Laboratory of Microbiology of Extreme Environments, lnstitut Universitaire Européen de la Mer, Plouzané, 29280, France.
LabMCT, Belgian Department of Defense, Queen Astrid Military Hospital, Brussels, 1120, Belgium.
Biol Rev Camb Philos Soc. 2017 May;92(2):1081-1100. doi: 10.1111/brv.12271. Epub 2016 Apr 26.
The discovery of the numerical importance of viruses in a variety of (aquatic) ecosystems has changed our perception of their importance in microbial processes. Bacteria and Archaea undoubtedly represent the most abundant cellular life forms on Earth and past estimates of viral numbers (represented mainly by viruses infecting prokaryotes) have indicated abundances at least one order of magnitude higher than that of their cellular hosts. Such dominance has been reflected most often by the virus-to-prokaryote ratio (VPR), proposed as a proxy for the relationship between viral and prokaryotic communities. VPR values have been discussed in the literature to express viral numerical dominance (or absence of it) over their cellular hosts, but the ecological meaning and interpretation of this ratio has remained somewhat nebulous or contradictory. We gathered data from 210 publications (and additional unpublished data) on viral ecology with the aim of exploring VPR. The results are presented in three parts: the first consists of an overview of the minimal, maximal and calculated average VPR values in an extensive variety of different environments. Results indicate that VPR values fluctuate over six orders of magnitude, with variations observed within each ecosystem. The second part investigates the relationship between VPR and other indices, in order to assess whether VPR can provide insights into virus-host relationships. A positive relationship was found between VPR and viral abundance (VA), frequency of visibly infected cells (FVIC), burst size (BS), frequency of lysogenic cells (FLC) and chlorophyll a (Chl a) concentration. An inverse relationship was detected between VPR and prokaryotic abundance (PA) (in sediments), prokaryotic production (PP) and virus-host contact rates (VCR) as well as salinity and temperature. No significant relationship was found between VPR and viral production (VP), fraction of mortality from viral lysis (FMVL), viral decay rate (VDR), viral turnover (VT) or depth. Finally, we summarize our results by proposing two scenarios in two contrasting environments, based on current theories on viral ecology as well as the present results. We conclude that since VPR fluctuates in every habitat for different reasons, as it is linked to a multitude of factors related to virus-host dynamics, extreme caution should be used when inferring relationships between viruses and their hosts. Furthermore, we posit that the VPR is only useful in specific, controlled conditions, e.g. for the monitoring of fluctuations in viral and host abundance over time.
病毒在各种（水生）生态系统中的数量重要性的发现改变了我们对其在微生物过程中的重要性的认识。细菌和古菌无疑代表了地球上最丰富的细胞生命形式，过去对病毒数量的估计（主要代表感染原核生物的病毒）表明，其丰度至少比其细胞宿主高一个数量级。这种优势最常通过病毒-原核生物比（VPR）来反映，该比被提议作为病毒和原核生物群落之间关系的替代指标。VPR 值在文献中被讨论以表达病毒对其细胞宿主的数量优势（或不存在优势），但该比率的生态意义和解释仍然有些模糊或矛盾。我们从 210 篇关于病毒生态学的出版物（和额外的未发表数据）中收集了数据，目的是探索 VPR。结果分为三部分：第一部分概述了广泛不同环境中最小、最大和计算的平均 VPR 值。结果表明，VPR 值在六个数量级上波动，每个生态系统内都有变化。第二部分研究了 VPR 与其他指标之间的关系，以评估 VPR 是否可以提供有关病毒-宿主关系的见解。发现 VPR 与病毒丰度（VA）、可见感染细胞的频率（FVIC）、爆发大小（BS）、溶原细胞的频率（FLC）和叶绿素 a（Chl a）浓度呈正相关。VPR 与原核生物丰度（PA）（在沉积物中）、原核生物生产力（PP）和病毒-宿主接触率（VCR）以及盐度和温度呈负相关。VPR 与病毒生产力（VP）、病毒裂解死亡率（FMVL）、病毒衰减率（VDR）、病毒周转率（VT）或深度之间没有显著关系。最后，我们根据当前的病毒生态学理论以及当前的结果，在两个对比的环境中提出了两种情景来总结我们的结果。我们得出的结论是，由于 VPR 在每个栖息地中都因不同的原因而波动，因为它与与病毒-宿主动态相关的多种因素有关，因此在推断病毒与其宿主之间的关系时应格外小心。此外，我们认为 VPR 仅在特定的、受控的条件下有用，例如用于监测病毒和宿主丰度随时间的波动。
