一项研究说，科学家发现了一种感染鞭毛虫 Cafeteria roenbergensis 的巨大海洋病毒。Cafeteria roenbergensis 是一种广泛分布的浮游生物捕食者，在海洋食物网中占据着一个关键的位置。
自从发现多噬棘阿米巴模仿病毒（Acanthamoeba polyphaga mimivirus）以来，所谓的巨病毒一直让进化生物学家感到迷惑。多噬棘阿米巴模仿病毒感染淡水阿米巴，拥有120万个碱基对的基因组，比一些细胞生物的基因组还大。
Curtis A. Suttle及其同事分析了一种感染 Cafeteria roenbergensis 的未知病毒，它在90年代早期它在德克萨斯的沿海水中曾被分离出来。这组作者说，这种病原体的基因组含有大约73万个碱基对，这可能让它成为已知最大的海洋病毒。这种被命名为 CroV 的病毒拥有大量基因，这些基因通常被活细胞用于修复它们的DNA损伤以及合成蛋白质和糖。CroV 还拥有编码病毒复制需要但是必须从宿主生物那里获取的一些蛋白质的基因。由于病毒无法独立复制，它们被归类为“非生命”。但是像 CroV 这样的拥有复制机能的功能组件的巨病毒挑战了这一分类。这组作者报告说，CroV 可能还代表了一大组大多未知但是具有生态重要性的海洋巨病毒。
英文摘要：
PNAS doi: 10.1073/pnas.1007615107
Giant virus with a remarkable complement of genes infects marine zooplankton
Matthias G. Fischera, Michael J. Allenb, William H. Wilsonc, and Curtis A. Suttlea,d,e,1
Departments of aMicrobiology and Immunology,
dBotany, and
eEarth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada V6T 1Z4;
bPlymouth Marine Laboratory, Plymouth PL1 3DH, United Kingdom; and
cBigelow Laboratory for Ocean Sciences, West Boothbay Harbor, ME 04575-0475
As major consumers of heterotrophic bacteria and phytoplankton, microzooplankton are a critical link in aquatic foodwebs. Here, we show that a major marine microflagellate grazer is infected by a giant virus, Cafeteria roenbergensis virus (CroV), which has the largest genome of any described marine virus (≈730 kb of double-stranded DNA). The central 618-kb coding part of this AT-rich genome contains 544 predicted protein-coding genes; putative early and late promoter motifs have been detected and assigned to 191 and 72 of them, respectively, and at least 274 genes were expressed during infection. The diverse coding potential of CroV includes predicted translation factors, DNA repair enzymes such as DNA mismatch repair protein MutS and two photolyases, multiple ubiquitin pathway components, four intein elements, and 22 tRNAs. Many genes including isoleucyl-tRNA synthetase, eIF-2γ, and an Elp3-like histone acetyltransferase are usually not found in viruses. We also discovered a 38-kb genomic region of putative bacterial origin, which encodes several predicted carbohydrate metabolizing enzymes, including an entire pathway for the biosynthesis of 3-deoxy-d-manno-octulosonate, a key component of the outer membrane in Gram-negative bacteria. Phylogenetic analysis indicates that CroV is a nucleocytoplasmic large DNA virus, with Acanthamoeba polyphaga mimivirus as its closest relative, although less than one-third of the genes of CroV have homologs in Mimivirus. CroV is a highly complex marine virus and the only virus studied in genetic detail that infects one of the major groups of predators in the oceans.
