• Bacteria have a single circular chromosome

• Double-stranded DNA

• Haploid for all genes

• Can have extra-chromosomal DNA

• Plasmids

• Bacteria reproduce via binary fission

• Cannot undergo meiosis

• No synapsis, no crossing over

• When cell divides, the chromosome and any plasmid(s) will be duplicated and divided evenly

• Can still undergo genetic recombination

• Horizontal Gene Transfer

• Transfer of genetic material from one bacterium to another of a different species

• Confers new genes/traits on bacteria that never had them before

• E.g., nutrient production, antibiotic resistance

• Conjugation

• Transformation

• Transduction

• Vertical Gene Transfer

• Transfer of genetic material from one bacterium to another of the same species

• AKA – reproduction!

• A) They have only one chromosome

• B) They have two circular chromosomes

• C) They must undergo meiosis prior to fertilization

• D) All of the above

• A) Involves synapsis

• B) Occurs during Prophase I

• C) Involves replacing similar genes with new ones

• D) Occurs during reproduction

Lederberg

and

Tatum,

1946

Davis

Physical contact occurs

via sex pilus

The gene product of the

F (fertility) factor confers

ability to donate part of the

chromosome during

conjugation

In most conjugations, this

transfer (recombination)

rarely occurs, even though

F factor is always transferred

• A new species of bacteria gains the F factor

• The new species of bacteria, now F+, has not gained any other traits

• So…who cares?

• Some bacterial strains were discovered to have a much higher rate of recombination than typically observed

• 1/104, rather than 1/107

• Hfr bacteria were found to have the F factor incorporated into chromosome, instead of as a plasmid

• Transfers in Hfr include chromosomal DNA, rather than plasmid DNA

• Hfr transfers studied using the interrupted mating technique

• Mix two cultures, wait a specified period of time, then shear cells apart using a blender

• Repeat with different periods of time, but the same bacterial crosses

• Transfer always begins just after the F factor insertion point Origin (O)

• Insertion of F factor is random, so for any newly-generated Hfr strain, the starting point of genes will be different

• The overall order of gene transfer will always be the same for newly-generated Hfr from the same parent strain

• Order of transfer is used to map bacterial chromosomes

• Use multiple Hfr strains to map one parent strain, since complete chromosome is never transferred

• Who cares if F factors are transferred?

• It matters if that F factor subsequently inserts into the bacterial chromosome, converting an F+ into an Hfr

• That Hfr cell can now transfer genes to F- cells at a high rate

• Antibiotic resistance

• Nutrient production

• Theoretically any bacterial gene for which a similar gene is already present

• Sometimes in Hfr, the F factor becomes excised from the chromosome

• At the same time, genes from chromosome can be carried with it

• This creates a new plasmid containing F factor AND (formerly) chromosomal genes

• This F’ cell can initiate conjugation, and transfer F factor AND genes easily

• So…

• F- F+ Hfr F’ easy transfer of genes

• A) F-

• B) F+

• C) F’

• D) B and C

• E) All of the above

• A) F-

• B) F+

• C) F’

• D) B and C

• E) All of the above

• Many bacteria are able to pick up naked DNA out of the aqueous environment

• Must be competent

• Active transport process requires energy and specific transporters

• Integration of new DNA into host chromosomes forms heteroduplex DNA

• Recombination involves replacing ONE strand of DNA, not both

• Bacteria can receive new genetic information via viral infection

• A) conjugation

• B) transformation

• C) transduction

• D) all of the above