Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
Appl Environ Microbiol. 2019 Aug 29;85(18). doi: 10.1128/AEM.01170-19. Print 2019 Sep 15.
Viruses play important roles in regulating the abundance and composition of bacterial populations in aquatic ecosystems. The bloom-forming toxic cyanobacterium is predicted to interact with diverse cyanoviruses, resulting in population diversification. However, current knowledge of the genomes from these viruses and their infection programs is limited to those of virus Ma-LMM01. Here, we performed a time series sampling at a small pond in Japan during a bloom and then investigated the genomic information and transcriptional dynamics of -interacting viruses using metagenomic and metatranscriptomic approaches. We identified 15 viral genomic fragments classified into three groups, groups I (including Ma-LMM01), II (high abundance and transcriptional activity), and III (new lineages). According to the phylogenetic distribution of strains possessing spacers against each viral group, the group II-original viruses interacted with all three phylogenetically distinct population types (phylotypes), whereas the groups I and III-original viruses interacted with only one or two phylotypes, indicating the cooccurrence of broad- (group II) and narrow (groups I and III)-host-range viruses in the bloom. These viral fragments showed the highest transcriptional levels during daytime regardless of their genomic differences. Interestingly, expressed antiviral defense genes in the environment, unlike what was seen with an Ma-LMM01 infection in a previous culture experiment. Given that broad-host-range viruses often induce antiviral responses within alternative hosts, our findings suggest that such antiviral responses might inhibit viral multiplication, mainly that of broad-host-range viruses like those in group II. The bloom-forming toxic cyanobacterium is thought to have diversified its population through the interactions between host and viruses in antiviral defense systems. However, current knowledge of viral genomes and infection programs is limited to those of virus Ma-LMM01, which was a narrow host range in which it can escape from the highly abundant host defense systems. Our metagenomic approaches unveiled the cooccurrence of narrow- and broad-host-range viruses, which included fifteen viral genomic fragments from blooms that were classified into three groups. Interestingly, antiviral defense genes were expressed against viral infection in the environment, unlike what was seen in a culture experiment with Ma-LMM01. Given that viruses with a broad host range often induce antiviral responses within alternative hosts, our findings suggest that antiviral responses inhibit viral reproduction, especially that of broad-range viruses like those in group II. This paper augments our understanding of the interactions between and its viruses and fills an important knowledge gap.
病毒在调节水生生态系统中细菌种群的丰度和组成方面发挥着重要作用。预计形成水华的有毒蓝藻与多种噬藻体相互作用，导致种群多样化。然而，目前对这些病毒及其感染程序的基因组的了解仅限于病毒 Ma-LMM01。在这里，我们在日本的一个小池塘中进行了一系列时间序列采样，在水华期间，然后使用宏基因组和宏转录组方法研究了与 -相互作用的病毒的基因组信息和转录动态。我们鉴定了 15 个病毒基因组片段，分为三组，组 I（包括 Ma-LMM01）、组 II（高丰度和转录活性）和组 III（新谱系）。根据具有针对每个病毒组间隔子的菌株的系统发育分布，组 II-原始病毒与所有三种系统发育上不同的 -种群类型（基因型）相互作用，而组 I 和组 III-原始病毒仅与一个或两个基因型相互作用，表明在水华期间存在广泛（组 II）和狭窄（组 I 和 III）宿主范围病毒的共存。这些病毒片段无论其基因组差异如何，在白天表现出最高的转录水平。有趣的是，在环境中表达抗病毒防御基因，与之前的培养实验中观察到的 Ma-LMM01 感染不同。鉴于广泛宿主范围的病毒通常会在替代宿主中诱导抗病毒反应，我们的研究结果表明，这种抗病毒反应可能会抑制病毒的复制，主要是抑制像组 II 中的那些广泛宿主范围的病毒。形成水华的有毒蓝藻通过宿主与病毒在抗病毒防御系统中的相互作用，使其种群多样化。然而，目前对病毒基因组和感染程序的了解仅限于病毒 Ma-LMM01，它是一种窄宿主范围的病毒，可以逃避高度丰富的宿主防御系统。我们的宏基因组方法揭示了窄宿主范围和广宿主范围的病毒共存，包括从水华分离的 15 个病毒基因组片段，分为三组。有趣的是，在环境中针对病毒感染表达了抗病毒防御基因，与 Ma-LMM01 的培养实验不同。鉴于广泛宿主范围的病毒通常会在替代宿主中诱导抗病毒反应，我们的研究结果表明，抗病毒反应抑制病毒的繁殖，特别是像组 II 中的那些广泛范围的病毒。本文增加了我们对蓝藻与其病毒相互作用的理解，并填补了一个重要的知识空白。
