Re-examination of the relationship between marine virus and microbial cell abundances

Abstract

Marine viruses are critical drivers of ocean biogeochemistry and their abundances vary spatiotemporally in the global oceans, with upper estimates exceeding 10 8 per ml. Over many years, a consensus has emerged that virus abundances are typically 10-fold higher than prokaryote abundances. The use of a fixed-ratio suggests that the relationship between virus and prokaryote abundances is both predictable and linear. However, the true explanatory power of a linear relationship and its robustness across diverse ocean environments is unclear. Here, we compile 5671 prokaryote and virus abundance estimates from 25 distinct marine surveys to characterize the relationship between virus and prokaryote abundances. We find that the median virus-to-prokaryote ratio (VPR) is 10:1 and 16:1 in the near-and sub-surface oceans, respectively. Nonetheless, we observe substantial variation in the VPR and find either no or limited explanatory power using fixed-ratio models. Instead, virus abundances are better described as nonlinear, power-law functions of prokaryote abundances -particularly when considering relationships within distinct marine surveys. Estimated power-laws have scaling exponents that are typically less than 1, signifying that the VPR decreases with prokaryote density, rather than remaining fixed. The emergence of power-law scaling presents a challenge for mechanistic models seeking to understand the ecological causes and consequences of marine virusmicrobe interactions. Such power-law scaling also implies that efforts to average viral effects on microbial mortality and biogeochemical cycles using "representative" abundances or abundanceratios need to be refined if they are to be utilized to make quantitative predictions at regional or global ocean scales.

Viral dynamics in two trophically different areas in the Central Adriatic Sea

“…However, new findings suggest that lysogeny could also be favoured in environments with increased host density [18,19].…”

Virus taxonomy in the age of metagenomics

“…Although virologists have traditionally focused on viruses that cause disease in humans, domestic animals and crops, the recent advances in metagenomic sequencing, in particular high-throughput sequencing of environmental samples, have revealed a staggeringly large virome everywhere in the biosphere. At least 10 31 virus particles exist globally at any given time in most environments, including marine and freshwater habitats and metazoan gastrointestinal tracts, in which the number of detectable virus particles exceeds the number of cells by 10-100-fold [1][2][3][4][5] . To help conceptualize the sheer number of viruses in existence, their current biomass has been estimated to equal that of 75 million blue whales (approximately 200 million tonnes) and, if placed end to end, the collective length of their virions would span 65 galaxies 6 .…”

Population cycles and species diversity in dynamic Kill-the-Winner model of microbial ecosystems

“…For example, in the lab experiments 11 E. coli population suffered a dramatic collapse by a factor ~10 4 -10 5 caused by a T7 phage infection. Collapse-driven dynamics is common in both natural 12 and man-made 13-16 ecosystems in which bacteria are engaged in the continuous arms race with phages [17][18][19][20][21] . Here we propose and explore a particularly simplified dynamical interpretation of Kill-the Winner principle, in which bacterial populations are characterized by periods of competitive exponential growth punctuated by rapid and severe collapses.…”

“…For example, in the lab experiments 11 E. coli population suffered a dramatic collapse by a factor ~10 4 -10 5 caused by a T7 phage infection. Collapse-driven dynamics is common in both natural 12 and man-made [13][14][15][16] ecosystems in which bacteria are engaged in the continuous arms race with phages [17][18][19][20][21] .…”