1Sharing of genetic information

Bacteria are successful because

1. They carefully regulate their use of energy in metabolic processes by shutting down unneeded pathways at the biochemical and genetic levels.

2. They share genetic information with other bacteria, increasing their ability to adapt to their environment.

Genetic Recombination

• Bacteria are asexual– With sexual reproduction, multiplication and gene

recombination are linked.– In bacteria, they are separate– Bacteria acquire new DNA from mutation, phage

infection, and transfer from other bacteria• Bacterial genotypes are somewhat fluid

– Due to the ease of gene transfer, many genes can be widely distributed among many bacteria

– One multicomponent organism?

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3Gene transfer

• Ways that bacteria can acquire new genetic info– Transformation

• Taking up of “naked DNA” from solution– Transduction

• Transfer of DNA one to cell to another by a virus– Conjugation

• “Mating”: transfer of DNA from one bacterium to another by direct contact.

Transformation 4

http://openwetware.org/images/0/0c/Competence2.jpg

Both G+ and Gram – bacteria can take up DNA.

Cells in a state in which they can take up DNA are referred to as competent.

DNA may be actively released by some cells, suggesting that DNA exchange is “intentional”.

Transformation requires homologous recombination

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New DNA must be similar.

Successful transformation requires that donor and recipient be related.

Transduction: the vector is a virus

• New DNA brought by a bacteriophage– Requires donor and recipient be related

• Generalized transduction– Chopped up bacterial DNA is incorporated into a capsid– Phage binds to new host bacterium, but injects donor

bacterial DNA instead• Specialized transduction

– In lysogeny, virus DNA inserts.– If DNA excises, can take adjacent bacterial DNA with it– Upon infection of new host, new bacterial DNA added– Important in bacterial evolution

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7Gene transfer between bacteria-2• Transduction: transfer of

DNA via a virus.

Conjugation

• A plasmid that can be spread by conjugation codes for a sex pilus.

• Pilus attaches donor to recipient cell.– Shortening of pilus draws

bacteria into contact– Channel opens thru cell

wall of both bacteria• Copy of plasmid sent.

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http://parts.mit.edu/igem07/images/1/16/BU_conjugation.jpg

Conjugation and gene transfer

• Sex pili bind specifically to surface molecules on bacteria– But many bacteria have similar

molecules and can participate.• Homologous recombination is

not needed– Plasmids remain in cytoplasm– Once the plasmid has been copied and sent, both donor

and recipient bacteria have the genes. Recipient can now be a donor.

– Several types of plasmids, incl R, can be widely spread

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