Award: OCE-1029242

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. Last Modified: 11/24/2014 Submitted by: Gregory J Dick