Bacteriophages

The stx1 and the stx2 genes are on phages (E. coli). What strictly controls them? When repressed, what is the transcription of the prophage going to be blocked by? How is induction going to happen?

"late" phage promoters Blocked by a Cl repressor Induction is going to happen when the repressor is cut upon environmental stimuli

In which two lysogenic processes do bacteria and phages cooperate with eachother?

- lysogenic conversion - active lysogeny

What natural factors are restricting widespread application of phage?

- narrow host range -temperate lifestyle -slow multiplication and killing - resistance - occurance, selection, possible developments -potential: undesired genetic element transfer potential

What are some examples of phenotypic alterations due to lysogenic conversion which help the bacteria: adapt to the environment enhance fitness

- provide phage insensitivity -stress tolerance . virus dissemination & spread

What are some examples of phenotypic alterations due to lysogenic conversion which help the bacteria: virulence and pathogenicity factors

-toxin production -host attachment factors (that enable colonization in the host) -invasion associated proteins & factors for intracellular survival

What are 4 main classes of phage therapy?

1. phage therapy (gene insertion, killing) 2. phage enzymes 3. biofilm dispersal 4. drug sensitization

The stx1 and the stx2 genes are on which phages? (E. coli)

933W H-19B and lambda

With E. coli intoxication, the you only get symptoms if there is a lot of shiga-toxin which was produced. How is the shiga toxin production going to be amplified?

A STEC cell can release the stx transducing phage This can convert non-toxigenic E.coli into toxic.

Recall the Shiga-toxin. What type of toxin is it? What does it inhibit?

A:B5 toxin which inhibits protein synthesis

What type of toxin is the cholera toxin (Ctx)

A:B5 type

What is the theory behind active lysogeny?

An integrated prophage serves as a regulatory switch that controls the expression of bacterial genes.

What phage is the cholera phage

CTX

Once the cholera toxin (Ctx) is in the cytoplasm, what is going to happen. What does this lead to. Describe the process.

CTx-A1 1. cleaves NAD+ to ADPR (ADP-Ribose) 2. modifies cellular regulator protein Gs to ADP-Ribosyl Gs 3. AC (adenylate cyclase) transforms ATP in cAMP The high cAMP levels lead to massive secretion of Cl- and K+ into the gut mucosal cells THEN large volumes of liquid and co-transported ions are secreted into the lumen of the small intestines. Water cannot be reabsorbed by the large intestine Leads to extreme water diarrhea (rice water stool) - up to 24 L/ day of water loss

What are tailed phages going to be called?

Caudovirales

What types of phages are most often isolated from the environment?

Caudovirales

How are phages involved with E. coli?

Certain Shiga toxin genes are carried on phages

For the German H104:H4 outbreak... what type of E. coli is it?

EAHEC from EHEC and EAEC

With regards to the phage-regulatory switch of active lysogeny.. . where is it integrated? Why is this significant?

Integrated within the open reading frame (or adjacent region, i.e. affecting the promoter). the expression of the gene is deactivated the gene is restored when the prophage is excised

The T3SS- what does it do? What is its function going to be?

It is going to be able to inject virulence factors into Eukaryotic host cells

With phages, what is generalized transduction going to be?

It is when the phage accidentally takes up some of the host DNA and not its own? And then it infects it into another cell and cannot replicate.

What are pathogenicity islands?

Loci of chromosomes with large groups of genes which encode virulence factors

Gifsy-1 is a phage which infects which bacteria?

Salmonella

How are phages involved with Clostridium botulinum?

Serotype C1 and D are carried by phage, Type E can be moved by a helper phage. Basically, just know that phage presence is needed for the toxin production

How are phages involved with Vibrio cholerae?

The cholera toxin is going to be carried on a phage that can also replicate as a plasmid

With phages, how does transformation occur?

The phages are released (after cell lysis) and go on to infect another cell

For the toxigenic V. cholerae, typically there are prophages which are inserted near the terminus of the larger of the two Vibrio chromosomes. What does this enable?

