White Paper Title: 
Examining the Distribution of Functional Capacity and Metabolic Activity of Endolithic Microbial Communities within Hydrothermal Vent Structures

The high diversity of vent-hosted microbes, their substantial biomass, and the timescale on which water circulates through hydrothermal vents suggest that these microbial communities likely contribute significantly to global biogeochemical cycling. However, the ecology of hydrothermal vent microbial communities and the broader impact of these organisms on marine biogeochemical cycles is poorly constrained. Based on chemical and thermodynamic models, specific metabolic pathways have been predicted to dominate these systems but few have been experimentally confirmed (McCollum and Shock, 1997). To date, we have a limited understanding of which biogeochemical reactions occur within chimney structures, the kinetics of these processes, the influence of these processes on the microbial community structure, and the extent to which they influence various marine or global elemental cycles.

In order to investigate these questions, the functional capacity and metabolic activity of these communities must be characterized. The study of environmental constraints on microbial colonization within active sulfide structures has been limited by the lack of assessments of in situ conditions in conjunction with microbial distribution within single structures. Advances in sampling and sequencing technologies are continuously allowing better characterization of the biogeochemical impact of these microorganisms within hydrothermal vent environments.  An in situ incubation instrument (recently developed with Deb Kelley) allows for the characterization of microbial communities in the context of long-term co-registered measurements of temperature and fluid chemistry. Our ongoing integration of metagenomic data with metabolic rate measurements aims to examine the key environmental and energetic parameters for microbial community assembly in hydrothermal sulfide environments.

While our knowledge of vent environments has grown considerably, many questions remain regarding the abundance, distribution, and metabolic characteristics of these endolithic communities. With the development of new molecular tools and innovative sampling devices, a more in depth analysis of these communities will begin to answer questions about the role of these systems in global biogeochemical cycles.  The complexity of these environments requires a multidisciplinary approach to correlate fluid chemistry, mineralogy and geology with microbiology at all levels of resolution.  Only then will we begin to constrain the biogeochemical impact of hydrothermally hosted vent microorganisms.