Biosynthesis is the stage of bacteriophage infection where the virus degrades the host chromosome using virus-encoded endonucleases. The virus then hijacks the host cell's machinery to replicate, transcribe, and translate key viral components (such as capsomeres, sheaths, base plates, tail fibers, and viral enzymes) for assembling new viruses, with polymerase genes expressed early and capsid and tail proteins expressed later in the cycle.

Biosynthesis of Bacteriophage

The replication steps for bacteriophages generally include attachment to the host, entry or penetration of the viral genome, replication and synthesis of viral components (biosynthesis), assembly of new phages (maturation), and release of progeny virions (lysis).

Steps of Bacteriophage Replication

During attachment, the first stage of the lytic cycle, a bacteriophage interacts with specific surface receptors on the host bacterium (such as lipopolysaccharides and OmpC proteins). Phages typically exhibit a narrow host range, restricting infection to particular bacterial species or specific strains.

Attachment of Bacteriophage

Penetration is the second stage of the lytic cycle, where the bacteriophage contracts its tail sheath like a hypodermic needle to inject its viral genome through the host cell wall and membrane, while the phage head and other components remain outside the cell.

Penetration of Bacteriophage (Lytic Mechanism)

Maturation is the stage of the bacteriophage lytic cycle in which newly synthesized viral components are assembled to form complete, new phage particles within the host cell.

Maturation of Bacteriophage

Lysis is the final stage of the bacteriophage replication cycle, where the bacterial cell wall is disrupted by phage proteins such as holin or lysozyme. This disruption causes the host cell to burst, releasing the newly assembled progeny viruses into the environment to infect new cells.

Lysis of Bacteriophage

Generalized transduction is a process of horizontal gene transfer in which a bacteriophage incorrectly packages a random fragment of the host bacterium's degraded chromosome into its capsid instead of viral DNA during the lytic cycle. When this phage infects a new bacterial cell, it injects the previous host's DNA. This asexual gene transfer can lead to DNA recombination, providing the recipient bacterium with new genes, such as those for antibiotic resistance or sugar metabolism.

Generalized Transduction

During the lytic cycle, a virulent bacteriophage takes over the host bacterial cell, replicates its viral genome, synthesizes proteins to assemble new phages, and ultimately destroys the host cell by cell lysis to release progeny viruses.

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Bacteriophage replication can proceed through two main pathways: the lytic cycle, which involves replicating viral parts, assembling them into virions, and lysing the host cell to release them; and the lysogenic cycle, where the viral DNA integrates into the host chromosome as a prophage and replicates alongside it, potentially excising itself to enter the lytic cycle under stress.

Bacteriophage Replication Cycles

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This type of bacteriophage does not kill the host cell right away, rather the phage genome integrates into the bacterial chromosome and becomes apart of the host. Then, as the host divides into daughter cells the phage genome is also replicated. Eventually, the host cell becomes stressed, the phage genome exits the host, makes more phage particles, and then the virus exits the host DNA resulting from lysis.

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