Chapter 8 Microbial Genetics: Horizontal Gene Transfer (Down to

What is horizontal gene transfer? Is it only in bacteria? What is vertical gene transfer?

• Horizontal gene transfer is any transfer of DNA that results in organisms acquiring new genes that did not come from parent organisms

• An event in which one bacterium donates DNA to another bacterium (only in bacteria)

• Vertical gene transfer is when a parent, transfers their genes to their child

What is the end result of horizontal gene transfer? What is the new resulting strain called? What are some examples of the genes provided by this transfer?

• End result is a new strain different from both the donor and the original recipients

• Resulting new strain is called Recombinant: any organism that contains genes that originated in another organism

• Horizontal gene transfer provides genes for resistance to drugs and metabolic poisons, new nutritional and metabolic capabilities, and increased virulence and adaptation to the environment

Does horizontal gene transfer change genotype and phenotype of bacteria overtime? Does horizontal gene transfer involve chromosome DNA or plasmid DNA or both?

• Yes, it changes genotype and phenotype of bacteria that receives the genes overtime

• horizontal gene transfer can involve chromosome DNA or plasma DNA or both

What are plasmids? Are they independent of chromosome and can they replicate independently? Are they necessary for survival and what do they carry? Can they get rid of plasmid dna if not used?

• Small, circular pieces of extrachromosomal DNA

• Contain their own origin of replication

• Replicate independently

• Not necessary for survival: carry non-essential genes

• Can carry useful trait

• Can get rid of plasmid if not used

What are chromosome fragments and what are the three types of horizontal gene transfer?

Chromosomal fragments: Must integrate into the bacterial chromosome in order to be replicated

• The three types of horizontal gene transfer are conjugation, transformation, and transduction

For each type of horizontal gene transfer, describe what it is effective/limited at, if at all. Also does it requires direct or indirect touch with other cells?

1. Conjugation: effective for transferring many types of genes and requires direct physical contact

2. Transformation: Limited amount of genes and it can transfer through indirect contact

3. Transduction: can transfer through indirect contact

What are the factors involved for all three types of horizontal gene transfer?

1. Conjugation: Donor cell with pilus, Fertility plasmid in donor, Both donor and recipient alive, Bridge forms between cells to transfer DNA

2. Transformation: Free donor DNA (fragment) (naked DNA), Live competent recipient cell, dead donor cell

3. Transduction: Donor is lysed bacterial cell; Defective bacteriophage is carrier of donor DNA; Live recipient cell of same species as donor

What are the genes commonly transferred in nature of the three different types of horizontal gene transfer?

1. Conjugation: Drug resistance; resistance to metals; toxin production; enzymes; adherence molecules

2. Transformation: recombinant DNA, polysaccharide capsule

3. Transduction: toxin; enzymes for sugar fermentation; drug resistance

What is the four-point scheme we must remember for all three types of horizontal gene transfer?

1. Nature of donor cell

2. Nature of recipient cell

3. Nature of DNA being transferred (plasmid, chromosomal, etc.)

4. At the end of the process, what is the impact on donor and recipient cells?

What is naked DNA and what type of horizontal gene transfer is it in?

Naked DNA is DNA not enclosed in a cell and it is in the transformation type of horizontal gene transfer.

What is the four-point scheme for conjugation?

1. Nature of donor cell: alive cell with a F plasmid/pilus

2. Nature recipient cell: alive and lacks plasmid

3. Nature of DNA being transferred: All of plasmid or some plasmid & some chromosome

4. What’s the impact on donor and recipient:

• Donor: remains the same

• Recipient: gains resistances from plasmid and has the ability to form pili

What is the four-point scheme for transformation?

1. Nature of donor cell: dead lysed cell

2. Nature of recipient cell: competent alive cell with DNA-binding proteins capable of accepting DNA

3. Nature of DNA being transferred: NAKED DNA/small fragmented DNA in environment from lysed cell

4. What is the impact on donor and recipient cells:

• Donor cell lysed and DNA broken down into small fragments

• Recipient cell accepts some fragments of DNA and can replicate it

What is the four-point scheme for transduction?

