Microbiology Chapter 9: Exchange of DNA between Bacteria

DNA recombination

-A type of genetic transfer in which DNA from one organism is donated to another. -Combining DNA from two different organisms • Bacterial recombination - often an exchange of plasmids - can exchange chromosomal fragments • Recombinant = the microbe that contains and expresses genes that originated in another microbe

3. Describe the process of bacterial transformation. a. What type of DNA is transferred and where does it come from?

Uptake of DNA from the environment - DNA released from dead cells and degraded into small pieces • DNA binds proteins on recipient cell and is transported across the membrane • Chromosomal integration

4. Generalized transduction: a. What type of DNA is transferred? b. How is the DNA transferred how?

• Transfer of bacterial DNA from one cell to another by a bacteriophage A. Bacterial B. bacteriophage - Pieces of host DNA are picked up by a bacteriophage during assembly and delivered to the next host cell

chromosomal DNA

dna

Horizontal gene transfer

= when a organism acquires genes from a source other than it's parent organism - CONJUGATION - TRANSFORMATION - TRANSDUCTION

4. plasmid DNA

A plasmid is a small, circular, double-stranded DNA molecule that is distinct from a cell's chromosomal DNA. Plasmids naturally exist in bacterial cells, and they also occur in some eukaryotes

Describe the main features of conjugation in Gram-negative bacteria.

Bacteria that can conjugate = F+ F plasmid carries genes to form the sex (F) pilus = DONOR • F-bacteria = recipients -Sex pilus binds to a recognition site on the surface of F- cell • Onceconnected,thepilus retracts, and DNA is transferred

conjugation pilus (also called F pilus or sex pilus)

Donor plasmid that allows synthesis of a pilus in bacterial conjugation. Presence of the factor is indicated by F+, and lack of the factor is indicated by F-. -Long, tubular structures made of pilin protein produced by gram-negative bacteria and used for conjugation.

c. What is different about Hfr conjugation?

Occurs when bacteria have F factor integrated into the chromosome • Entirechromosomeis copied and transfer begins -Often, sex pilus breaks before the entire chromosome is transferred -Fragment containing F factors is transferred

2. How does conjugation between Gram positive bacteria differ from Gram negative?

Recipient bacteria secrete pheromones • Pheromonesbindtoreceptorson donor bacteria - Binding triggers expression of transfer (tra) genes • Cells join,cell walls and membranes fuse to form a mating bridge • Plasmids transferred from donor to recipient

Conjugation

Requirescontactbetween bacteria • Plasmidsareusuallytransferred • Twoformsofconjugation - Gram negative conjugate via a sex pilus - Gram positive conjugate via a mating bridge • Usually occurs between two closely related species

a. What types of cells are able to form a conjugation pilus?

gram -

b. What type of DNA is usually transferred during conjugation?

plasmids and sometimes chromosomal