Chapter 6: Genetic Analysis in Bacteria and Bacteriophages

horizontal gene transfer

The transfer of genes from one genome to another through mechanisms such as transposable elements, plasmid exchange, viral activity, and perhaps fusions of different organisms. transfer of info between related but distinct species. - bacterial analysis

Lysogeny

Phage DNA integrates into bacterial chromosome and coexists -Prophage Replicated along with the chromosome Passed to daughter cells No lysis of host cell

lytic cycle vs lysogenic - both

Phage injects its DNA into the host cell. Phage attaches to host cell. Phage chromosome circularizes.

complete medium

contains all the substances, such as the amino acid leucine, required by bacteria for growth and reproduction. *auxotrophs* Amino acids are added as supplements to minimal medium

Transduction

conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brains can interpret. Bacterial recombination mediated by bacteriophages---> *injection of foreign dna by a phage into host bacterium cell* Lederberg-Zinder experiment Used Salmonella (auxotrophic strains) Led to discovery of phage transduction in bacteria

Holiday Junction

cross-shaped structure that forms during the process of genetic recombination, when two double-stranded DNA molecules become separated into four strands in order to exchange segments of genetic information.

adaptation hypothesis

interaction of bacteriophage and bacterium is essential to acquisition of immunity to phage environmental factors induce changes in bactria; compete to adapt, survive, and thrive

Hfr conjugation

Conjugation involving an Hfr strain and an F- strain. *high frequency of recombination* -donor HFr cell has F factor integrated into its chromosome -donor genes are transferred to recipient cell -a complete copy of the F factor is usually not transferred -gene transfer can be clockwise or counterclockwise

Conjugation with Pilus

E. coli may or may not contain the F factor If F factor present Cell forms F pilus—serves as a donor of genetic information Copy of F factor is transferred from F+ cell to the F− recipient, converting the recipient to the F+ state

Place the steps involved in the process of bacterial transformation in the correct order.

*Bacterial transformation is a process in which a recipient cell takes up DNA from a lysed donor cell. The donor cell DNA can become part of the recipient cell chromosome if homologous recombination occurs in regions where the two types of DNA are similar.*

lytic cycle vs lysogenic - lytic

*new bacteriophages are made and the host cell is lysed.* Bacterial chromosome is degraded. Phage DNA is transcribed and translated to make new phage particles. Phage DNA is packaged into phage heads. Bacterial cell lyses, releasing phage particles.

lytic cycle vs lysogenic - lysogenic

*the phage DNA integrates into the host cell chromosome, and the phage DNA is replicated with the bacterial cell DNA as the cell divides.* Phage DNA is replicated along with the bacterial chromosome during cell division. Phage DNA is integrated into host cell chromosome. Bacterial cell survives and divides.

conjugation in bacteria

......type of bacterial recombination (create genetic diversity) in which one bacterium connects itself to another through a protein tube structure called a pilus. Genes are transferred from one bacterium to the other through this tube -Prototrophs result from two auxotrophs -Recombines at independent locations to become wild-type cells -Cell to cell contact is essential two auxotrophs recombine at indep locations to become prototrophs (wild type)

Bacteria Invade Antibiotics And Transform Into Superbugs

0 1 10 100 1000 100 10 1 0 - agar petri plate

Transduction: 3 observations used to identify the filterable agent (FA):

1. FA only produced when LA-2 cells grown in association with LA-22 cells 2. DNase did not make FA ineffective 3. When filter pore size below that of phages, FA could not pass through

Which of the following statements about cotransformation is true? A bacterial cell receives two adjacent genes on a single piece of DNA from the medium. The F factor plus a few chromosomal genes are passed from one cell to another. Nonlinked genes are passed simultaneously from one cell to another. Two bacterial cells within a culture are transformed by the same bacteriophage.

A bacterial cell receives two adjacent genes on a single piece of DNA from the medium.- This makes it possible to map pairs of genes that are located near each other.

*Fluctuation tests and the origin of adaptive mutations* One of the classic experiments of molecular genetics is the fluctuation test, which was developed by Salvador Luria and Max Delbr¨uck in 1943 to investigate the origins of adaptive mutations.

