Micro Chapter 8

Temperate phage

ordinarily does not cause a disruptive infection (lysogenic cycle)

Initiating Segment

part of the F plasmid is transferred along with adjacent chromosomal genes (F- recombinant)= 3

High-frequency recombinations

(a) conversion of F+ cells to Hfr condition - Hfr cells arise from F+ cells when their F plasmid is incorporated into a bacterial chromosomes at one of several sites (b) During conjugation, the initiating site of the F plasmid and adjacent genes are transferred to a recipient cell - genes are transferred in linear sequence, and the number of genes transferred depends on the duration of conjugation and whether the DNA strand remains intact or breaks -Hfr= no longer a male b/c males have to have a separate plasmid - after Hfr conjugates with an F-, the F- undergoes recombination and becomes F- recombinant (F- cell with some quantity of chromosomal DNA

Transformation

- A change in an organisms characteristics because of transfer of genetic information - Naked DNA - Competence factor is released into the medium and facilitates the entry of DNA into cell - DNA transport proteins and DNA exonuclease (an enzyme that cuts up DNA) is also needed

Transduction

- A method of transferring genetic material using a bacteriophage - Phage capable of infecting a bacterium attaches to a receptor site on the cell wall

Recombinant DNA technology

- Making recombinant DNA involves three process: 1. Manipulation of DNA in vitro (test tube) 2. Recombination of another organisms DNA with bacterial DNA in a phage or a plasmid (vector) 3. The cloning, or production of many genetically identical progeny, of phages or plasmids that carry foreign DNA - vivo=in the cell

Lysogenic cycle

- The phage is replicated along with the bacterial DNA prior to binary fission - No viral replication - Binary fission is completed; each cell has the phage DNA incorporated

producing recombinant DNA

- find the gene of interest - cut it out (cleave it) by using restriction enzymes - insert the foreign DNA into another chromosome - attach by using DNA ligase (forms covalent bonds between sugar and phosphate) - this creates the recombinant plasmid which is inserted into a new cell and that cell begins to replicate

Specialized transduction by lambda phage in e. coli

- phage DNA inserts itself into the bacterial host chromosome at a particular site -when the phage DNA replicates, it takes bacterial genes from either side of the site and packages them with its own DNA into new phages - only genes adjacent to the insertion site, not genes from other parts of the host chromosome, are transduced - These genes can then be introduced into the phages next host cell, where they will confer new genetic traits

The formation of F' plasmids

- when the F plasmid in an Hfr cell separates from the bacterial chromosome, it may carry some chromosomal DNA with it and thus creates the F' plasmid within a F' cell

The transfer of F plasmids

-F plasmids are circular, double-stranded DNA molecules - F+ cells contain F (fertility) plasmids and makes the F pilus (male/ donor) - F- cells lack F plasmids (female) - F+ pilus (sex pilus): A conjugation pilus bridge which attaches to the F- cell

Bacterial transformation

-Genes (naked DNA) from dead cell A enter into cell B -Cell B undergoes recombination -The DNA that is not recombined is broken down by enzymes

An F+ X F- mating

-The F+ (donor cell) transfers one strand of DNA from the F plasmid to the F- (recipient cell) via the conjugation bridge -As this occurs, the complementary strands of F plasmid DNA are synthesized. - Thus, the recipient cell gets a complete copy of the F Plasmid, and the donor cell retains a complete copy -Both cells then become F+

Lytic cycle

-The phage DNA directs the cell's metabolism to produce viral components- proteins and copies of phage DNA and protein coat -empty phage heads are synthesized - Heads are packed with DNA - Collars, sheaths, and base plates have been attached to heads. Tail fibers are added last - Bacterial cell lyses, releasing completed infective phages - And the cycle continues

General Transduction

-bacteriophage inserts its DNA into CellA -Bacterial DNA is fragmented as phage replicates - Fragment of bacterial DNA is incorporated into phage head. Bacterial cell is lysed, and new phage is released - Phage containing bacterial DNA infects cell B - genes from the first bacterial host are incorporated into chromosome of new host (cell B)

Bacteriophage life cycle

-phage attaches to receptor site on another bacterial cell wall, penetrates it, and inserts its DNA -The phage DNA inserts itself (as a prophage) into bacterial chromosome - It then becomes a part of the lytic cycle or the lysogenic cycle

