Complete genome sequence of Tunisvirus, a new member of the proposed family Marseilleviridae.

Marseillevirus is the founding member of the proposed family Marseilleviridae, which is the second discovered family of giant viruses that infect amoebae. These viruses have been recovered from environmental water samples and, more recently, from humans. Tunisvirus was isolated from fountain water in Tunis, Tunisia, by culturing on Acanthamoeba spp. and is a new marseillevirus. We describe here its 380,011 base-pair genome. A total of 484 proteins were identified, among which 320 and 358 have an ortholog in Marseillevirus and Lausannevirus (e-value<1e-2), respectively, and 259 and 299 have best reciprocal hits with a Marseillevirus and a Lausannevirus protein, respectively. In addition, a significant hit was found in organisms other than marseilleviruses for 144 Tunisvirus proteins, indicating extensive lateral gene transfers, as has been demonstrated previously for Marseillevirus. Finally, a total of 21 ORFans were identified. Phylogeny reconstructions and analysis of the gene repertoires of marseilleviruses, including the proportion of orthologs and the mean amino acid identity between genes in pairs, suggest that the proposed family Marseilleviridae encompasses three lineages. Lineage A is composed of Marseillevirus, Cannes 8 virus and Senegalvirus; lineage B is represented by Lausannevirus alone; and lineage C has Tunisvirus as its first member. Taken together, these findings suggest that the marseilleviruses display a substantial level of diversity.

Zamilon, a novel virophage with Mimiviridae host specificity.

Virophages, which are potentially important ecological regulators, have been discovered in association with members of the order Megavirales. Sputnik virophages target the Mimiviridae, Mavirus was identified with the Cafeteria roenbergensis virus, and virophage genomes reconstructed by metagenomic analyses may be associated with the Phycodnaviridae. Despite the fact that the Sputnik virophages were isolated with viruses belonging to group A of the Mimiviridae, they can grow in amoebae infected by Mimiviridae from groups A, B or C. In this study we describe Zamilon, the first virophage isolated with a member of group C of the Mimiviridae family. By co-culturing amoebae with purified Zamilon, we found that the virophage is able to multiply with members of groups B and C of the Mimiviridae family but not with viruses from group A. Zamilon has a 17,276 bp DNA genome that potentially encodes 20 genes. Most of these genes are closely related to genes from the Sputnik virophage, yet two are more related to Megavirus chiliensis genes, a group B Mimiviridae, and one to Moumouvirus monve transpoviron.

First isolation of a giant virus from wild Hirudo medicinalis leech: Mimiviridae isolation in Hirudo medicinalis.

Giant viruses and amoebae are common in freshwater, where they can coexist with other living multicellular organisms. We screened leeches from the species Hirudo medicinalis for giant viruses. We analyzed five H. medicinalis obtained from Tunisia (3) and France (2). The leeches were decontaminated and then dissected to remove internal parts for co-culture with Acanthamoeba polyphaga. The genomes of isolated viruses were sequenced on a 454 Roche instrument, and a comparative genomics analysis was performed. One Mimivirus was isolated and the strain was named Hirudovirus. The genome assembly generated two scaffolds, which were 1,155,382 and 25,660 base pairs in length. Functional annotations were identified for 47% of the genes, which corresponds to 466 proteins. The presence of Mimividae in the same ecological niche as wild Hirudo may explain the presence of the mimivirus in the digestive tract of the leech, and several studies have already shown that viruses can persist in the digestive tracts of leeches fed contaminated blood. As leeches can be used medically and Mimiviruses have the potential to be an infectious agent in humans, patients treated with leeches should be surveyed to investigate a possible connection.

A decade of improvements in Mimiviridae and Marseilleviridae isolation from amoeba.

