lecture 11

Question 1

 Halophilic virus

Answer 1

• Found in high density in hypersaline ponds
• 10^-7 to 10^-9 particles/ml
• Lemon shaped, head-tail morphology
• All double stranded linear DNA
  OR
• Alkaline lakes
• Double stranded DNA, large range of genomes (14kb to 400kb in size)

Question 2

 Extreme thermal viruses

Answer 2

1) High diversity
2) High morphological diversity e.g. lemon/rod structures
3) Broad spectrum of bacterial hosts
4) Poorly studied

Question 3

PAV1

Answer 3

o Best characterised virus
o Host: Pyrococcus abyssi
o 18Kb circular DNA and no similarity to any other viral genomes
o Application: Producing thermal enzymes in industry

Question 4

STIV

Answer 4

o No homology to other viral genomes
o Replication process is unknown
o Capsid proteins are like mammalian adenoviruses
o Complex arrangement of capsid proteins not seen in other bacterial viruses (predominantly beta-sheets) and probably formed by a lipid envelope
o Similarities to modern adenoviruses due to: 1) convergent evolution (analogous structures which were not seen in last common ancestor but have same/similar function) 2) Horizontal gene transfer

Question 5

 Other extreme viruses

Answer 5

1) Polar environment:
- 10^-8 particles/ml on ice surface but 10^-6 on sea water
- All double stranded linear DNA

2) Deep surface environment:
- Found in oceanic drilling programme
- 10^-9 particles/cm3 n depths of 1,000 where there is a high abundance of bacteria
- Double stranded DNA
- Large diversity but none fully characterised
- Found using metagenomic analysis

Question 6

3) Thermophylic archaeal virus (BSL RDHV)

Answer 6

• rod structure and a single protein APBV1 which is in a circular formation. Contains a-helix dimer
• Protrusions at tip= suggests proteins can be glycosylated
• Glycans hook onto host for membrane entry
• Pointed cap structure involved in recognition of the host receptor proteins
• Found in Boiling Spring Lake located in Lassen volcanic national park, USA.
• Lake is acidic (pH 2.5), high temperature from 52C to 95C
• Capsid phenology and replicase put BSL RDHV in both DNA and RNA viruses
• Capsid structure for resides 156 to 302 of virus identical to Tomato Bushy Stunt (RNA virus) but do not know who transferred to who
• Circovirus-like DNA genomes whose common ancestor incorporated a capsid protein gene known previously only in RNA viruses

Question 7

summary

Answer 7

Extreme virus show a genomic diversity much greater that viruses from any other know environment
Most of these viruses are not characterized
All known extreme viruses are dsDNA, only a few reported to be RNA based but with “hybrid” charactersitics
More than 85% of viral sequences from extreme viruses has not homology to other known proteins