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Project Progress

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.