Bacterial and Archaeal Viruses

Question 1

Describe bacteriophage landing

Answer 1

Single central tail fibre called adhesion or cluster of tail fibers mediate reversible bacterial cell adhesion

Question 2

Describe bacteriophage pinning

Answer 2

Irreversible binding of secondary tail protein to cell surface molecule of bacterium

Question 3

Describe bacteriophage entry

Answer 3

Tail contraction and cell membrane penetration

Question 4

Describe bacteriophage DNA injection

Answer 4

Mediates genome viral insertion into host cell

Question 5

Describe bacteriophage replication

Answer 5

100-300 daughter phages in as little as 30 minutes

Question 6

Describe bacteriophage bursting

Answer 6

Lysis of host cell releasing crop of phages

Question 7

What are the two bacteriophage life cycles? Describe each.

Answer 7

Lytic: when the bacteriophage will replicate within the cell and burst to repeat the cycle
Lysogenic: when the phage is replicated along with bacterial DNA which continues indefinitely.

Question 8

Why are bacteriophages ideal?

Answer 8

They attack only bacterial cells - not host cells
Very narrow host range of species/strain
Fast mutation rate
Infections are self-limiting

Question 9

Describe phage therapy.

Answer 9

Targeted use of lytic phages to destroy pathogenic bacteria in food, therapeutics, agriculture, and the environment

Question 10

How can bacteriophages be used as biosensors?

Answer 10

Probes for sensitive and selective detection of pathogens via GM phages and can enhance knowledge on phage receptor binding proteins.

Question 11

Give a brief description of the bacteriophage T7

Answer 11

Linear dsDNA genome
Naked icosahedral capsid
Short tail fibers
56-59 proteins
Smallest bacteriophage

Question 12

How are bacteriophage T7’s genes classified?

Answer 12

With decimal numbers and under classes early, middle, and late (class I, II, and III)
Class 1 - controls phage and host gene expression
Class 2 - phage DNA replication
Class 3 - structure, assembly, and host cell lysis

Question 13

How does T7 phage interact with a bacterium?

Answer 13

binds to LPS using tail fibers. GP16 degrades peptidoglycan layer by boring a hole and transports the first part of the genome through the host cell. Full entry is powered by transcription by the host RNA enzyme

Question 14

Which protein does the T7 phage use to assemble in cytoplasmic membrane and create a pore for virus release?

Answer 14

Holin

Question 15

Give a brief description of archaeal viruses in general

Answer 15

DNA viruses (only two ssDNA)
External OR internal lipid envelopes
Most do not encode a DNA polymerase
Many don't cause cell lysis b/c of environment
Most viral genes are of unknown function

Question 16

Briefly describe fuselloviridae

Answer 16

Affecting family Crenarchaeota
Tail used to attach to surfaces
Genome integrated into tRNA gene of host chromosome
Produce virus in stressful condition
Doesn't kill host cell

lemon shaped with tail filament, enveloped, dsDNA w 34 genes, positive supercoil, capsid protein VP1, contains INTEGRASE

Question 17

What is the prototypic fuselloviridae?

Answer 17

SSV1

Question 18

Briefly describe the replication of SSV1

Answer 18

Attachment, injection, viral gene integration, transcription and traduction of early genes, replication of DNA, transcription and traduction of late genes, genomic DNA packaged, mature virions released by budding.

Question 19

Where is SSV1 living in nature?

Answer 19

Hot springs

Question 20

What does SSV1 have at a molecular level to keep it safe in its natural environment?

Answer 20

Disulfide bonds in the proteins which help to resist heat in the hot springs in which it lives.

Question 21

How is SSV1 episomal DNA found in the host?

Answer 21

3 forms:
Positively supercoiled - for packaging
Negatively supercoiled - for genome replication
Relaxed double stranded - for translation

Question 22

Does SSV1 need integrase?

Answer 22

No, it can be dispensed but it IS positively correlated with increased fitness.

Question 23

Does SSV have a satellite virus?

Answer 23

Yes! pSSVx

Question 24

What is a CRISPR locus? What does it do?

Answer 24

An anti-viral mechanism in bacteria and archaea. It recognizes portions of viral genomes which it has seen previously and it will cleave the DNA. Like bacterial immune systems.