1. Nature of donor cell: Bacteriophage

2. Nature of recipient cell: regular bacterial cell

3. Nature of DNA being transferred: the original lysed bacterial cell DNA fragments

4. What is the impact on donor and recipient cells:

• Donor cell: destroyed/hijacked and DNA is taken into another bacterial cell

• Recipient cell: receives original bacterial DNA fragments and accepts genes

Describe what conjugation is between two cells and what is essential for it. What type of DNA can be transferred? What is a fertility (F factor) or F plasmid?

• Plasmid (plasmid is essential) mediated genetic exchange between two bacterial cells

• A plasmid DNA alone or plasmid plus chromosomal DNA is transferred by a donor to a recipient cell via a direct connection

• Fertility (F factor) or F plasmid allows synthesis of conjugative pili which form the bridge between donor and recipient cells through which DNA is transferred

What are the two types of conjugation?

1) F+ donor cell: plasmid transfer (entire plasmid)

2) Hfr donor cell: some plasmid plus some chromosome transfer

Describe the five steps of F+ conjugation. Does the donor still keep a copy of the plasma being transferred?

• F+ donor cell has the plasmid, produces pili that bring the cells together

• F- recipient cell lacks the plasmid

• Conjugation is a conservative process in which the donor bacterium retains (“conserves”) a copy of the plasmid being transferred

• F+ Donor transfers a copy of F plasmid to F- recipient cell.

• F- recipient cell now becomes F+ capable of producing pili and conjugating with other cells

What are Hfr donors in conjugation? What is transferred to the other cell?

• High-frequency recombination (Hfr) donors: Plasmid becomes integrated into the donor’s chromosome

• plasmid begins to transfer to the recipient cell

• Some chromosomal genes get transferred to the recipient, but entire chromosomal DNA does not get transferred

After Hfr type of conjugation, what is the new recipient cell called? Can this new cell be a donor? explain why it is not the other names

• It is called a F- recombinant cell

• It cannot be a donor cell because it must have the whole plasma to be a donor cell

• Not F+ Because it does not have the whole F Plasmid; Not Hfr because it doesn’t have a whole plasma integrated in the chromosome; Not F- because it doesn’t fully lack of plasmid

in transformation what is the donor cell and what is the recipient cell? What are the two other names for both cells? what is the impact on the DNA from the donor cell to both cells?

• A Donor cell is a dead cell: chromosome released by a lysed donor cell breaks into fragments small enough to be accepted by a recipient cell (Cells don’t always accept the DNA)

• A Recipient cell is a Competent cell: cells that are capable of accepting genetic material, has DNA-binding proteins on the cell wall (that accepts the DNA)

By the definition of transformation. Does it require special appendages? Is the impact on recipient cells variable?

Transformation: Nonspecific acceptance by a bacterial cell of small fragments DNA (naked DNA) from the environment

• Requires no special appendages

• Impact on recipient cell is a variable due to the naked DNA that’s accepted

What is transformation useful for and what is this technology?

Useful for certain types of recombinant DNA technology:

• Foreign genes from a completely unrelated organism are inserted into a plasmid

• Plasmid is introduced into a competent bacterial cell through transformation

• Can be carried out in a test tube

What is transduction dependent on? What are bacteriophages And what do most of them contain in their captured? Are bacteria infected by bacteriophages pathogenic?

Bacteriophage: “bacteria eating”:

• Most bacteriophages contain double-stranded DNA in their capsid

• They infect bacteria

• The bacteria infected by bacteriophages are often more pathogenic for huma

List and describe the General phases of the bacteriophages replication cycle

1. Adsorption: the bacteriophage attaches

2. Penetration: it injects its DNA into cell

3. Synthesis: in the cytoplasm of the infected cell phases synthesize phage parts for replication (proteins, lipids, etc.) and destroys bacterial DNA so it can take over

4. Assembly: new phases Are made using the stuff from synthesis phase and sometimes forms defective phages

5. Release and lysis of the bacterial cell

During the assembly phase of bacteriophage replication What can happen? What causes it?

In the assembly phase sometimes phages are defective meaning it is packaged with bacterial DNA and not phage DNA

• Caused by mispackaging of the capsid

What is the case of piggyback DNA in transduction?

• The defective Bacteriophage (lytic phage) serves as a carrier for the original bacterial cell DNA from a donor cell to a recipient cell

• Random fragments of disintegrating host (original destroyed bacterial cell) DNA are taken up by the bacteriophage

• Virtually any gene from the bacterium can be transmitted