近日，国际著名杂志Journal of Virology在线提前发表了中国科学院水生生物研究所研究人员的最新研究成果“A Novel Cyanophage with a Cyanobacterial Nonbleaching Protein A Gene in the Genome。”，文章中，研究人员发现了首株无尾噬藻体的全基因组结构及其具有的编码藻胆体降解蛋白的生物学功能。
噬藻体是侵染蓝藻的病毒。噬藻体与宿主的相互作用以及对蓝藻高度专一的致死性感染，可调节控制水华蓝藻的密度与种群结构，减少蓝藻水华的形成与危害，有助于蓝藻细胞溶解物参与地球生物化学循环。作为一种潜在控制有害蓝藻水华的生物效应因子，噬藻体成为水生病毒学和水环境科学研究的热点对象。
近日，中国科学院水生生物研究所张奇亚团队和桂建芳团队共同阐明了首株无尾噬藻体PaV-LD(Planktothrix agardhii Virus from Lake Dong -hu) 全基因组结构及其编码的藻胆体降解蛋白(NblA)的生物学功能。PaV-LD是从武汉东湖水样中培养分离的水华丝状蓝藻噬藻体，其基因组为双链DNA，共有95299个碱基对，含有142个推导基因。质谱分析从PaV-LD中鉴定出13个分子量大小范围在 27KDa 至 172KDa 的主要结构蛋白，但缺少已知噬藻(菌)体必备的几种尾结构蛋白。系统进化分析揭示，PaV-LD主要衣壳蛋白结构与已知有尾噬藻(菌)体也大不相同，为一个新的独立分枝；与有尾噬藻体比较，电镜观察也确信PaV-LD为无尾噬藻体。重要的是，PaV-LD基因组中的ORF 022L基因是一个蓝藻NblA同源基因，而该基因通常只存在于蓝藻细胞中，是藻胆体蛋白降解的关键基因。通过基因克隆、免疫印迹、光谱测定和电镜观察等综合分析，证实了PaV-LD的ORF 022L确实能编码具有蓝藻NblA功能的蛋白。PaV-LD ORF 022L表达，能使蓝藻培养物由蓝绿色变成浅黄色，细胞中藻胆体蛋白含量显著下降，藻的类囊体结构遭受破坏或完全消失。
这一新型无尾噬藻体全基因组的解析及其存在的藻胆体降解蛋白基因生物学功能的诠释，为了解噬藻体的遗传多样性、噬藻体与宿主和环境的相互作用，以及噬藻体功能基因的控藻机理等研究新开启了一扇门。该研究得到中科院知识创新工程 (KSCX2-EW-Z-3)、国家973(2010CB126303, 2009CB118704)和国家自然科学基金(30871938, 31072239)等项目的资助。（生物谷Bioon.com）
doi: 10.1128/JVI.06282-11
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A Novel Cyanophage with a Cyanobacterial Nonbleaching Protein A Gene in the Genome
E-Bin Gao, Jian-Fang Gui and Qi-Ya Zhang
A cyanophage, PaV-LD, has been isolated from harmful filamentous cyanobacterium Planktothrix agardhii in Lake Donghu, a shallow freshwater lake in China. Here, we present the cyanophage's genomic organization and major structural proteins. The genome is a 95,299-bp-long, linear double-stranded DNA and contains 142 potential genes. BLAST searches revealed 29 proteins of known function in cyanophages, cyanobacteria, or bacteria. Thirteen major structural proteins ranging in size from 27 kDa to 172 kDa were identified by SDS-PAGE and mass-spectrometric analysis. The genome lacks major genes that are necessary to the tail structure, and the tailless PaV-LD has been confirmed by an electron microscopy comparison with other tail cyanophages and phages. Phylogenetic analysis of the major capsid proteins also reveals an independent branch of PaV-LD that is quite different from other known tail cyanophages and phages. Moreover, the unique genome carries a nonbleaching protein A (NblA) gene (open reading frame [ORF] 022L), which is present in all phycobilisome-containing organisms and mediates phycobilisome degradation. Western blot detection confirmed that 022L was expressed after PaV-LD infection in the host filamentous cyanobacterium. In addition, its appearance was companied by a significant decline of phycocyanobilin content and a color change of the cyanobacterial cells from blue-green to yellow-green. The biological function of PaV-LD nblA was further confirmed by expression in a model cyanobacterium via an integration platform, by spectroscopic analysis and electron microscopy observation. The data indicate that PaV-LD is an exceptional cyanophage of filamentous cyanobacteria, and this novel cyanophage will also provide us with a new vision of the cyanophage-host interactions.
