Genetics of Bacteria

Bacterial Chromosomes

• One double-stranded, circular molecule of DNA.• Found in nucleoid region, which is a dense

region of DNA.• Many bacterial also contain extrachromosomal

DNA, in the form of a plasmid, which is a small double-stranded ring of DNA.

• DNA is replicated bidirectionally from a single origin of replication, and is then followed by Binary Fission.

Binary Fission

• Asexual reproduction via Mitosis that is used by most bacteria to rapidly reproduce.

• It produces a clone, which is genetically identical to the parent.

Genetic Recombination in Bacteria

• Produces new bacterial strains with different genetics.

• 3 Types:o Transformationo Transductiono Conjugation

Transformation

• Change of a bacterial cell’s genotype by the uptake of foreign DNA plasmid from its surrounding environment when the bacteria is stressed.

• Process can be induce in a lab very easily.

• Used in biotech industry to produce copies of genes and so bacterial cells can produce proteins of other species.

• Ex: Insulin, Human Growth Hormone

Transduction

• Transfer of DNA from one bacteria to another by a bacteriophage.

• 2 Types: Generalized and Specialized.QuickTime™ and a

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Generalized Transduction

• Occurs when random pieces of host cell DNA are packaged within a phage capsid during the Virus Lytic Cycle.

• Phage within host cell (donor cell) DNA infects a new host (recipient cell).

• Donor cell’s DNA recombines with the recipient cell’s DNA.

• Results in a recombinant bacterial cell with a genotype different from the donor and recipient cells.

Specilized Transduction

• Occurs when a prophage (virus) excises from the bacterial chromosome & carries adjacent bacterial genes with it.

• Carried out only by temperate phages.

Conjugation• Direct transfer of genes between 2 cells that are

temporarily joined.• Physical connection (pili).• Bacterial version of sex.• F-factor:

– F = fertility.– Codes for sex pili = male.– If F-factor is carried in a plasmid = F plasmid.

• HFr:– F-factor integrates into chromosome.

Conjugation (Continued)• Conjugation bridge usually breaks before entire

chromosome and tail end of F-factor can be transferred. • As a result:

– Only some bacterial genes are donated.– F- cell does not become F+ cell because only part of

the F-factor is transferred.

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