virology lecture 10

most abundant biological entity on earth

bacteriophages

how many particles of bacteriophages infect a bacteria

15 to 25

how do bacteriophages play an important ecological role?

recycle carbon and organic matter

why do bacteriophages recycle carbon and organic matter?

so new life can be generated

bacteriophages have played an important role in understanding what since their discovery in 1915

molecular biology and genetics

what did the hershey-chase experiment in 1953 prove?

DNA is the genetic material, inherited from the parental phage, not protein

majority of bacteriophages contain a ___ and ___ structure

head and tail

what kinds of symmetry do bacteriophages have?

icosahedral or helical

word for the bacteriophages shape depending on environmental conditions

pleomorphic

two alternative lifestyles of bacteriophages for replication

lytic infection and lysogeny

look at slides 9 and 10

steps in bacteriophage lytic replication

adsorption, penetration, biosynthesis, assembly, release

what happens in the adsorption phase in bacteriophage lytic replication

attachment of phage to host cell

what happens in the penetration phase in bacteriophage lytic replication

nucleic acid penetrates host cell

what happens in the biosynthesis phase in bacteriophage lytic replication

phage gene expression and genome replication

what happens in the assembly phase in bacteriophage lytic replication

viral components assemble into progeny phage

what happens in the release phase in bacteriophage lytic replication

progeny virus releases from the infected cell

what part of the phage attaches to specific receptors on the bacterial cell wall

tail fibers

this is released from the tail fiber and digests a hole in the bacterial cell wall to allow DNA entry in phage adsorption (attachment)

enzyme (lysozyme)

adsorption (attachment) causes this kind of change, resulting in contraction of the tail sheath and penetration of the bacteriophage tail into the cell

conformational change

bacteriophage DNA or RNA genome is injected into the host cell through what part of the bacteriophage

tail tube

biosynthesis of bacteriophage lytic replication involves ______ and _______ of viral genes

transcription and translation

messenger RNA copied from viral DNA genes

transcription

mRNA template generates proteins on cell ribosomes

translation

a copy of the genomic DNA is reeled into this preassembled part of the bacteriophage

icosahedral head

steps of phage assembly 23

phage enzymes hydrolyze (break) bonds in the ________ of the bacterial cell wall, allowing the viruses to be released

peptidoglycan

steps in bacteriophage lysogenic infection

adsorption, penetration, integration, division **

do bacteriophages kill their hosts when they infect them in lysogeny

no

bacteriophage genome becomes _____ into a specific region of the host chromosomes during lysogeny infection

integrated

integrated bacteriophage genome

prophage

what is something that can induce the process of induction in lysogeny

environmental conditions

occurs when a dormant viral genome exits the host bacterial chromosome and switches to an active life cycle

process of induction in lysogeny

environmental conditions are favorable for bacterial and phage growth in this type of phage life cycle

lytic infection

environmental conditions are not favorable for bacterial and phage growth in this type of phage life cycle

lysogeny

phage elects to enter _____ (dormant state) until favorable conditions permit reactivation into the ____ _____

lysogeny, lytic cycle

type of lysogeny that occurs in human viruses

latency

the transfer of genes and genetic traits from one bacteria to another

genetic exchange

what could genetic exchange in bacteria result in?

increased pathogenicity, transfer of antibiotic resistance, evasion of host immune defenses

three modes of genetic exchange in bacteria

transformation, conjugation, transduction

mode of genetic exchange in bacteria involving an uptake of naked DNA (genes) through cell wall into bacteria

transformation

mode of genetic exchange in bacteria involving uptake of DNA through sex pili

conjugation

mode of genetic exchange in bacteria involving genetic exchange mediated by a virus

transduction

what are the two modes of genetic exchange by phage transduction

generalized and specific

type of transduction during lytic infection where a small piece of bacterial DNA is mistakenly packaged into a phage particle and transferred into a recipient cell

generalized transduction

type of transduction during lysogeny where phage DNA integrates into host bacterial chromosome and persists

specialized transduction

upon induction in specialized transduction, how does the prophage and host DNA genes get incorporated into a recipient cell

prophage exits incorrectly and takes along adjacent host DNA genes

occurs when a lysogenized bacteriophage increases the pathogenicity of a bacteria

lysogenic conversion

corynebacterium diphtheriae produces a toxin responsible for diphtheria if it carries this temperate bacteriophage

beta phage

this gene produces a toxin that causes diphtheria

phage tox gene

life threatening respiratory disease in children

diphtheria

how does the diphtheria vaccine work

induces antibodies that neutralize the toxin

what does the streptococcus bacterium secrete if it contains a temperate bacteriophage T2

pyrogenic or erythrogenic exotoxin

what does the toxin found in streptococcus cause

rash of scarlet fever

what must a lysogenic conversion have to cause infection

temperate bacteriophage

what are some diseases caused by lysogenic conversion

diphtheria, scarlet fever, cholera

severe gastrointestinal disease that includes excessive diarrhea, dehydration, and possible death

cholera

toxin expressed when the bacteria vibrio cholera contains a temperate bacteriophage CTXphi

cholera toxin

what does the cholera toxin do to the intestinal cells

causes them to secrete large amounts of water and electrolytes

bacteriophages are a potential therapeutic against what

antibiotic resistant bacteria

bacteriophage therapy

use of a specific bacteriophage that causes lytic infection of the drug resistant bacteria

what are some advantages of bacteriophage therapy

effective against antibiotic resistant bacteria, high specificity against target bacteria, cheaper to develop, side effects uncommon

why are side effects uncommon in bacteriophage therapy

phages do not infect human cells

what are some disadvantages of bacteriophage therapy

must identify specific phages, not effective against intracellular bacteria, more research needed

what are bacteriophages a threat to?

fermentation and pharmaceutical industries

what percentage of dairy product fermentation batches are lost to bacteriophage infection

1%-10%

what materials are contaminated with bacteriophages that causes the fermentation threat

raw starting materials

bacteria is used in a variety of food fermentation processes, including these foods:

yogurt, cheese, sauerkraut, soy sauce

pharmaceutical and biotechnology industries use bacteria on a large scale to produce products such as:

alcohols, vitamins, enzymes, antibiotics, amino acids, hormones

foodborne illness caused by the bacterium listeria monocytogenes

listeriosis

cocktail of six listeria bacteriophages in the form of an application spray

listex p100

listex p100 is used in clean rooms of dairy, meat, and poultry processing plants to inhibit the growth of this bacteria on products

listeria

what does CRISPR stand for

clustered, regularly, interspaced, short, palindromic, repeats

what are the two phases of CRISPR cas9

acquisition and immunity

phase in crispr cas9 where a bacterial cell is infected with a virus and specific viral DNA sequences are inserted in surviving bac

phase in crispr cas9 where the bacterial cell is infected with the same virus and Cas9 (bacterial enzyme that uses transcribed crispr RNA sequences as a guide) recognizes and cuts the virus DNA, inhibiting infection

immunity phase

what is CRISPR technology used for

edit DNA of bacteria, humans, animals, and plants