Collaborative Research: Influence of pressure on microbial communities in subseafloor sediment at hadal, abyssal, bathyal, and shelf water depths

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The globe-spanning realm of subseafloor sediment is Earth’s least-explored large biome. This project addresses a fundamental question about the microbial communities that inhabit the subseafloor sedimentary environment – to what extent and in what ways are they adapted to the low temperature, high pressure conditions where they are found? Or, alternatively, are they just accidentally introduced from the shallower and lower-pressure world where the organic matter that feeds them largely originates? This project is examining how these organisms metabolize organic matter in sediments. The project is also advancing the development of a diverse, globally competitive workforce in science, technology, engineering, and mathematics (STEM). It introduces 10 or more students to sea-going research, by including them as shipboard scientists. The project especially focusses on creating and funding opportunities for students from minority groups under-represented in STEM fields, students from economically disadvantaged backgrounds, and students from Puerto Rico, and from multiple educational stages (ranging from community college to graduate school), with diverse STEM interests. Study of samples and data from the expedition are central to graduate and undergraduate research by students from these multiple institutions. The project also supports the broader science community by collecting and providing diverse samples for additional studies, including, but not limited to, studies of deep-water residence time in a deep-sea trench, past oceanographic conditions, and subseafloor microbes. The fundamental objective of this project is to determine how the subseafloor microbial communities and activities across a gradient of oceanic depth zones (sublittoral, bathyal, abyssal, hadal) are impacted by the pressure of the surrounding water. The primary hypothesis being tested is that “microbial communities in subseafloor sediment are adapted for in situ pressure.” The null hypothesis is that these “communities are merely remnant populations introduced from shallower depths and poorly adapted for in situ pressure.” To test these hypotheses, the project compares the subseafloor communities and rates of activity that occur in anoxic subseafloor sediment at ocean depths ranging from 50 to ~8400 meters below sea level in the Puerto Rico Trench region. To collect the samples and shipboard data, the project includes a 26-day coring program. The project interrogates the genomic composition and community metabolic rates of the subseafloor sedimentary communities over this full range of ocean depths. Experiments are being conducted to determine the pressure-dependence of potential processes (sulfate reduction and methanogenesis) and genes that are preferentially expressed at in situ pressures by sublittoral, bathyal, abyssal and hadal subseafloor communities. These results are synthesized to identify the nature and extent of adaptations to in situ pressure in subseafloor communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.