Project: Investigation of viruses and microbes circulating deep in the seafloor

NSF Award Abstract:
The ocean does not end at the seafloor. Seawater penetrates deep into the ocean crust forming an enormous subseafloor aquifer. Interactions among seawater, rocks, and microorganisms alter the properties of seawater as it passes through this aquifer. The flux of the altered fluid out of the basaltic rocks and back into the sea is equivalent to the flux of all the rivers on the planet and this exchange of deep-sea fluids influences the chemical balance of the ocean. Obtaining samples of these fluids has been a major obstacle to understanding the biological processes that occur within the ocean basement aquifer, but the development and installation of special wellheads, called CORKs, into boreholes on the seafloor now provides opportunities to probe the biology of the most remote habitat on earth. Recent analyses of fluids sampled from CORKs have shown that the microbial communities in the ocean basement are very different from those of the overlying seawater, but little is known of their ecology. In particular, nothing is known about how viruses interact with the cells in this habitat. When a lytic virus infects a cell, it will lyse and kill the cell, but temperate viruses often establish a stable, symbiotic relationship with the host cell that changes how the cell functions. Because of these important roles, viruses exert a major influence on the size, composition, and activity of microbial communities. Investigating the contributions of lytic and temperate viruses in the ocean basement is therefore central to understanding how activities of microbes in the basement are regulated. For this project, the researchers will sample fluids from the ocean basement in the central Atlantic Ocean to conduct the first investigation of the importance of viruses in a slow spreading crustal system. In addition to publishing the detailed results in scientific journals, the researchers will produce a book (in English and Hawaiian) targeting upper elementary to middle schoolchildren that captures the excitement and challenges of deep-sea exploration and introduces the mysteries of the life forms being discovered deep in the earth?s crust. The book will align with National Ocean Literacy Principles and Common Core Standards. Distribution will be focused on the minority-serving schools in Hawaii with the goal of fostering interest in the ocean, earth, and life sciences in groups traditionally underrepresented in STEM fields.

To collect the viruses and microorganisms in the fluids, the researchers will use both passive and active collection methods with the help of a remotely operated vehicle. For passive collection, micro- and ultrafilters will be connected in series to the wellhead and fluids will be driven through the filters by the pressure differential between aquifer and bottom seawater. For active sampling, mechanical pumps will be used to direct either basement fluids or bottom seawater into sample bags for retrieval and processing aboard ship. Microorganisms and viruses harvested from the fluids will be fractionated to separate populations. The viruses and cells will be examined by electron microscopy to quantify morphological diversity and to determine the proportion of infected cells. Nucleic acids from the cells and viruses will be sequenced to 1) characterize the genetic diversity of the viruses, 2) determine the proportion of cells with integrated viral genomes, 3) identify the functional genes contributed to the cells by the viruses, and 4) link specific viruses to their likely hosts based on analysis of CRISPR elements. The researchers hypothesize that the basement viruses will be distinct from those of bottom seawater and that, compared to surface seawater where cells are more abundant, active lytic infections in the basement will be low, but infections by temperate viruses will be exceptionally common. The data from this project will help to constrain the importance of viruses in recycling of organic carbon in the ocean basement and shed light on how viral genes may be altering the microbial activities that influence ocean chemistry.