The promoter can be independently activated.

What does the term "lysogenic conversion" actually describe?

The specific phenotypic changes mediated by the "foreign" phage-transferred genes

Describe the general principle behind lysogenic conversion

This is like the standard transformation, except the phage encodes for toxin production. The toxins can either be secreted or released during bacterial lysis.

What happens when expression occurs during lysogeny? What is the alternative?

Virulence factors are expressed from the lysogenic prophages Secreted by the bacterial secretion systems The alternative is when there is a subpopulation which switches to the lytic cycle. The virulence factors which the phage encodes for are going to be released by diffusion. Remaining cells, which are alive, invade the mammalian cell and propogate with them. The lytic population is sacrificed to benefit the other bacteria in the population

For the host cells, what does lysogeny/lysogenic conversion usually result in? What can it result in, that has the potential to have negative consequences?

a special advantage or benefit some bacteria can undergo lysogenic conversion and cause disease (i.e. the pathogens have conferred the benefit of survival in our bodies)

What three things is phage specificity based on?

attachment gene expression interference

What is another word to describe temperate?

benign

What is a phage called that cannot produce viable progeny?

cryptic phages

Gifsy-1 phage carries what type of gene? What protein does this gene encode for? What secretion systems transport the protein out of the cell?

gog GogB SPI-1 and SPI-2 encoded type III

Talking about the A511 phage engineered for Listeria detection... how is the DNA integrated into the genome?

homologous recombination

What is the most important mechanism in the evolution of bacterial pathogenicity?

horizontal transfer of virulence genes

When can genes carried by phages potentially be expressed?

in the lysogenic cells - during the dormancy of the silent prophage or immediately after induction into the lytic cycle

If you call phages pathogens, what type of pathogens are they?

indirect

How is the CTX phage going to enter the Vibrio cholerae? What happens once it is integrated into the bacterial chromosome? Why does this only happens in humans?

it forms pili formed through the expression of the TCP type-4 bundle -forming pilus gene as receptors one integrated, the ctx genes on the phage are activated by the same ToxR regulator that turns on TCP expression this only happens in our body when the bacteria produce pilli and then this enables the Cholera in order to colonize

What is a reporter phage?

it is a phage that uses the biological specificity of the phage infection process and using this to detect certain bacterial cells (after the bacterial cells are expressing genes that have been introduced into the genome)

In which cycle do the cells lyse.... lytic or lysogenic?

lytic

What natural environments is Bacterial luciferase going to come from?

marine environments

What is a killer phage?

mean to kill infected bacterial cells- creating progeny is not the goal

E. coli virulence factors are encoded on what...

mobile genetic elements

What type of phages have narrow host ranges? What type of phages have broad ranges?

narrow - temperature phages broad - virulent phages

Does phage detection of cells detect live or dead bacteria?

only live

When using reporter phages, why is there no need to purify the organism before detection?

only susceptible hosts are infected

An integrated prophage serves as a regulatory switch that controls the expression of bacterial genes. What is this called?

phage regulatory switch

What are the most abundant self-replicating units on earth.

phages

In Vibrio when the phage and cholera toxin are co-released, what released them and what type of secretion system is this?

secretin EpsD type II secretion system the phage bascially hijacks the cholera cells and the transport system without killing it.

Stx =

shiga toxin

Recalling the structure of the cholera toxin (ctx).... which part of the toxin is going to be the receptor binding complex? why does it bind to? why is this significant?

the B sub-units are the receptor binding complex binds to GM1 membrane gangliosides on enterocytes Allows for transport of the toxin in the host cell cytoplasm

When the CTX phage is induced, what happens?

the cell is not lysed rather, the phage and cholera toxin molecules are co-released.

What is a prophage made of?

the genetic material of a bacteriophage, incorporated into the genome of a bacterium and able to produce phages if specifically activated

What are bacteriophages?

they are viruses which infect bacteria

T3SS =

type III secretion systems