2015 Annual Science Report
VPL at University of Washington Reporting | JAN 2015 – DEC 2015
Biogenic Gases From Anoxygenic Photosynthesis in Microbial Mats
This lab and field project aims to measure biogenic gas fluxes in engineered and natural microbial mats composed of anoxygenic phototrophs and anaerobic chemotrophs, such as may have existed on the early Earth prior to the advent of oxygenic photosynthesis. The goal is to characterize the biogeochemical cycling of S, H, and C in an effort to constrain the sources and sinks of gaseous biosignatures that may be relevant to the detection of life in anoxic biospheres on habitable exoplanets.
Parenteau and UW Astrobiology graduate student Meg Smith performed experimental measurements of biogenic gases emitted from pure cultures of anoxygenic phototrophs, as well as from naturally occurring mats of anoxygenic phototrophs from sulfidic hot springs in Northern California (Fig. 1). Using a Hiden Membrane Inlet Mass Spectrometer (MIMS), we measured CO2 produced by the photoheterotrophic metabolism of purple non-sulfur bacteria. We also detected two mass fragments associated with currently unidentified biogenic sulfur gases. Interestingly, photoheterotrophy may be one of the earliest forms of photosynthesis on the early Earth because it can occur before the evolution of C fixation pathways (Blankenship, 2014). Given this photoheterotrophic metabolism, CO2 could be a biosignature gas that is underconsidered. With that said, CO2 is also produced by abiotic processes, so it is not clear whether biologic CO2 production would have represented a significant source of CO2 on the early Earth. These experiments are a critical, but early, step in characterizing biosignatures, and quantifying biogenic gas fluxes from anoxygenic photosynthetic bacteria.
PROJECT INVESTIGATORS:Niki Parenteau
PROJECT MEMBERS:Tori Hoehler
RELATED OBJECTIVES:Objective 4.1
Earth's early biosphere.
Co-evolution of microbial communities
Effects of environmental changes on microbial ecosystems
Biosignatures to be sought in nearby planetary systems