Generalized transduction

1. Bacteriophage infection of a host bacterium initiates the lytic cycle (A) 2. Chromosome is broken into fragments which can be picked up and packed up with phage DNA 3. Particles are released and infect another bacterial cell (B on chart) 4. Host acquires genes that were brought along (transduced) from the previous cell

Results

1. F+ + F- = F+ all 2. F+= Hfr 3. Hfr= F- recombinant 4. Hfr= F+ 5. Hfr= F' (with some duplicate gene pairs; one on chromosome, one on plasmid - 1 and 3 are conjugating

High- frequency recombinations (Hfr)= 2

Can induce more than 1000X the number of genetic recombinations seen in F- and F+ -Hfr strains arise from F+ strains when the F plasmid is incorporated into the bacterial chromosome at one of several possible sites - When an Hfr cell serves as a donor in conjugation, the F plasmid initiates transfer of chromosomal DNA

The transfer of F' Plasmids

DNA incorporated into a chromosome (Hfr) can separate from it and again become an F plasmid (F+)= 4 - in some cases this separation occurs imprecisely, and a fragment of the chromosome is carried with the F plasmid - cells containing such plasmids are called F' strains (partial diploid cell (F' not F+ because only a part of the F plasmid is transferred))= 5

Naked DNA

DNA that has been released from an organism after the cell has been lysed and DNA is no longer incorporated into chromosomes

Prophage

DNA that is incorporated into the host bacterium's DNA

Conjugation

F+ or male is the one that makes the bridge to the F- or female

Conjugation

Genetic info is transferred from one cell to another (an example of horizontal gene transfer)- both cells are ALIVE - Conjugation differs from the other mechanisms in two ways 1. It requires contact between donor and recipient cells (females) 2. It transfers much larger quantities of DNA - occasionally whole chromosomes can be transferred

Who discovered transformation?

Griffith

Horizontal (lateral) gene transfer

Pass genes to other microbes of their same generation

Lysogeny

Persistence of a prophage without phage replication and destruction of bacterial cell (lysogenic cycle)

Specialized transduction

Several lysogenic phages are known to carry out specialized transduction - Lambda phage in E. coli has been studied - Phages usually insert at a specific location when they integrate with a chromosome (near the site of the prophage) - Lambda phage inserts into the E.coli chromosome between the gal gene (galactose) and the bio gene (biotin)

Recombination

The combining of genes (DNA) from two different cells

When heat-killed smooth pneumococci, with capsule and live, rough pneumococci, without capsule are both injected into the mouse....

The mouse dies because live smooth pneumococci plus live rough pneumococci are isolated from the dead mouse

When heat-killed smooth pneumococci, with capsule is injected into the mouse...

The mouse lives

Protoplast fusion

is accomplished by enzymatically removing the cell walls of organisms of two strains and mixing the resulting protoplasts

Transposable element

a mobile genetic sequence

Transposon

a transposable element that contains genes for transposition

Bacteriophage

a virus that can infect bacteria

Genetic Fusion

allows transposition of genes from one location on a chromosome to another

Virulent Phage

capable of causing infection and the destruction and death of a bacterial cell (lytic cycle)

Virulence Plasmids

carry genes that cause disease

Resistance Plasmids

carry genes that provide resistance to various antibiotics

Tumor-inducing plasmids

cause tumor formation in plants (Ti plasmids- primarily for to affect plants)

Phages

composed of a core of nucleic acid covered by a protein coat

Some plasmids

contain genes for catabolic enzymes

Other Plasmids

direct the synthesis of bacteriocidal proteins called bacteriocins

F Plasmids

direct the synthesis of proteins that self-assemble into conjugation pili

Gene Transfer

refers to the movement of genetic information between organisms

Genetic engineering

refers to the purposeful manipulation of genetic material to alter the characteristics of an organism in a desired way

Transposition

the ability of a genetic sequence to move from one location to another

When live, virulent, smooth pneumococci (s-type), with capsule is injected into the mouse....

the mouse dies

When live, nonvirulent, rough pneumococci (r-type), no capsule is injected into mouse...

the mouse lives

Insertion sequence

the simplest type of transposable element

Mechanisms of lateral gene transfer in bacteria

transformation, transduction, and conjugation

Vertical gene transfer

when gene passes from parents to offspring