Goldin Svetlana, Hulata Yotam, Baran Nava, Lindell Debbie
Faculty of Biology, Technion - Israel Institute of Technology, Haifa, Israel.
Front Microbiol. 2020 Jun 16;11:1210. doi: 10.3389/fmicb.2020.01210. eCollection 2020.
The North Pacific Subtropical Gyre (NPSG) is one of the largest biomes on Earth, with the cyanobacterium being the most abundant primary producer year-round. Viruses that infect cyanobacteria (cyanophages) influence cyanobacterial mortality, diversity and evolution. Two major cyanophage families are the T4-like cyanomyoviruses and T7-like cyanopodoviruses, yet their abundances and distribution patterns remain unknown due to difficulty in quantifying their populations. To address this limitation, we previously adapted the polony method (for PCR colony) to quantify T7-like cyanophages and applied it to spring populations in the Red Sea. Here, we further adapted the method for the quantification of T4-like cyanophages and analyzed the abundances of T4-like and T7-like cyanophage populations in the photic zone of the NPSG in summer 2015 and spring 2016. Combined, the peak abundances of these two cyanophage families reached 2.8 × 10 and 1.1 × 10 cyanophages ⋅ ml in the summer and spring, respectively. They constituted between 3 and 16% of total virus-like particles (VLPs), comprising a substantial component of the virioplankton in the NPSG. While both cyanophage families were highly abundant, the T4-like cyanophages were generally 1.3-4.4 fold more so. In summer, cyanophages had similar and reproducible distribution patterns with depth. Abundances were relatively low in the upper mixed layer and increased to form a pronounced subsurface peak at 100 m (1.9 × 10 and 9.1 × 10 phages ⋅ ml for the T4-like and T7-like cyanophages, respectively), coincident with the maximum in populations. Less vertical structure in cyanophage abundances was apparent in the spring profile, despite a subsurface peak in numbers. In the summer upper mixed layer, cyanophages constituted a smaller proportion of VLPs than below it and cyanophage to cyanobacteria ratios were considerably lower (1.3-2.8) than those of VLPs to bacteria (8.1-21.2). Differences in abundances between the two families and their contribution to VLPs with depth suggest differences in cyanophage production and/or decay processes relative to other members of the virioplankton in the upper mixed layer. These findings highlight the importance of quantifying distinct populations within the virioplankton to gain accurate understanding of their distribution patterns.
北太平洋亚热带环流（NPSG）是地球上最大的生物群落之一，蓝细菌是全年最丰富的初级生产者。感染蓝细菌的病毒（蓝噬菌体）影响蓝细菌的死亡率、多样性和进化。两个主要的蓝噬菌体家族是T4样蓝藻肌病毒和T7样蓝藻足病毒，但由于难以量化其种群数量，它们的丰度和分布模式仍然未知。为了解决这一限制，我们之前采用了聚合酶克隆法（用于PCR菌落）来量化T7样蓝噬菌体，并将其应用于红海春季种群。在此，我们进一步改进了该方法以量化T4样蓝噬菌体，并分析了2015年夏季和2016年春季NPSG光合层中T4样和T7样蓝噬菌体种群的丰度。综合来看，这两个蓝噬菌体家族的峰值丰度在夏季和春季分别达到2.8×10和1.1×10蓝噬菌体·毫升。它们占病毒样颗粒（VLP）总数的3%至16%，构成了NPSG中病毒浮游生物的重要组成部分。虽然两个蓝噬菌体家族都高度丰富，但T4样蓝噬菌体通常多1.3 - 4.4倍。在夏季，蓝噬菌体在不同深度具有相似且可重复的分布模式。在上层混合层丰度相对较低，并在100米处增加形成明显的次表层峰值（T4样和T7样蓝噬菌体分别为1.9×10和9.1×10噬菌体·毫升），与种群数量最大值一致。尽管春季蓝细菌数量有次表层峰值，但蓝噬菌体丰度的垂直结构不太明显。在夏季上层混合层，蓝噬菌体占VLP的比例低于其下方，蓝噬菌体与蓝细菌的比例（1.3 - 2.8）远低于VLP与细菌的比例（8.1 - 21.2）。两个家族之间丰度的差异以及它们在不同深度对VLP的贡献表明，相对于上层混合层中病毒浮游生物的其他成员，蓝噬菌体的产生和/或衰变过程存在差异。这些发现突出了量化病毒浮游生物中不同种群以准确了解其分布模式的重要性。
