All About Bacteriophages
                     ALL ABOUT 
BACTERIOPHAGES
Introduction
Bacteriophages, also known as phages, are viruses that infect and 
replicate only in bacterial cells. They are ubiquitous in the 
environment and are recognized as the most abundant biological 
agent on earth. They are extremely diverse in size, morphology, and 
genomic organization
Source: www.ncbi.nlm.nih.gov
Electron microscopy 
Electron microscopy has allowed the detailed visualization of 
hundreds of phage types, some of which appear to have "heads," 
"legs", and "tails". Despite this appearance, phages are non-
motile and depend upon Brownian motion to reach their targets.
Source: www.ncbi.nlm.nih.gov
Species
Like all viruses, bacteriophages are very species-specific with regard 
to their hosts and usually only infect a single bacterial species or 
even specific strains within a species. Once a bacteriophage 
attaches to a susceptible host, it pursues one of two replication 
strategies: lytic or lysogenic. 
Source: www.ncbi.nlm.nih.gov
Replication cycle
During a lytic replication cycle, a phage attaches to a susceptible host 
bacterium, introduces its genome into the host cell cytoplasm, and 
utilizes the ribosomes of the host to manufacture its proteins. The host 
cell resources are rapidly converted to viral genomes and capsid 
proteins, which assemble into multiple copies of the original phage. 
Source: www.ncbi.nlm.nih.gov
Lysogenic replication cycle
As the host cell dies, it is either actively or passively lysed, 
releasing the new bacteriophage to infect another host cell. In the 
lysogenic replication cycle, the phage also attaches to a 
susceptible host bacterium and introduces its genome into the host 
cell cytoplasm. 
Source: www.ncbi.nlm.nih.gov
Function
Although bacteriophages cannot infect and replicate in 
human cells, they are an important part of the human 
microbiome and a critical mediator of genetic exchange 
between pathogenic and non-pathogenic bacteria.
Source: www.ncbi.nlm.nih.gov
DNA as the host cell 
In "generalized" transduction, random pieces of 
bacterial genomic DNA are packaged inside phage 
capsids in place of phage genomic DNA as the host 
cell is disintegrating from lytic replication. 
Source: www.ncbi.nlm.nih.gov
Specialized transduction
In "specialized" transduction, it is thought that 
lysogenic phages, which have been amplified in a 
population of bacteria, excise some bacterial DNA with 
their genome when initiating a lytic replication cycle. 
Source: www.ncbi.nlm.nih.gov
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