The Deep Viriosphere: Assessing the Viral Impact on Microbial Community Dynamics in the Deep Subsurface

All regions of Earth’s biosphere that we have studied—the waters of Earth’s oceans, the soil beneath our feet, and even the air we breathe—teem with viruses. Viral particles are among the smallest biological entities on the planet, with the average viral particle measuring about 100 nm in length: a size so small that five thousand viruses, lined end to end, would fit across the thickness of a human fingernail. What they lack in size, though, they compensate with sheer abundance. If we were to line up all the viruses in the ocean, they would stretch across the diameter of the Milky Way galaxy one hundred times (Suttle 2007). Those viruses are responsible for up to 1023 infections per second in the oceans (Suttle 2007). With each new infection, viruses can have a profound impact on their hosts: they can alter the structure of a microbial population, break up cellular biomass into its constituent organic matter, or introduce new genes into their hosts. Through this activity, viruses play a role in top-down as well as bottom-up processes, and can potentially alter the course of evolution.