1. 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? 1

2. 2 Gene 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.

3. Transformation 3 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”.

4. Transformation requires homologous recombination 4 New DNA must be similar. Successful transformation requires that donor and recipient be related.

5. 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 5

6. 6 Gene transfer between bacteria-2 Transduction: transfer of DNA via a virus.

7. 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. 7 http://parts.mit.edu/igem07/images/1/16/BU_conjugation.jpg

8. 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 8

9. 9 Regulation of genetic information Bacteria are successful because 1.They share genetic information with other bacteria, increasing their ability to adapt to their environment. 2.They carefully regulate their use of energy in metabolic processes by shutting down unneeded pathways at the biochemical and genetic levels.

10. 10 Bacteria tightly regulate their activities Bacteria must respond quickly to changes in the environment. Bacteria are small compared to their environment, have no real capacity for energy storage. Simultaneous transcription and translation allows them to synthesize the proteins they need quickly. Wasteful activities are avoided. If there are sufficient amounts of some metabolite, bacteria will avoid making more AND avoid making the enzymes that make the metabolite. Biosynthesis costs! Biochemical regulation and genetic regulation.

11. 11 Biochemical regulation: allosteric enzymes Allo = other; steric = space. Many enzymes not only have an active site, but an allosteric site. Binding of a molecule there causes a shape change in the enzyme. This affects its function.

12. 12 Feedback inhibition of pathways

13. 13 Genetic regulation Genotype is not phenotype: bacteria possess many genes that they are not using at any particular time. Transcription and translation are expensive; why spend ATP to make an enzyme you don’t need? Examples: –Induction of lactose operon –diauxic growth with sugars.

14. 14 More on Regulation In biochemical regulation, processes like feedback inhibition prevent wasteful synthesis. To save more energy, bacteria prevent the synthesis of unneeded enzymes by preventing transcription. –In operons, several genes that are physically adjacent are regulated together. Two important patterns of regulation: Induction and repression. –In induction, the genes are off until they are needed. –In repression, the genes normally in use are shut off when no longer needed.

15. 15 Operons and Regulons Nearly 50 years ago, Jacob and Monod proposed the operon model. Many genes in prokaryotes are grouped together in the DNA and are regulated as a unit. Genes are usually for enzymes that function together in the same pathway. At the upstream end are sections of DNA that do not code, but rather are binding sites for proteins involved in regulation (turning genes on and off). The Promoter is the site on DNA recognized by RNA polymerase as place to begin transcription. Operator is location where regulatory proteins bind. Promoter and Operator are defined by function.

16. 16 Binding of small molecules to proteins causes them to change shape Characteristic of many DNA-binding proteins Regulation of operons: Inducible operons: Repressor protein comes off DNA Repressible operons: Repressor protein attaches to DNA

17. Binding of lac repressor to DNA 17 More lac Repressor Research - Lewis & Lu Labs

18. Lac repressor 18 Each different colored ribbon structure is a polypeptide; the repressor is a tetramer and binds both to allolactose the inducer and the DNA.