Microbial genetics has revealed that genes consist of DNA, an observation that laid the foundation for molecular biology.
Subsequent investigations of bacteria revealed the presence of restriction enzymes that cleave DNA at specific sites, giving rise to DNA restriction fragments.
Amplification of specific regions of DNA also can be achieved with bacterial enzymes using the polymerase chain reaction (PCR) or other enzyme-based methods of nucleic acid amplification (e.g. transcription-mediated amplification).
The involvement of relatively short transposons (750–2000 bp long), known as insertion elements, produces the majority of insertion mutations
These insertion elements (also known as insertion sequence [IS] elements) carry only the genes for enzymes needed to promote their own transposition. Almost all bacteria carry IS elements, with each species harboring its own characteristic ones.
Unusual bases such as hydroxymethylcytosine are sometimes found in the phage nucleic acid.
Many phages contain specialized syringe-like structures that bind to receptors on the cell surface and inject the phage nucleic acid into a host cell
Bacteriophages infect bacterial cells and either replicate to large numbers and cause the cell to lyse (lytic infection) , or in some cases integrate into the host genome without killing the host (the lysogenic state ), such as the E. coli bacteriophage lambda.
Some lysogenic bacteriophages carry toxin genes (e.g., corynephage beta carries the gene for the diphtheria toxin).
Bacteriophage lambda remains lysogenic as long as a repressor protein is synthesized and prevents the phage from becoming unintegrated and replicating independently of the host chromosome.
This reaction can be triggered if the host cell DNA is damaged by radiation or by another means or if the cell can no longer make the repressor protein, a signal that the host cell is unhealthy and is no longer a good place for "freeloading."
www.themegallery.com Lysogenic infection of bacterium with temperate bacteriophage. A, The phage infects a sensitive bacterium, and the phage DNA is injected. B, The phage DNA becomes integrated into the bacterial chromosome. C, The bacterium multiplies, apparently unaffected by the infection. It has been lysogenized. D, Occasionally the phage DNA is excised from the bacterial chromosome, takes control of the cell, and replicates. E, An individual cell (or, by induction, all the cells) produces phage components. F, The components are later assembled into phage particles. G, Ultimately, the cell lyses and releases mature phage particles
transformation, which results in acquisition of new genetic markers by the incorporation of exogenous or foreign DNA;
transduction, which is the transfer of genetic information from one bacterium to another by a bacteriophage. Once inside a cell, a transposon can jump between different DNA molecules (e.g., plasmid to plasmid or plasmid to chromosome
Conjugation results in one-way transfer of DNA from a donor (or male) cell to a recipient (or female) cell through the sex pilus.
Conjugative R (antibiotic resistance) for gram-positive bacteria, such as streptococci, streptomyces, and clostridia, are brought together by the presence of an adhesin molecule on the surface of the donor cell instead of pili.
Genetic transfer by transduction is mediated by bacterial viruses (bacteriophages), which pick up fragments of DNA and package them into bacteriophage particles.
The DNA is delivered to infected cells and becomes incorporated into the bacterial genomes.
Transduction can be classified as specialized if the phages in question transfer particular genes (usually those adjacent to their integration sites in the genome) or generalized if the selection of the sequences is random because of accidental packaging of host DNA into the phage capsid