Since the isolation of the first giant virus, the Mimivirus, by T.J. Rowbotham in a cooling tower in Bradford, UK, and after its characterisation by our group in 2003, we have continued to develop novel strategies to isolate additional strains. By first focusing on cooling towers using our original time-consuming procedure, we were able to isolate a new lineage of giant virus called Marseillevirus and a new Mimivirus strain called Mamavirus. In the following years, we have accumulated the world's largest unique collection of giant viruses by improving the use of antibiotic combinations to avoid bacterial contamination of amoeba, developing strategies of preliminary screening of samples by molecular methods, and using a high-throughput isolation method developed by our group. Based on the inoculation of nearly 7,000 samples, our collection currently contains 43 strains of Mimiviridae (14 in lineage A, 6 in lineage B, and 23 in lineage C) and 17 strains of Marseilleviridae isolated from various environments, including 3 of human origin. This study details the procedures used to build this collection and paves the way for the high-throughput isolation of new isolates to improve the record of giant virus distribution in the environment and the determination of their pangenome.

First isolation of a Marseillevirus in the Diptera Syrphidae Eristalis tenax.

OBJECTIVE: Giant viruses and amoebae are common in freshwater, where they can coexist with various insects. We screened insect larvae to detect giant viruses using a high-throughput method. METHODS: We analyzed 86 Eristalis tenax larvae obtained from stagnant water reservoirs in Tunisia. The larvae were decontaminated and then dissected to remove internal parts for coculture with Acanthamoeba polyphaga. Genome sequencing of isolated viruses was performed on a 454 Roche instrument, and comparative genomics were performed. RESULTS: One Marseillevirus, named Insectomime virus, was isolated. The genome assembly generated two scaffolds, which were 382,776 and 3,855 bp in length. Among the 477 identified predicted proteins, the best hit for 435 of the identified proteins was a Marseillevirus or Lausannevirus protein. Tunisvirus was the most closely related to Insectomime, with 446 orthologs. One Insectomime protein shared with Lausannevirus and Tunisvirus showed the highest similarity with a protein from an aphid. CONCLUSION: The isolation of a Marseillevirus from an insect expands the diversity of environments in which giant viruses have been isolated. The coexistence of larvae and giant viruses in stagnant water may explain the presence of the giant virus in the larva internal structures. This study illustrates the putative role of amoeba in lateral gene transfer not only between the organisms it phagocytoses, but also between organisms living in the same environment. © 2013 S. Karger AG, Basel.

Alcohol disinfection procedure for isolating giant viruses from contaminated samples.

OBJECTIVE: Giant viruses of the Megavirales order have been neglected in the literature because they are removed from samples during viral purification for viral metagenomic studies. Isolation via amoeba coculture has low efficiency and is extremely time-consuming. Thus, our objective was to improve Megavirales detection and recovery by using a new protocol that will eliminate most bacteria present in environmental samples while preserving giant virus viability. METHODS: In this study, we tested the ability of a number of disinfection protocols to kill contaminating bacteria. These treatments were ethanol, UV irradiation, desiccation, glutaraldehyde and thermal shock. RESULTS: Of all the treatments, a brief ethanol treatment did not significantly reduce the titer of viable viral particles of Acanthamoeba polyphaga mimivirus or Marseillevirus, whereas it efficiently killed Escherichia coli. This treatment was applied to environmental samples that previously tested positive for giant viruses and was shown to eliminate contaminating bacteria, whereas it allowed for the isolation of the giant viruses. CONCLUSION: Our results demonstrate that ethanol treatment can be used to evaluate large collections of environmental samples for the presence of giant viruses and to provide insight into understanding their ecology. This study should also facilitate the isolation of giant viruses using other species of protozoa in addition to Acanthamoeba spp.

First isolation of Mimivirus in a patient with pneumonia.

