Kristen Belanger
February 16, 2009
Acanthamoeba polyphaga
•  One of a group of free-living amoebae that
can be found in a variety of environments
-soil, seawater, dust, vegetation, airconditioning units, swimming pools
•  Amphizoic amoebae: can survive freely in
nature, or inside mammalian hosts
Acanthamoeba polyphaga
Mimivirus
•  Mimicking microbe
•  Very large, mature viral particles are 400nm
•  Unenveloped, icosahedral capsid
-multilayered membrane
•  80nm fibrils attached to the capsid
•  dsDNA linear genome, 1.2 Mbp in size
Giant Virus
La Scola, B, et al. A Giant Virus in Amoebae 10.1126/science.1081867
APMV viral particles and viral factory
Raoult, D. et al. Redefining viruses: lessons from Mimivirus doi:10.1038/nrmicro1858
Sputnik invades APMV viral factories
and viral particles
La Scola, B. et al. The virophage as a unique parasite of the giant mimivirus doi:10.1038/nature07218
Sputnik propagation in Mamavirusinfected amoebae
La Scola, B. et al. The virophage as a unique parasite of the giant mimivirus doi:10.1038/nature07218
Presence of Sputnik does not affect Mamavirus Multiplication Cycle
La Scola, B. et al. The virophage as a unique parasite of the giant mimivirus doi:10.1038/nature07218
Sputnik causes production of defective Mamavirus particles
La Scola, B. et al. The virophage as a unique parasite of the giant mimivirus doi:10.1038/nature07218
Abnormal Mamavirus Particles
have Decreased Pathogenicity
La Scola, B. et al. The virophage as a unique parasite of the giant mimivirus doi:10.1038/nature07218
ORF Homology
ORF Homologues
Blue = Mamavirus/Mimivirus
Green = NCLDV’s and Bacteriophage
Red = Archaeal virus gene
Gray = ORFan
Purple = Virion protein coding sequences
La Scola, B. et al. The virophage as a unique parasite of the giant mimivirus doi:10.1038/nature07218
La Scola, B. et al. The virophage as a
unique parasite of the giant mimivirus
doi:10.1038/nature07218
Gene (size,
amino-acid
residues)
Closest homologue in GenBank
nr
Domain architecture/protein
family/predicted activity
Predicted function in
virophage replication
ORF 1 (144)
–
Unknown
Unknown
ORF 2 (114)
–
Unknown
Unknown
ORF 3 (245)
RecA-superfamily ATPases (Actinobacillus
pleuropneumoniae serovar 1 str. 4074)
FtsK–HerA superfamily ATPase
DNA packaging
ORF 4 (139)
Limited similarity to diverse Zn-ribbon proteins
Zn-ribbon-containing protein
Transcription regulation?
ORF 5 (119)
–
Unknown
Unknown
ORF 6 (310)
MIMI R196
Collagen triple-helix-repeat-containing
protein
Protein–protein interactions in
factories
ORF 7 (236)
C1q and tumour necrosis factor related protein
5, mouse
Collagen triple-helix-repeat-containing
protein
Protein–protein interactions in
factories
ORF 8 (184)
–
Unknown
Minor virion protein
ORF 9 (175)
–
Unknown
Unknown
ORF 10 (226)
Phage integrase family protein (Methanococcus
aeolicus Nankai)
Tyr recombinase family integrase
Integration of virophage into APMV
genome?
ORF 11 (162)
–
Unknown
Unknown
ORF 12 (152)
MIMI R546
Unknown
Unkown
ORF 13 (779)
Putative DNA-polymerase or DNA-primase
(Lactobacillus phage phiadh)
Primase–helicase
DNA replication
ORF 14 (114)
–
Zn-ribbon-containing protein
Transcription regulation?
ORF 15 (109)
–
Membrane protein
Modification of APMV membrane?
ORF 16 (130)
–
Unknown
Unknown
ORF 17 (88)
–
IS3 family transposase A protein
DNA-binding protein
ORF 18 (167)
–
Unknown
Unknown
ORF 19 (218)
–
Unknown
Minor virion protein
ORF 20 (595)
–
Unknown
Major capsid protein
ORF 21 (438)
–
Unknown
Unknown
La Scola, B. et al. The virophage as a unique parasite of the giant mimivirus doi:10.1038/nature07218
Acanthamoeba is a Melting Pot
•  Many amoeba phagocytose bacteria for
‘food’
•  Some bacteria can evade digestion by the
amoeba and even multiply within them
Enteropathogenic E. coli
Enterococcus faecalis
Salmonella typhimurium
Bacillus cereus
Huws, S. et al. Interactions of some common pathogenic bacteria with Acanthamoeba polyphaga
doi:10.1111/j.1574-6968.2008.01123.x
Chicken or the Egg
•  Did Sputnik and Mimivirus give genes to
Acanthamoeba or did they get genes from
Acanthamoeba?
•  Could Mimivirus have been a
bacterium at one time?
Was Sputnik originally a bacteriophage?
Should viruses be considered alive?
•  Wikipedia: life is a condition that distinguishes
organisms from inorganic objects
-life is a characteristic of self organizing, self
recycling systems consisting of populations of
replicators that are capable of mutation, around
most of which homeostatic, metabolizing
organisms evolve
•  Webster: life is the period during which
something is functional
What if?
What if Chlamydia
trachomatis, an
obligate intracellular
organism, evolved to
no longer have
ribosomes?