An adaptive mutation is one that increases the fitness (e.g., survival, fecundity) of an individual that carries that mutation. At the time, the molecular processes underpinning heredity and mutation were unknown (e.g., the structure of DNA was only described in 1951). There were two prevailing hypotheses explaining the origins of adaptive mutations: the spontaneous mutation hypothesis and the induced mutation hypothesis. According to the spontaneous mutation hypothesis, adaptive mutations occur by chance irrespective of the environmental conditions. According to the induced mutation hypothesis, adaptive mutations are directly induced by the environmental conditions in which they will be favored. Jay Taylor (ASU) Fall 2013 77 / 86 Fluctuation Tests Luria and Delbr¨uck developed an experimental system based on a bacterium Escherischia coli along with a virus (T1 bacteriophage) that infects it. When T1 phage is added to a culture of E. coli, most of the bacteria are killed, but a few resistant cells may survive and give rise to resistant colonies that can be seen on the surface of a petri dish. This shows that resistance to T1 phage is a trait that varies across E. coli bacteria and which is heritable, i.e., the descendants of resistant bacteria are usually themselves resistant.

Filterable Agent (FA)

Any of the infectious agents that pass through a filter of diatomite or unglazed porcelain with the filtrate and remain virulent and that include the viruses as presently understood and various other groups (as the mycoplasmas and rickettsias) which were originally considered viruses before their cellular nature was established.

prototrophs results from two ____________.

Auxotrophs

Benefits of using microorganisms in research

Bacteria and bacteriophages essential in genetic study Bacteria and virus research characteristics: -Exhibit extremely short reproductive cycles -Can be studied in pure culture

How do we know that during transduction bacterial cell-to-cell contact is not essential? Bacterial contact can be eliminated with a U-tube. Bacterial contact can be eliminated with a filter. This is a hypothesis.

Bacterial contact can be eliminated with a filter.

Prototroph

Can grow on minimal medium Can synthesize all essential organic compounds (human body can not) *wild type bacteria*

Which of the following statements about conjugation is true? Only competent cells can undergo conjugation. The F factor is an element that is found in the chromosome of an F+ cell. One strand of DNA from an F+ cell integrates into the chromosome of an F- cell, and the other strand is degraded. DNA is transferred from an F+ cell to an F- cell.

DNA is transferred from an F+ cell to an F- cell.

lysogenic phages

DNA phages that undergo adsorption and penetration but does not replicate (silent virus infection) Phages that can either replicate and cause cell lysis or can integrate their DNA into the host DNA are called; temperate phages

How do we know that bacteria undergo genetic recombination, allowing the transfer of genes from one organism to another? From experiments involving conjugation. From a variety of experiments involving transformation, conjugation, and transduction. From experiments involving transduction. From experiments involving transformation.

From a variety of experiments involving transformation, conjugation, and transduction.

Luria and Delbrück argued that the spontaneous and induced mutation hypotheses could be distinguished in the following manner:

If mutations are induced, then these will only appear after the bacteria are exposed to the phage. In this case, the number of resistant colonies will be approximately Poisson distributed and the variance will be approximately equal to the mean. If mutations are spontaneous, then the number of resistant colonies depends on timing of the mutation relative to the expansion of the culture. In this case, the variance will be much greater than the mean. The law of rare events explains why the number of resistant colonies is expected to be Poisson distributed under the induced mutation hypothesis: although there are a large number of cells that can independently mutate to the resistance phenotype, the probability of mutation was known to be low.

auxotroph

Needs complete medium Has lost ability, via mutation, to synthesize essential compounds *mutant* two auxotrophs recombine at indep locations to become prototrophs (wild type) ----> via conjugation

Transformation

Small pieces of extracellular DNA are taken up by bacterial cell Integrated stably into the chromosome *DNA is introduced into a cell and replicates

Which of the following is/are true of generalized bacteriophage transduction? The bacteriophage must enter the lysogenic cycle. The bacteriophage packages fragments of bacterial DNA into new phage particles. The bacteriophage chromosome has a region homologous to the bacterial chromosome.

The bacteriophage packages fragments of bacterial DNA into new phage particles. During transduction, phages package fragments of bacterial DNA into new phage heads. This bacterial DNA can be transferred to another bacteria cell during the next phage infection.