BACKGROUND: Mimiviridae Mimivirus, including the largest known viruses, multiply in amoebae. Mimiviruses have been linked to pneumonia, but they have never been isolated from patients. To further understand the pathogenic role of these viruses, we aimed to isolate them from a patient presenting with pneumonia. METHODS: We cultured, on Acanthamoeba polyphaga amoebae, pulmonary samples from 196 Tunisian patients with community-acquired pneumonia during the period 2009-2010. An improved technique was used for Mimivirus isolation, which used agar plates where the growth of giant viruses is revealed by the formation of lysis plaques. Mimivirus serology was tested by microimmunofluorescence and by bidimensional immunoproteomic analysis using Mimivirus strains, to identify specific immunoreactive proteins. The new Mimivirus strain genome sequencing was performed on Roche 454 GS FLX Titanium, then AB SOLiD instruments. RESULTS: We successfully isolated a Mimivirus (LBA111), the largest virus ever isolated in a human sample, from a 72-year-old woman presenting with pneumonia. Electron microscopy revealed a Mimivirus-like virion with a size of 554 ± 10 nm. The LBA111 genome is 1.23 megabases, and it is closely related to that of Megavirus chilensis. Furthermore, the serum from the patient reacted specifically to the virus compared to controls. CONCLUSIONS: This is the first Mimivirus isolated from a human specimen. The findings presented above together with previous works establish that mimiviruses can be associated with pneumonia. The common occurrence of these viruses in water and soil makes them probable global agents that are worthy of investigation.

High-throughput isolation of giant viruses of the Mimiviridae and Marseilleviridae families in the Tunisian environment.

Giant viruses of the Megavirales order have been recently isolated from aquatic environments and have long been neglected because they are removed from samples during viral purification for viral metagenomic studies. Due to bacterial overgrowth and susceptibility to high concentrations of antibiotics, isolation by amoeba co-culture has a low efficiency and is highly time-consuming. Thus, few environments have been exhaustively investigated to date, although the ubiquitous distribution of the Acanthamoeba sp. suggests that these viruses could also be ubiquitous. In this work, we have implemented a high-throughput method to detect amoebae lysis on agar plates that allows the testing of hundreds of samples in a few days. Using this procedure, a total of 11 new Marseilleviridae strains and four new Mimiviridae strains, including a virus infected with a virophage, were isolated from 1000 environmental samples from Tunisia. Of these, four corresponded to new genotypic variants. These isolates are the first African environmental isolates identified from these two families, and several samples were obtained from a hypersaline aquatic environment. These results demonstrate that this technique can be used for the evaluation and characterization of large collections of giant viruses to provide insight into understanding their ecology.

Genome sequence of Legionella tunisiensis strain LegM(T), a new Legionella species isolated from hypersaline lake water.

Legionella tunisiensis is a gammaproteobacterium from the class Legionellaceae, growing in amoebae. We sequenced the genome from strain LegM(T). It is composed of 3,508,121 bp and contains 4,747 protein-coding genes and 38 RNA genes, including 3 rRNA genes.

Legionella tunisiensis sp. nov. and Legionella massiliensis sp. nov., isolated from environmental water samples.

Two isolates of intra-amoeba-growing bacteria, LegA(T) ( = DSM 24804(T) = CSUR P146(T)) and LegM(T) ( = DSM 24805(T) = CSUR P145(T)), were characterized on the basis of microscopic appearance, staining characteristics, axenic growth at different temperatures and the sequences of the mip, rpoB, 16S rRNA and rnpb genes, as well as the 23S-5S region. Phylogenetic analysis showed that these two isolates lay within the radius of the family Legionellaceae. Furthermore, the analysis of these genes yielded congruent data that indicated that, although strain LegM(T) clusters specifically with Legionella feeleii ATCC 35072(T) and LegA(T) clusters with Legionella nautarum ATCC 49596(T), the divergence observed between these species was greater than that observed between other members of the family. Taken together, these results support the proposal that these two isolates represent novel members of the genus Legionella, and we propose to name them Legionella tunisiensis sp. nov. for LegM(T) ( = DSM 24805(T) = CSUR P145(T)) and Legionella massiliensis sp. nov. for LegA(T) ( = DSM 24804(T) = CSUR P146(T)).