Bacterial and Archaeal Viruses Flashcards
Describe bacteriophage landing
Single central tail fibre called adhesion or cluster of tail fibers mediate reversible bacterial cell adhesion
Describe bacteriophage pinning
Irreversible binding of secondary tail protein to cell surface molecule of bacterium
Describe bacteriophage entry
Tail contraction and cell membrane penetration
Describe bacteriophage DNA injection
Mediates genome viral insertion into host cell
Describe bacteriophage replication
100-300 daughter phages in as little as 30 minutes
Describe bacteriophage bursting
Lysis of host cell releasing crop of phages
What are the two bacteriophage life cycles? Describe each.
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.
Why are bacteriophages ideal?
They attack only bacterial cells - not host cells
Very narrow host range of species/strain
Fast mutation rate
Infections are self-limiting
Describe phage therapy.
Targeted use of lytic phages to destroy pathogenic bacteria in food, therapeutics, agriculture, and the environment
How can bacteriophages be used as biosensors?
Probes for sensitive and selective detection of pathogens via GM phages and can enhance knowledge on phage receptor binding proteins.
Give a brief description of the bacteriophage T7
Linear dsDNA genome Naked icosahedral capsid Short tail fibers 56-59 proteins Smallest bacteriophage
How are bacteriophage T7’s genes classified?
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
How does T7 phage interact with a bacterium?
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
Which protein does the T7 phage use to assemble in cytoplasmic membrane and create a pore for virus release?
Holin
Give a brief description of archaeal viruses in general
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
Briefly describe fuselloviridae
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
What is the prototypic fuselloviridae?
SSV1
Briefly describe the replication of SSV1
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.
Where is SSV1 living in nature?
Hot springs
What does SSV1 have at a molecular level to keep it safe in its natural environment?
Disulfide bonds in the proteins which help to resist heat in the hot springs in which it lives.
How is SSV1 episomal DNA found in the host?
3 forms:
Positively supercoiled - for packaging
Negatively supercoiled - for genome replication
Relaxed double stranded - for translation
Does SSV1 need integrase?
No, it can be dispensed but it IS positively correlated with increased fitness.
Does SSV have a satellite virus?
Yes! pSSVx
What is a CRISPR locus? What does it do?
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.
