosome by the site-specific recombination mechanism, forming a prophage, and it is passively replicated together with the bacterial nucleoid. In some cases, the phage genome can replicate as an extrachromosomal genetic element in the form of a plasmid. Under stress conditions, prophage is induced, phage DNA is excised from the host chromosome, and the development switches to the lytic mode. During the permanent infection (C), the development proceeds similarly to that during the lytic cycle; however, the host cell is not lysed when progeny phages leave the bacterium; thus, production of newly formed bacteriophages and their release into the environment proceed continuously.
eISSN:
2544-4646
Język:
Angielski
Częstotliwość wydawania:
4 razy w roku
Dziedziny czasopisma:
Life Sciences, Microbiology and Virology