In Situ Measurement of Rates of Chemoautotrophic Carbon Production at Deep-Sea Hydrothermal Vents
Craig Taylor (PI, Biology, WHOI)
Jeremy Rich (Co-PI, Brown University)
Nadine Le Bris (Banyuls-sur-Mer, France)
Knowledge of the in situ metabolism of microorganisms carrying out CO2-fixation at deep-sea hydrothermal vents is very limited. Particularly lacking are studies measuring rates of autotrophic carbon fixation in situ, which is a measurement ultimately needed to constrain production in these ecosystems. Although recent data suggests that nitrate reduction either to N2 (denitrification) or to NH4+ (dissimilatory reduction of nitrate to ammonium, DNRA) might be responsible for a significant fraction of chemoautotrophic production, NO3--reduction rates have never been measured in situ at hydrothermal vents. We hypothesize that chemoautrophic growth is strongly coupled to nitrate respiration in vent microbial communities.
Here, we propose to develop a Vent-Time Series Submersible Incubation Device (Vent-TSSID), a robotic micro-laboratory for routine application by the oceanographic community for measuring rates of relevant metabolic processes at hydrothermal vents at both in situ pressures and temperatures.
The key modifications/developments required for the Vent-TSSID are 1) combining the capabilities of two existing instrumentation, the TSSID and the McLane Res. Labs Remote Access Sampler (RAS), into a single robotic micro-laboratory, 2) developing twin temperature-controlled incubation chambers to mimic the physical conditions within warm water hydrothermal vent fluids being sampled at the sea floor andwhich likely exists deeper within the vent system, 3) development of a modified incubation chamber piston that will allow quasi-steady state introduction of dissolved oxygen gas and/or dissolved hydrogen gas into the incubating sample & will provide gentle stirring of the chamber contents for efficient temperature control, and 4) incorporating newly designed FF2 fixation filter units into the Vent-TSSID that will allow preservation of samples on a time scale relevant to gene expression studies of collected particulate samples.
After having completed the development and testing of the components required to be able to use the Vent-TSSID, we propose to use this instrument to its full advantage by tackling the following currently unresolved science objectives: 1) obtain in situ rates of chemoautotrophic carbon fixation, 2) obtain in situ nitrate reduction rate measurements, and 3) directly correlate the measurement of these processes with the expression of key genes involved in carbon and energy metabolism.
We propose one cruise that will take place approximately 16 months into the project (~Jan’13). We plan for a total of 5 deployments of the Vent-TSSID as well as ancillary sampling collection at the 9°46’N to 9°53’N segment of the East Pacific Rise (EPR). In particular, we propose to focus our efforts on ‘Crab Spa’, a diffuse flow vent site (fluid exit temperatures ~25°C) that has been used by the PIs as a model system to gain insights into chemoautotrophic processes and has been frequently sampled over the last several years. This vent site has been very well characterized, both geochemically and microbiologically, providing excellent background data for the proposed process oriented studies. We propose to perform a number of short duration time-course incubations to assess the role of different environmental parameters that we have identified as likely key variables (e.g., O2, H2, temperature, NO3-, sulfide), and to link these process rate measurements to the expression of functional genes using a functional gene array (GeoChip). This study will be the first attempt to measure critical metabolic processes of hydrothermal vent microbial assemblages under critical in situ conditions and to assess the quantitative importance of electron donor and acceptor pathways in situ. Quantifying rates at deep-sea vent ecosystems is critical for assessing their impact on global biogeochemical cycles.
This project is just starting and is funded by the Ocean Technology and Interdisciplinary Coordination program within the Ocean Science Disvision of NSF.