近日,，國際著名雜志Journal of Virology在線提前發(fā)表了中國科學院水生生物研究所研究人員的最新研究成果“A Novel Cyanophage with a Cyanobacterial Nonbleaching Protein A Gene in the Genome,。”，文章中,，研究人員發(fā)現(xiàn)了首株無尾噬藻體的全基因組結(jié)構(gòu)及其具有的編碼藻膽體降解蛋白的生物學功能,。
噬藻體是侵染藍藻的病毒。噬藻體與宿主的相互作用以及對藍藻高度專一的致死性感染,，可調(diào)節(jié)控制水華藍藻的密度與種群結(jié)構(gòu),，減少藍藻水華的形成與危害，有助于藍藻細胞溶解物參與地球生物化學循環(huán)。作為一種潛在控制有害藍藻水華的生物效應(yīng)因子,，噬藻體成為水生病毒學和水環(huán)境科學研究的熱點對象,。
近日，中國科學院水生生物研究所張奇亞團隊和桂建芳團隊共同闡明了首株無尾噬藻體PaV-LD(Planktothrix agardhii Virus from Lake Dong -hu) 全基因組結(jié)構(gòu)及其編碼的藻膽體降解蛋白(NblA)的生物學功能,。PaV-LD是從武漢東湖水樣中培養(yǎng)分離的水華絲狀藍藻噬藻體,，其基因組為雙鏈DNA,，共有95299個堿基對,，含有142個推導基因。質(zhì)譜分析從PaV-LD中鑒定出13個分子量大小范圍在 27KDa 至 172KDa 的主要結(jié)構(gòu)蛋白,，但缺少已知噬藻(菌)體必備的幾種尾結(jié)構(gòu)蛋白,。系統(tǒng)進化分析揭示，PaV-LD主要衣殼蛋白結(jié)構(gòu)與已知有尾噬藻(菌)體也大不相同,，為一個新的獨立分枝,；與有尾噬藻體比較，電鏡觀察也確信PaV-LD為無尾噬藻體,。重要的是,，PaV-LD基因組中的ORF 022L基因是一個藍藻NblA同源基因，而該基因通常只存在于藍藻細胞中,，是藻膽體蛋白降解的關(guān)鍵基因,。通過基因克隆、免疫印跡,、光譜測定和電鏡觀察等綜合分析,，證實了PaV-LD的ORF 022L確實能編碼具有藍藻NblA功能的蛋白。PaV-LD ORF 022L表達,，能使藍藻培養(yǎng)物由藍綠色變成淺黃色,，細胞中藻膽體蛋白含量顯著下降，藻的類囊體結(jié)構(gòu)遭受破壞或完全消失,。
這一新型無尾噬藻體全基因組的解析及其存在的藻膽體降解蛋白基因生物學功能的詮釋,，為了解噬藻體的遺傳多樣性、噬藻體與宿主和環(huán)境的相互作用,，以及噬藻體功能基因的控藻機理等研究新開啟了一扇門,。該研究得到中科院知識創(chuàng)新工程 (KSCX2-EW-Z-3)、國家973(2010CB126303, 2009CB118704)和國家自然科學基金(30871938, 31072239)等項目的資助,。（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.
