Lecture 18 - Marine Viruses Flashcards
Give and describe the two most abundant marine cyanobacteria.
Prochlorococcus - small cyanobacteria. Dominates in ocean gyres and nutrient-limited areas.
Syenochococcus - dominates in coastal regions, polar and higher latitude areas. Alter their pigmentation, enables them to photosynthesise at different depths.
What is the cyanobacteria most often seen in the oceans?
Prochlorococcus
What is the most dominant group of heterotrophs?
SAR11.
Some of smallest free-living cells - fits through a .2-micron filter.
Lives in low nutrient conditions.
What percentage of bacteria found in oceans at any given point is SAR11?
30-50%
Give the steps to the marine carbon cycle.
1) Phytoplankton produce carbon.
2) Phytoplankton die and sink, forming POM.
3) Phages infect phytoplankton, lyse cells open producing DOM (Dissolved Organic Matter).
4) Bacteria feed on DOM produced by phages.
5) This forms CO2 which is released back into the atmosphere.
What is the size of the average marine virus?
50nm
How do viruses meet host cells?
Through probability
How many viruses are there per ml of seawater?
10 million
When does abundance of viruses decrease?
- With depth
- With distance from the shore
Because there is less to feed on.
For every microbial cell on the surface, how many viruses are associated with it?
10
What is the second largest component of biomass (after bacteria and archaea)?
Viruses.
If all marine viruses are lined up, what would be the distance they would reach?
73 million light years
What are the three most studied groups of marine phages?
- Podoviridae
- Siphoviridae
- Myoviridae
Describe
a) Podoviridae
b) Siphoviridae
c) Myoviridae
a) Podoviridae = short tails.
b) Siphoviridae = long, non-contractile tails.
c) Myoviridae = contractile tails.
Which marine phage resembles T4?
Myoviridae.
Why are the most-studied marine phages double-stranded DNA viruses?
They are easiest to sample, can be sequenced easily.
Extracting RNA from seawater is also difficult.
What might viruses have initially evolved?
Nuclei
Describe the lysogenic infection of a virus.
Insertion of a virus into the genome of the host, into a tRNA, acting as a prophage.
As host replicates, produces a second copy of the virus.
An environmental change leads to increased abundance of the host.
Virus detects an increase in abundance and switches to lytic cycle.
Splits open host cell to meet new hosts.
What is the viral shunt?
Keeping carbon within a bacterial loop, preventing it from reaching higher trophic levels.
What percentage of microbes at any given time are infected by viruses?
30%
What percentage of microbes are killed each day by viruses?
20%
What percentage of carbon in the ocean goes through the viral shunt?
25%
What are auxiliary metabolic genes?
Viral versions of host genes used to hijack host metabolism to improve infection.
Give three examples of auxiliary metabolic genes.
- psbAD; increases photosynthesis.
- mazG; inhibits stringent response (alerting nearby microbes).
- pstS (increases phosphate uptake).
Why is pstS useful for increasing phosphate uptake?
Because viruses need more phosphate than the host cell would normally be able to supply.
How do phototrophs infected with psbAD respond?
Decrease carbon fixation.
Products from PSII increase, but never make it to light-independent reactions. Instead are funnelled into viral production.
What is the Kill-the-Winner hypothesis?
That infection rates are impacted by host abundance and resistance.
How do viruses increase in the genetic diversity of microbes?
With no viruses, evolution of bacteria gives it a selective advantage, allows alleles to go to fixation.
With viruses present, microbes die after reaching a certain abundance, therefore they remain very diverse.
What percentage of marine bacteria are amenable to culturing?
1%
What is metagenomics?
Collecting viral community DNA, sequencing it, and reconstructing their genomes.
How much DNA is required for any sequencing to be conducted?
20 nanograms
What is added to water for viral DNA to be collected?
Iron chloride.
Water precipitates out, viruses come together.
