北京时间10月16日消息，在智利海域，科学家发现了世界上个头最大的病毒，拥有1000多个基因。这一发现让科学家陷入惊讶之中。这种病毒被称之为“Megavirus chilensis”，基因组含有近126万个碱基对，是最为复杂的DNA病毒，个头比此前的纪录保持者――2003年分离出的拟菌病毒大6.5%。
这种巨型病毒是在智利拉斯克鲁塞斯一个研究站附近提取的海水样本中发现的。病毒与细菌不同，它们的个头往往更小，同时无法自行繁殖，需要进入宿主细胞内进行繁殖。拟菌病毒等病毒能够感染棘骨变形虫等单细胞生物，但研究人员并不确定M. chilensis是否也是这种情况。
虽然可以利用普通显微镜进行观察，但法国艾克斯-马赛大学的让-米切尔-克拉维莱教授和同事还是使用电子显微镜对这种病毒进行拍摄和测量。根据他们的测量结果，足球形的M. chilensis病毒直径680纳米，个头超过绝大多数细菌。其表面覆盖一层纤维，其中一两个区域的厚度更大，好似一绺绺头发。
目前，研究人员还不清楚这种病毒为何拥有如此大的个头。一种假设认为，随着时间的流逝，M. chilensis病毒不断“偷盗”前宿主的DNA，这一过程被称之为“基因转移”。另一种观点认为，M. chilensis病毒和拟菌病毒源自一个更为复杂的祖先，继承了祖先的细胞基因组。克拉维莱教授表示，DNA病毒包括痘病毒和疱疹病毒，M. chilensis似乎对人体无害。在本周出版的美国《国家科学院院刊》上，研究人员对这种病毒进行了描述。（生物谷 Bioon.com）
doi:10.1073/pnas.1110889108
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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).
