Chapter 11: Genetic Exchange in Bacteria

All three methods are likely important in nature, but ___________ is likely the most important in medicine

conjugation -Clinical emergence of resistance often involves conjugation. Cell-to-cell contact is likely to occur at high rates in the gastrointestinal tract of humans under antibiotic treatment (grow in biofilm)

•Define "competence". a.The ability of a cell to replicate its genome b.The ability of a cell to transfer DNA to another cell through an F-pilus c.The ability of a cell to outcompete another cell through natural selection d.The ability of a cell to take up extracellular DNA from the environment

d.The ability of a cell to take up extracellular DNA from the environment

Horizontal gene transfer

information passed to one cell to another without replication can even happen between members of different species -E. coli is not normally pathogenic -It can become a pathogen if it receives a plasmid from Shigella (shigella can cause dysentery) -example: ground beef has E.coli that can be pathogenic

F plasmid

the F factor in its plasmid form

transposable element

A segment of DNA that can move within the genome of a cell by means of a DNA or RNA intermediate; also called a transposable genetic element.

Pilus

A short, thick hair-like protein structure that allows a bacterium to attach to other bacteria and surfaces or share genetic information in conjugation

plasmid

A small ring of DNA that carries accessory genes separate from those of the bacterial chromosome

Bacteria acquire external genetic material through three main strategies

All three methods are likely important in nature, but conjugation is likely the most important in medicine TRANSFORMATION: Griffith's experiment TRANSDUCTION: bacteriophage CONJUGATION: sex pilus

MRSA

Conjugation involving a plasmid carrying the gene for resistance to methicillin is suspected to have resulted in MRSA

6-Anilinouracils are selective inhibitors of bacterial DNA polymerase III. How would this drug affect the bacterial cell? A. It would not be able to unwind supercoiled DNA B. It would not be able to create a copy of DNA from a DNA template C. It would not be able to create RNA from DNA D. It would not be able to synthesize protein

B. It would not be able to create a copy of DNA from a DNA template

What is the function of RNA primase? A. to add a RNA primer to double stranded DNA B. to add an RNA primer to single stranded DNA C. to add an RNA primer to double stranded RNA D. to add an RNA primer to single stranded RNA

B. to add an RNA primer to single stranded DNA

bacterial transfer of genetic information

Bacteria can transfer genetic information to offspring and other, non-offspring cells. For example, it is estimated that 20% of E. coli's genome was acquired through horizontal gene transfer

again, why do bacteria get ride of some genetic info?

Because expressing and replicating antibiotic resistance genes costs energy and resources, bacteria will quickly drop resistance genes if no antibiotics are present

A plasmid was discovered in K. pneumoniae that contained genes for lactose fermentation and resistance to ampicillin. It can readily transfer to Salmonella. Under which conditions would this plasmid disappear from the population A. in the presence of lactose and ampicillin B. in the presence of lactose and absence of ampicillin C. in the absence of lactose and presence of ampicillin D. In the absence of both lactose and ampicillin E. This plasid would not disappear because it is required for Salmonella's survival

D. In the absence of both lactose and ampicillin

horizontal vs vertical gene transfer

HORIZONTAL •Can happen between members of different species. •Transfer to non-offspring. VERTICAL •Passed down from generations. •Example: Parent to offspring

If bacteria are capable of acquiring genes through these three mechanisms, why don't all bacteria have all possible genes? In other words, why do bacteria keep genes and discard others?

Keeping genes is energetically and resource expensive to continue making copies of genes bacteria quickly get rid of genetic information that does not confer a selective advantage Can usually wait out antibiotic resistance if its not in chromosome (selective inversion). Susceptible population outgrows resistant bacteria bc it is using less energy in gene replication. Then we treat with antibiotic. resistance does not last that long unless you are in a clinical setting

Griffith's experiment

Reported in 1928 by Fredrick Griffith, was the first experiment suggesting that bacteria are capable of transferring genetic information through a process known as transformation Uses Streptococcus pneumonia -smooth strain has capsule mouse dies -rough strain does not have capsule so mouse lives -heat killed smooth mouse lived -heat killed smooth and alive rough= killed mouse and could be isolated as alive smooth

•True/False: Virulent phages kill the host cell.

