Intellectual merit. Deep-sea hydrothermal vent plumes are globally distributed along the 60,000-km mid-ocean ridge system and are hot spots of microbial biogeochemistry in the deep oceans. These plumes play host to important interactions between microbial communities and hydrothermal inputs; hydrothermal energy sources stimulate enhanced microbial activity and productivity, and microorganisms mediate the flux of elements and energy from deep-sea hydrothermal vents into the oceans. This hydrothermal flux is a significant source of two key micronutrients, iron and manganese, for the oceans. Despite this importance, microbial communities in deep sea-hydrothermal plumes have been understudied relative to those inhabiting near-vent and subsurface environments. The overall goal of this project is to reveal the microbial community dynamics responsible for enhanced microbial activities and mediation of geochemical processes that has been observed in deep-sea hydrothermal plumes. This research project is focused on plumes in the Guaymas Basin (Gulf of California), where previous results showed dramatic enhancement of microbial activity and enzymatic manganese (II) oxidation relative to the ambient deep sea. Cutting-edge DNA sequencing technologies will be utilized to characterize the microbial diversity, metabolic potential and physiological state of plume versus background communities through metagenomics and metatranscriptomics. The specific objectives are (1) to utilize hundreds of thousands of rRNA gene sequences available from DNA and RNA to compare community structure and population-specific activity in plumes versus background; (2) to reconstruct composite genomes from the most abundant deep-sea microbial populations and evaluate their metabolic capabilities and nutritional needs; and (3) to quantitatively compare gene content and expression profiles in plume and background, with a focus on uncovering metabolic shifts towards chemolithoautotrophy. Overall, results are expected to shed light on the nature of microbial players and processes in plumes: is plume biogeochemistry mediated by indigenous deep-sea microorganisms that have been stimulated by hydrothermal inputs, or by plume-specific groups that were entrained from near-vent environments?
Broader impacts. The project will have broad impacts at several levels. First, the research will bring together students (undergraduate and graduate) and faculty from geosciences, microbial ecology, and bioinformatics to investigate an interdisciplinary problem. Second, methods for statistical and computational analysis of large-scale environmental DNA sequencing that are currently hindering the potential of emerging DNA sequencing technologies will be advanced and made publicly accessible with open source programs, online support, and documentation. Third, research activities will be intimately integrated into public outreach activities. An existing collaboration between the PI and education professionals at the University of Michigan's IDEA Institute will be expanded to develop a summer camp in the geosciences for high school students. This two-week summer camp will enable hands-on experiences and learning activities for high school students and teachers from Ypsilanti and Detroit, MI public schools, which are home to many potential future scientists from underrepresented groups.
The goal of this project was to understand the interplay between microbiology and geochemistry at deep-sea hydrothermal vents. Here, hot water that is enriched with chemicals such as sulfur, iron, methane, and ammonium is injected into the cold, dark, waters of the deep sea, forming hydrothermal plumes that rise off the sea floor. Specific questions were: (1) How does the chemistry of hydrothermal fluids shape the composition and metabolism of microbial communities in hydrothermal plumes? (2) How does microbial activity influence the chemistry of deep-sea hydrothermal plumes? These questions were addressed in the Guaymas Basin of the Gulf of California. The genome and transcriptome sequences of dominant plume bacteria and archaea were reconstructed, yielding insights into the metabolism of these plume microorganisms. We found that sulfur, ammonia, and methane were the primary energy sources for microbial growth in the plume. Interestingly, many plume microbes were found to be metabolically versatile, meaning they can use multiple different resources for energy. In particular, the sulfur oxidizing bacterium SUP05 was found to use both sulfur and hydrogen as sources of energy. This indicates that the SUP05 bacteria have a flexible genome and metabolism, tuning them to the environment. We also found that archaea dominate the portion of the microbial community that oxidizes ammonia. This was unexpected because at high ammonia concentrations bacteria are typically thought to predominate. In terms of how microorganisms influence the chemistry of hydrothermal plumes, two major discoveries were made. First, a wide variety of novel genes involved in the breakdown of hydrocarbons were identified. These genes are substantially different from known genes involved in hydrocarbon oxidation, highlighting our current lack of knowledge on the breakdown of natural hydrocarbons in the oceans. Second, we found that genes involved in cellular uptake of iron were highly transcribed in the plume. This is important because it indicates that microbes may be converting iron from relatively immobile and unavailable forms like iron oxides to relatives mobile and bio-available forms. This suggests that microbes may substantially influence the form of iron at vents, thus affecting its fate in the deep ocean. Overall, this project resulted in 10 published papers in peer-reviewed journals and one article in a professional society magazine.
