Microbial processes in extreme environments
September 6, 2013
The weather made for a tough day for the science crew today. Forced from their choice dive site by high winds, the group chose to dive closer to shore, just south of Cape Mendocino. High winds in that area, too, forced an end to the ROV dive after just a few hours of exploring a relatively featureless sandy bottom, and the scientists turned their attention to their indoor-lab work for the rest of the day.
Working alongside the MBARI chemistry team on this expedition are two biogeochemists. Postdoctoral Researcher Lindsey Fields and Ph.D. student Ryan Sibert. Both work in Samantha Joye’s lab at the University of Georgia. Their work meshes well with the Brewer group’s as they are studying the biogeochemical processes at the same sites that Brewer and his team visit.
Lindsey currently researches the nitrogen cycle, or the addition, removal, and transformation of this important element. She focuses her efforts on sampling deep-sea extreme environments, such as brine and/or oil and gas seeps. During this cruise, Lindsey is collecting sediment cores during remotely operated vehicle dives near gas vents in the Eel River Basin.
Understanding the marine nitrogen cycle is of vital importance because it influences the cycling of other elements (such as carbon, phosphorus, and oxygen), and is an essential nutrient for biological production. The nitrogen cycle is relatively complex, and processes are driven largely by microbial activities. To measure these activities, Lindsey collects samples of water and sediment that she incubates. She measures process rates during incubations using stable nitrogen isotope (15N) tracers. These isotopes are used to label various forms of nitrogen, and are traced throughout the incubations to determine which processes are occurring.
Making measurements in extreme habitats provides insight both to the contributions of these environments to global elemental cycles, and to earlier forms of life on earth. Organisms that thrive in extreme environments require special adaptations to their habitats, and as such, these areas provide an opportunity to learn about unique microbes and their roles in nitrogen cycling
— Lindsey Fields and Nancy Barr
My research focuses primarily on microbial carbon and sulfur cycling in deep ocean brine pools, oil seeps, and oxygen-poor sediments. I am specifically interested in rates of microbial methane production and consumption (technically: anaerobic oxidation of methane), as well as microbial sulfate consumption rates in marine sediments and brines. Although methane makes up a substantially smaller fraction of the total atmospheric greenhouse gas budget than carbon dioxide (CO2), it is nearly 25 times more effective at trapping heat than CO2 alone. Much of the methane we see in the atmosphere today is the direct result of microbial metabolisms at work in environments with little to no oxygen (anoxic environments). Organisms that utilize methane as a food source (anaerobic methanotrophs) in marine settings are believed to consume a substantial portion of methane produced in oxygen-poor seafloor sediments, regardless of the methane source. Sulfur availability plays a key role in methane-based metabolisms, so our lab carefully measures rates of sulfate (a major dissolved component of seawater) consumption alongside rates of methane consumption. All told, organisms that produce and consume methane are major players in global temperature regulation and deeply influence the flow of sulfur and carbon in marine settings.
While my work typically leads me to the brine pools and oil seeps of the Gulf of Mexico, my work aboard the R/V Western Flyer will focus on microbial carbon and sulfur cycling in the oil and gas seeps found along the Eel River Basin. The evolutionary history of oil and gas formation in the Gulf of Mexico is heavily influenced by the movement of buried sheets of salt and the rates of organic matter input. The transform faults and subduction zones of the Northern Pacific create a slightly different geologic setting that may influence the distribution of microbial communities within the sediments of the area, yielding a unique ecology that is substantially different than that of the Gulf ecosystem. Calculating methane production rates, anaerobic oxidation of methane rates, and sulfate reduction rates here allows us to refine our understanding of elemental flows of carbon and sulfur globally, compare rates in different environmental settings, and may provide insight into new or novel microbial metabolic pathways.
— Ryan Sibert