Tentative characterization of new environmental giant viruses by MALDI-TOF mass spectrometry.
OBJECTIVE
Metagenomic studies have revealed that Acanthamoeba polyphaga Mimivirus relatives are common in the environment; however, only three Acanthamoeba-growing giant viruses have been isolated from hundreds of environmental samples. We attempted herein to isolate new Acanthamoeba-growing giant viruses from environmental samples.


METHODS
We inoculated 105 environmental samples by our usual procedure but with the addition of selected antibiotics to inhibit bacterial overgrowth.


RESULTS
We isolated 19 giant viruses with capsid sizes of 150 to 600 nm, including one associated with a virophage. For the first time some were isolated from saltwater and soil samples. Tentative characterization using the PolB gene sequence was possible for some of these viruses. They were closely related to each other but different from the two previous isolates of Acanthamoeba polyphaga Mimivirus. Results obtained by MALDI-TOF MS analysis of viral particles were congruent with that of PolB sequencing.


CONCLUSIONS
Our data confirm that Acanthamoeba-growing giant viruses are common in the environment. Additionally, MALDI-TOF MS analysis can be used for the initial screening of new viruses to avoid redundant analysis. However, due to their genetic variability, it is likely that the genome sequences of most of these viruses will have to be determined for accurate classification.
La Scola
Bernard
B
Pôle des Maladies Infectieuses, Assistance Publique-Hôpitaux de Marseille and URMITE UMR CNRS-IRD 6236, IFR48, Faculté de Médecine, Université de la Méditerranée, Marseille, France. bernard.lascola@univmed.fr
Campocasso
Angélique
A
N'Dong
Rolande
R
Fournous
Ghislain
G
Barrassi
Lina
L
Flaudrops
Christophe
C
Raoult
Didier
D
D000048:Acanthamoeba / Q000821:virology*; D002213:Capsid / Q000648:ultrastructure; D016000:Cluster Analysis; D004257:DNA Polymerase II / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics; D004783:Environmental Microbiology; D056686:Mimiviridae / Q000235:genetics; D010802:Phylogeny; D017385:Sequence Homology; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014764:Viral Proteins / Q000235:genetics; D014780:Viruses / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure*
D004279:DNA, Viral; D014764:Viral Proteins; D004257:DNA Polymerase II