Award: OCE-1233306

The focus of this project was on discovering what kinds of microbes live on rocks below the seafloor, and what impact that they might have on the cycling of chemicals in the ocean, which may ultimately impact life elsewhere in the ocean. Rocks below the seafloor make up the largest potential habitat for life on Earth, yet we know very little about what life in this environment is like. This project specifically focused on rocks that were collected during an international scientific ocean drilling expedition to the western side of the Mid-Atlantic Ridge (Integrated Ocean Drilling Program Expedition 336), where rocks are made of basalt and exposed to cool fluids that circulate through the seafloor, but other samples-of-opportunity from other deep-sea environments were also included for comparison. Results of this project documented, for the first time, the potential for microbes in this environment to respire ("breathe") oxygen, and set a boundary on what the rates of oxygen consumption in this environment might be. This value is important because it helps us to understand how microbes might be involved in "weathering" the rocks below the seafloor. We also documented, for the first time, the potential rates at which microbes growing on basalts can convert carbon dioxide into organic matter through chemolithoautotrophic processes (which is similar to photosynthesis, but powered by chemical energy instead of sunlight). This value is important because it provides a baseline for understanding the size of the base of the food web in the subsurface, just as photosynthesis does at the surface of the Earth. Through this project we also contributed to the recent description of the proteins used by iron-oxidizing bacteria to gain energy from growing on iron and oxygen under neutral pH conditions (essentially, growing by creating rust), which has eluded scientists for several decades. Additionally, we contributed to a growing body of knowledge about the diversity of microbial life below the seafloor, and how this develops as bottom seawater circulates through the ocean crust. Ultimately, the results of this project provide a clearer picture of the types of microbes living below the seafloor and how much energy and food they have available to grow, and these results can inform the search for life elsewhere in the Universe that may be supported by growing on rocks. This project also contributed to the training and professional development of several students (one female and one male undergraduate, one male Masters student, and two male PhD students, both from underrepresented minorities) and two postdocs, one male and one female. A feature-length, award-winning documentary about the science involved in this project – North Pond: The Search for Intraterrestrials­ – is also freely available online, and a free interactive e-book featuring some of the scientists involved in this project – Where Wild Microbes Grow – is available online as well. Last Modified: 10/29/2015 Submitted by: Jason B Sylvan