新型淡水微囊藻噬藻体vB_MweS-yong2的分离与基因组分析

Isolation and genome analysis of a new freshwater Microcystis cyanophage vB_MweS-yong2

摘要:

【目的】蓝藻(cyanobacteria)水华频繁暴发，引起水质恶化，使水生生物大量死亡，给水产养殖业造成巨大的经济损失；其代谢产物藻毒素具有肝毒性、神经毒性、生殖毒性、遗传毒性和肿瘤促进作用，并可在水生生物中富集，造成饮用水安全风险和水产品食用安全风险。噬藻体(cyanophages)是一类特异性侵染蓝藻的病毒，参与调控蓝藻的种群密度和丰度，被认为是极具潜力的蓝藻水华生物防控工具。以往的研究报道多集中于海水噬藻体，有关淡水噬藻体的报道寥寥无几，迄今尚无惠氏微囊藻(Microcystis wesenbergii)噬藻体的研究报道。本研究的目的在于分离、鉴定惠氏微囊藻噬藻体。【方法】以惠氏微囊藻FACHB-1112为指示宿主，采用双层平板法从淡水中分离出噬藻体vB_MweS-yong2，对其进行全基因组测序、基因功能注释和系统进化分析。【结果】vB_MweS-yong2的基因组长44 530 bp，G+C含量为71.6%，有61个开放阅读框(ORF)、1个tRNA基因。成对序列比较 (pairwise sequence comparison，PASC)表明，vB_MweS-yong2与所有已知噬菌体间的全基因组核苷酸序列相似度最高只有20.21%，小于<50%的属边界值。没有在vB_MweS-yong2基因组中发现抗生素耐药基因和毒力因子基因，显示该噬藻体在基因水平上的安全性。【结论】vB_MweS-yong2在有尾目的长尾科中代表一个新的属。本研究丰富了淡水噬藻体库、基因库，并为以后研发该噬藻体的功能基因、进一步研发用于治理以惠氏微囊藻为优势种引起的水华的产品与技术奠定了基础。

Abstract:

[Objective] Cyanobacterial blooms break out frequently and cause water quality deterioration.Cyanobacterial toxins (cyanotoxins) have hepatotoxicity,neurotoxicity,reproductive and genetic toxicity and tumor promoting effects,threatening the drinking water safety.Cyanobacterial blooms contribute to toxin accumulation or death of aquatic organisms,risking edible safety of aquatic products and causing huge economic losses to aquaculture industry.Cyanophages are viruses that specifically infect cyanobacteria and regulate its population density and abundance.They are considered as an important potential biological control tool for cyanobacterial blooms.Study on freshwater cyanophage is rarely reported,which is far less than that on seawater cyanophage.So far,little is known about Microcystis wesenbergii cyanophage.[Methods] In this study,we isolated a virulent freshwater cyanophage vB_MweS-yong2 by double-layer agar plate method using M.wesenbergii FACHB-1112 as the indicator host.Genome sequencing,open reading frame (ORF) annotation and phylogenetic analysis of cyanophage vB_MweS-yong2 were performed.[Results]vB_MweS-yong2 genome was a double-stranded DNA of 44 530 bp,with a G+C content of 71.6% and containing 61 ORFs and 1 tRNA gene.No vB_MweS-yong2 ORF was found to be associated with virulence factors and antibiotic resistance genes.The pairwise sequence comparison (PASC) scanning illustrated that the highest nucleotide sequence similarity between vB_MweS-yong2 and all known phages in databases was 20.21%,which was<50%(the boundary to define a genus).[Conclusion] vB_MweS-yong2 was proposed to represent a new genus in the Siphoviridae family of Caudovirales order.These works enriched the freshwater cyanophage database and laid a foundation for the research and development of the functional genes of cyanophages and the control of cyanobacterial blooms with M.wesenbergii as the dominant species.