Primary productivity is the transformation of chemical or solar energy to biomass and supports all life on earth. Photosynthesis is light-dependent productivity that uses sunlight’s energy to fix inorganic carbon into biomass. However, some bacteria and archaea are chemosynthetic and use chemical energy for the conversion of inorganic carbon to biomass. One can measure primary productivity as the rate of carbon fixation, i.e. the rate at which inorganic carbon is converted to organic carbon.
Previously, the highest carbon fixation rates have been measured in photosynthetic ecosystems, but the discovery of deep-sea hydrothermal vents in 1977 redefined our notions about life on earth and about biological primary productivity. These underwater hot springs discharge chemically altered seawater at temperatures up to 350°C through cracks in the earth’s crust. Vent effluents support substantial chemoautotrophic communities that use chemical energy to fix inorganic compounds for growth and biosynthesis. The first chemoautotrophic symbiosis to be described was the giant vent tubeworm Riftia pachyptila.
Interestingly, Riftia appears to be the fastest growing organism on Earth despite being mouthless, gutless, and entirely reliant on its symbionts for nutrition. In light of these observations, Riftia’s symbionts must be capable of supporting the growth of this assocation by sustaining extremely high carbon fixation rates (which is a direct index of primary productivity). The goal of this project is to identify the assemblage of host genes that govern primary productivity and, subsequently, organismal growth and community productivity. The results will produce insights into the molecular mechanisms that govern the productivity of a chemoautotrophic symbiosis, arguably the most productive symbiosis described to date. Via high-throughput expressed sequence tag (EST) sequencing, this project will aid in characterizing the host transcriptome responsible for stimulating rapid carbon fixation and sequestration as organic matter.
Principal Investigators: Peter R. Girguis and Spencer V. Nyholm (Harvard Univ.).