Ocean viruses and their effects on microbial communities and biogeochemical cycles

Abstract

Viruses are the most abundant life forms on Earth, with an estimated 10(31) total viruses globally. The majority of these viruses infect microbes, whether bacteria, archaea or microeukaryotes. Given the importance of microbes in driving global biogeochemical cycles, it would seem, based on numerical abundances alone, that viruses also play an important role in the global cycling of carbon and nutrients. However, the importance of viruses in controlling host populations and ecosystem functions, such as the regeneration, storage and export of carbon and other nutrients, remains unresolved. Here, we report on advances in the study of ecological effects of viruses of microbes. In doing so, we focus on an area of increasing importance: the role that ocean viruses play in shaping microbial population sizes as well as in regenerating carbon and other nutrients.

Figure 1.. Schematic of the viral shunt

The lysis of microbes by viruses releases cellular material into the environment. Some of this cellular material can be utilized by microbes for subsequent metabolic processes. Here, we note that available dissolved organic material (DOM) and particulate organic material (POM) is utilized primarily by heterotrophs (the thicker arrow leading downward from the DOM/POM pool). Note that many other processes are not included in this schematic, e.g. sinking out of the system, exudation during growth, light input, or the influx of inorganic carbon and nutrients. Abbreviations: DOM, dissolved organic material; POM, particulate organic material.

Figure 2.. Schematic of the role of viruses in the differential regeneration of organic matter

The release of cellular materials by viral lysis depicted in Figure 1 increases the dissolved organic matter (DOM) and particulate organic matter (POM) in the environment. Lysis also changes the abundance of distinct biomolecules. Here, for purposes of illustration, we simplify the high-dimensional configuration space of biomolecules into a one-dimensional axis. The x-axis denotes the degree to which organic material is easy to utilize by organisms (i.e. labile) vs. hard to utilize by organisms (i.e. recalcitrant). The y-axis denotes the amount of organic material across this accessibility spectrum. The vertical arrows denote how a particular process can change the availability of different organic materials, potentially in non-uniform ways. The horizontal arrows denote that some processes may convert material from one state to another without changing the total amount of material. The size of the arrows represents an estimated magnitude of a given process. We note that characterizing the space of biomolecules and the role of viruses in modifying the relative abundance of biomolecules is an ongoing challenge. There are data to substantiate the existence of horizontal and vertical arrows (e.g. [41]) but less data to substantiate the correct size of horizontal and vertical arrows. Abbreviations: DOM, dissolved organic material; POM, particulate organic material.