TRUE

•Which process requires cell-to-cell contact for DNA transfer? a.Conjugation b.Transformation c.Transduction d.Conjugation and Transformation

a.Conjugation

•In Griffith's experiment, rough, non-virulent strains of S. pnuemominae became smooth, virulent strains when mixed with heat killed smooth strain cells. This experiment demonstrates... a.Transformation b.Conjugation c.Transduction d.Transposition e.Vertical gene transfer

a.Transformation

•Gene transfer in bacteria is: a.Unidirectional- From donor cells to recipient cells b.Unidirectional- From recipient cells to donor cells c.Bidirectional d.Multidirectional

a.Unidirectional- From donor cells to recipient cells

•A virus that infects a bacterial cell is known as a: a.Bacteriolysin b.Bacteriophage c.Bacteria virus d.Baculovirus

b.Bacteriophage

transposition

bacteria can transpose genes into plasmids (or vice versa) antibiotic resistance: plasmid to chromosome

vertical gene transfer

binary fission resulting in two identical daughter cells with slight possible variation due to mistakes

•Which process relies on phage as a vehicle of DNA transport? a.Conjugation b.Transformation c.Transduction d.Conjugation and Transformation e.Transformation and Transduction

c.Transduction

Tetracycline resistance

involves the production of specialized proteins tetracycline inhibits translation by binding to the A site of the ribosome, physically blocking tRNA from binding to the mRNA TetO is a protein produced by the cell binds to the A site, causing tetracycline to release Because expressing and replicating antibiotic resistance genes costs energy and resources, bacteria will quickly drop resistance genes if no antibiotics are present If tetracycline is present, resistance will spread throughout a population/community If tetracycline is absence, resistance genes will decrease in abundance

Transformation

involves the uptake of short fragments of naked DNA by naturally transformable bacteria Griffith's experiment is the uptake of naked DNA from the environment (incorporation of naked DNA) -Only a handful of clinically relevant bacterial species are able to "naturally" incorporate naked DNA to develop resistance

Transduction

involves transfer of DNA from one bacterium into another via bacteriophages genetic exchange facilitated by viruses errors in replication and/or packaging of the viral genome can pass on to the next host lysogenic cycle: accidently pick it up (phage mediated) -it's not clear how important transduction is in clinical antibiotic resistance, but transduction may be an important HGT mechanism in aquatic environments

Conjugation

involves transfer of DNA material via sexual pilus and requires cell-to-cell contact is effectively bacterial sex a bacterium (donor) with an F plasmid and pilus approaches a bacterium (recipient) without an F plasmid The pilus attaches to the recipient The F plasmid replicates and transfers to the recipient Both bacteria now have the plasmid (bacterial "sex") -Clinical emergence of resistance often involves conjugation. Cell-to-cell contact is likely to occur at high rates in the gastrointestinal tract of humans under antibiotic treatment (biofilm)

competence/competency

is the ability of a bacterium to transform (take up naked DNA) -usually destroy it -integrate it to genome -exist as a plasmid No bacteria are competent all the time; special conditions must be met in order for a bacterium to transform

PREVIOUS: A plasmid was discovered in K. pneumoniae that contained genes for lactose fermentation and resistance to ampicillin. It can readily transfer to Salmonella. This plasmid disappear from the population in the absence of both lactose and ampicillin TRUE/FALSE: In the previous question, the plasmid would not disappear immediately. It would persist for several generations in the absence of lactose and ampicillin

true

What are the 3 main strategies that bacteria can acquire genetic material and how do they function?

•1. Transformation: Involves uptake of short fragments of naked DNA by naturally transformable bacteria. •2. Transduction: Involves transfer of DNA from one bacterium into another via bacteriophages. •3. Conjugation: Involves transfer of DNA material via sexual pilus and requires cell-to-cell contact.

What does competency mean in terms of genetic exchange?

•Ability of a bacterium to transform •No bacteria are competent all the time •Special conditions must be met

Explain why bacteria keep some genes and discard others Tetracycline Example

•Tetracycline= Inhibits translation by binding to the A site of the ribosome and blocks tRNA from binding to the mRNA. •Tetracycline is released when TetO binds to the A site. •Expressing antibiotic resistance genes costs energy so bacteria will drop resistance genes if no antibiotics are present. •If tetracycline is present= resistance will spread •If tetracycline is absent= resistance genes will decrease. •Bacteria do this in order to be more efficient.