北京時間10月16日消息,，在智利海域，科學家發(fā)現(xiàn)了世界上個頭最大的病毒,，擁有1000多個基因,。這一發(fā)現(xiàn)讓科學家陷入驚訝之中。這種病毒被稱之為“Megavirus chilensis”,，基因組含有近126萬個堿基對,，是最為復雜的DNA病毒，個頭比此前的紀錄保持者――2003年分離出的擬菌病毒大6.5%,。
這種巨型病毒是在智利拉斯克魯塞斯一個研究站附近提取的海水樣本中發(fā)現(xiàn)的,。病毒與細菌不同，它們的個頭往往更小,，同時無法自行繁殖,，需要進入宿主細胞內(nèi)進行繁殖。擬菌病毒等病毒能夠感染棘骨變形蟲等單細胞生物,，但研究人員并不確定M. chilensis是否也是這種情況,。
雖然可以利用普通顯微鏡進行觀察，但法國艾克斯-馬賽大學的讓-米切爾-克拉維萊教授和同事還是使用電子顯微鏡對這種病毒進行拍攝和測量,。根據(jù)他們的測量結(jié)果,，足球形的M. chilensis病毒直徑680納米，個頭超過絕大多數(shù)細菌,。其表面覆蓋一層纖維,，其中一兩個區(qū)域的厚度更大，好似一綹綹頭發(fā),。
目前,，研究人員還不清楚這種病毒為何擁有如此大的個頭。一種假設認為,，隨著時間的流逝,，M. chilensis病毒不斷“偷盜”前宿主的DNA，這一過程被稱之為“基因轉(zhuǎn)移”,。另一種觀點認為,，M. chilensis病毒和擬菌病毒源自一個更為復雜的祖先，繼承了祖先的細胞基因組,?？死S萊教授表示，DNA病毒包括痘病毒和皰疹病毒,，M. chilensis似乎對人體無害,。在本周出版的美國《國家科學院院刊》上，研究人員對這種病毒進行了描述。（生物谷 Bioon.com）
doi:10.1073/pnas.1110889108
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PMID:
Distant Mimivirus relative with a larger genome highlights the fundamental features of Megaviridae
Arslan, Defne; Legendre, Matthieu; Seltzer, Virginie; Abergel, Chantal; Claverie, Jean-Michel
Mimivirus, a DNA virus infecting acanthamoeba, was for a long time the largest known virus both in terms of particle size and gene content. Its genome encodes 979 proteins, including the first four aminoacyl tRNA synthetases (ArgRS, CysRS, MetRS, and TyrRS) ever found outside of cellular organisms. The discovery that Mimivirus encoded trademark cellular functions prompted a wealth of theoretical studies revisiting the concept of virus and associated large DNA viruses with the emergence of early eukaryotes. However, the evolutionary significance of these unique features remained impossible to assess in absence of a Mimivirus relative exhibiting a suitable evolutionary divergence. Here, we present Megavirus chilensis, a giant virus isolated off the coast of Chile, but capable of replicating in fresh water acanthamoeba. Its 1,259,197-bp genome is the largest viral genome fully sequenced so far. It encodes 1,120 putative proteins, of which 258 (23%) have no Mimivirus homologs. The 594 Megavirus/Mimivirus orthologs share an average of 50% of identical residues. Despite this divergence, Megavirus retained all of the genomic features characteristic of Mimivirus, including its cellular-like genes. Moreover, Megavirus exhibits three additional aminoacyl-tRNA synthetase genes (IleRS, TrpRS, and AsnRS) adding strong support to the previous suggestion that the Mimivirus/Megavirus lineage evolved from an ancestral cellular genome by reductive evolution. The main differences in gene content between Mimivirus and Megavirus genomes are due to (i) lineages specific gains or losses of genes, (ii) lineage specific gene family expansion or deletion, and (iii) the insertion/migration of mobile elements (intron, intein).
