蓝细菌病毒A-4L在鱼腥藻(Anabaena variabilis)藻苔中形成同心圆噬斑的成因

Main reason for concentric rings plaque formation of virus infecting cyanobacteria (A-4L) in lawns of Anabaena variabilis

摘要:

摘要:【目的】分析蓝细菌病毒A-4L在鱼腥藻(Anabaena sp.) PCC 7120藻苔中形成同心圆噬斑的原因，阐明A-4L的一个重要生物学特征，为分离、鉴定和筛选新的水华蓝藻病毒提供借鉴。【方法】用初始滴度为2.8×1010PFU/mL的A-4L悬液感染鱼腥藻，在不同时间点收集裂解液绘制一步生长曲线，获得A-4L对鱼腥藻的潜伏期和释放量。将适量A-4L悬液感染不同培养时间的藻苔，逐日观察和记录藻苔病变情况。培养藻苔并接种适量A-4L悬液，分别置于完全持续光照(Light:Dark=24 h:0 h，L:D=24 h:0 h)条件;完全周期光照(L:D=14 h:10h)条件;或前3 d周期光照转后3 d持续光照的条件下，比较不同光照条件对同心圆噬斑形成的影响。然后挑取单个噬斑进行扩大培养，纯化后，负染电镜观察A-4L的超微形态。【结果】A-4L的潜伏期为0.5－2h，释放量约为247 IU/cell (Infectious Units)。在周期光照条件下，藻苔接种A-4L 3－4 d后，出现同心圆噬斑，且同心圆数量与攻毒后的天数(n)有相关性，为“n－1”;同心圆间距约为3 mm。与周期光照条件相比，在持续光照条件下未形成同心圆噬斑。而在周期光照条件转持续光照条件下，由先周期光照时所形成的同心圆在转持续光照后逐渐消失，证实同心圆噬斑的形成依赖于周期光照。负染电镜观察显示A-4L具有一个近似球形的头部，直径约为50 nm以及长度约为10 nm的尾部，形态与短尾蓝细菌病毒相似。【结论】A-4L是一株能形成同心圆噬斑的蓝细菌病毒，并揭示其同心圆噬斑形成的关键条件是周期光照。

Abstract:

Abstract:［Objective］To clarify an important biological characteristic of virus infecting cyanobacteria (A-4L) and to isolate，identify new bloom-forming cyanobacteria viruses，we studied A-4L concentric rings plaque formation in Anabaena sp．PCC7120.［Methods］One step growth curve was designed to estimate the latent period and burst size of A-4L. The initial titer of A-4L was about 2.8×1010 PFU/mL. The appropriate titer suspension of A-4L was inoculated onto the lawns of Anabaena sp．PCC 7120 which have been cultivated at different time．Pathological change of lawns was observed and recorded daily．To investigate the effect of lighting on the concentric rings plaque formation，plates were cultivated and infected under continuous lighting (L:D=24 h:0 h)，periodic lighting (L:D=14 h:10 h) or 3 days continuous lighting after periodic lighting for 3 days．The ultra-morphology of purified A-4L was observed by negative staining electron microscopy．［Results］The latent period of A-4(L) was 0.5 h － 2 h and the burst size was about 247 infectious units per cell. Under periodic lighting，concentric rings plaques were observed in the plate after infection 3 days to 4 days and the distance between two rings was about 3 mm．Statistic analysis showed that there was a correlation between the number of concentric rings in plaques and infection days，which was“n－1”．Compared with the periodic lighting，the plaques without concentric rings were observed under continuous lighting． However，the concentric rings formed under periodic lighting disappeared gradually after turning to continuous lighting，which demonstrated that the formation of concentric rings plaques depended on the periodic lighting．Negative staining electron microscopy showed that the A-4L particle had a spheroidal head with diameter about 50 nm and a tail with length about 10 nm which was similar to the characteristic morphology of cyanobacterial podoviruses．［Conclusion］ A-4L is a virus infecting cyanobacteria which can form concentric rings plaque． And periodic lighting is the key conditions for the concentric rings plaque formation of A-4L.