F factor (fertility factor)

The first plasmid observed to be transferred between cells during conjugation; is a plasmid, a double stranded closed circle of DNA Unidirectional transfer of genetic material F+ cells serve as DNA donors -F+ cells contain fertility factor -Confers ability to donate DNA during conjugation (has pili) F− cells are the recipients

heteroduplex

a DNA double helix composed of single strands from two different DNA molecules

spontaneous mutation

a random change in the DNA arising from errors in replication that occur randomly; creates genetic diversity and genetic variation

fluctuation test

a test used in microbes to establish the random nature of mutation or to measure mutation rates

lytic cycle

a viral reproductive cycle in which copies of a virus are made within a host cell, which then bursts open, releasing new viruses

Antibiotic-resistant bacteria are becoming an increasing problem. Some bacteria that were once killed by common antibiotics have acquired the ability to survive in the presence of those antibiotics. How can bacteria acquire antibiotic resistance? Select all that apply. Bacteria can gain an antibiotic-resistance gene by conjugating with another species of bacteria. Bacteria can acquire antibiotic-resistance genes by becoming infected with a virus that contains an antibiotic-resistance gene. Bacteria can acquire random mutations that allow them to grow in the presence of antibiotics. Bacteria can pick up an antibiotic-resistance gene from the environment through transformation.

all of them are true! Bacteria can acquire antibiotic resistance by a variety of methods, including random mutation and genetic transfer by transformation, transduction, or conjugation.

Transduction is a form of recombination in bacteria that involves ________. fertility factors plasmids bacteriophages 5-bromouracil physical contact between the bacteria involved

bacteriophages

How do we know that conjugation leading to genetic recombination between bacteria involves cell contact, which precedes the transfer of genes from one bacterium to another? involving a Davis U-tube: when the tube separated two auxotrophic strains, genetic recombination occurred involving a Davis U-tube: when the tube separated two auxotrophic strains, NO genetic recombination occurred involving a Davis U-tube and a filter: when the filter separated two auxotrophic strains, genetic recombination occurred involving a Davis U-tube and a filter: when the filter separated two auxotrophic strains, NO genetic recombination occurred

involving a Davis U-tube and a filter: when the filter separated two auxotrophic strains, NO genetic recombination occurred

3 growth phases of bacteria

lag .. slow growth log .. exponential growth stationary... plateau

Bacteriophages engage in two interactive cycles with bacteria. What are these cycles? negative and positive auxotrophic and prototrophic lytic and lysogenic heteroduplex and homoduplex insertion and replication

lytic and lysogenic

minimal medium (MM)

medium that contains only the nutrients required by prototrophic bacteria *prototrophs* Nutritional components simple Organic carbon source and inorganic ions

vertical gene transfer

occurs during reproduction between generations of cells; transfer of genetic info between same species.

temperate phages

phages that use both the lytic and lysogenic cycles

Sort each statement into the correct bin depending on whether it is true for conjugation only, transduction only, transformation only, or all three processes. Conjugation only Transduction only Transformation only All three I

problem

merozygote

recipient cell that is temporarily diploid as result of transfer process

Genetic Transformation (Dna transfer) horizontal mechs

results in altered genotype; mechanisms of genetic recombination/ variation. mech to genetic transfer of info 1. Conjugation 2. Transformation 3.Transduction

lysis

separation; destruction; loosening of cell wall

plasmid

small, circular piece of DNA located in the cytoplasm of many bacteria

Sort each statement into the correct bin depending on whether it is true for conjugation only, transduction only, transformation only, or all three processes. Conjugation only Transduction only Transformation only All three II

solution: Bacteria can acquire new genes from the environment through transformation, by direct contact with another bacteria cell through conjugation, or by being infected with a bacteriophage through transduction.

A symbiotic relationship between a phage and a bacterium apparently occurs in the process of lysogeny. t or f?

true

Cotransduction of genes is an indication that the genes are linked. True False

true

What is transduction? bacterial-mediated bacterial recombination bacterial-mediated viral recombination virus-mediated viral recombination virus-mediated bacterial recombination

virus-mediated bacterial recombination Correct Transduction is the process by which a virus accidentally picks up some bacterial chromosomal DNA and injects it into another bacterium, where recombination occurs.

bacteriophages (phages)

viruses that infect bacteria; Reproduce via bacterial genetic recombination mechanism: transduction

Bacteria Invade Antibiotics And Transform Into Superbugs II wild type survives and thrives.....

wild type accumulates successive mutations that leads to survival ; thus, bacteria that are normally not-resistant to an antibiotic eventually evolve resistance can evolve extremely high concentration tolerance after just 11 days (1000X)