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Dynamics of Molecular Hydrogen in Hypersaline Microbial MarsEarly Earth microbial communities that centered around the anaerobic decomposition of organic molecular hydrogen as a carrier of electrons, regulator of energy metabolism, and facilitator of syntroph'c microbial interactions. The advent of oxygenic photosynthetic organisms added a highly dynamic and potentially dominant term to the hydrogen economy of these communities. We have examined the daily variations of hydrogen concentrations in cyanobacteria-dominated microbial mats from hypersaline ponds in Baja California Sur, Mexico. These mats bring together phototrophic and anaerobic bacteria (along with virtually all other trophic groups) in a spatially ordered and chemically dynamic matrix that provides a good analog for early Earth microbial ecosystems. Hydrogen concentrations in the photic zone of the mat can be three orders of magnitude or more higher than in the photic zone, which are, in turn, an order of magnitude higher than in the unconsolidated sediments underlying the mat community. Within the photic zone, hydrogen concentrations can fluctuate dramatically during the diel (24 hour day-night) cycle, ranging from less than 0.001% during the day to nearly 10% at night. The resultant nighttime flux of hydrogen from the mat to the environment was up to 17% of the daytime oxygen flux. The daily pattern observed is highly dependent on cyanobacterial species composition within the mat, with Lyngbya-dominated systems having a much greater dynamic range than those dominated by Microcoleus; this may relate largely to differing degrees of nitrogen-fixing and fermentative activity in the two mats. The greatest H2 concentrations and fluxes were observed in the absence of oxygen, suggesting an important potential feedback control in the context of the evolution of atmospheric composition. The impact of adding this highly dynamic photosynthetic term to the hydrogen economy of early microbial ecosystems must have been substantial. From an evolutionary standpoint, the H2 generated in mats could have represented a very important new source of electrons and energy - but one that could not be harnessed without substantial adaptation to the highly variable chemistry of the mat surface. In addition, the emergent chemistry of anaerobic communities is often highly dependent on ambient hydrogen concentrations, so that incorporation of these communities into photosynthetic mats could have significantly affected the composition and flux of reduced "biosignature' gases to the environment.
Document ID
20010000044
Acquisition Source
Ames Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Hoehler, Tori M.
(NASA Ames Research Center Moffett Field, CA United States)
Bebout, Brad M.
(NASA Ames Research Center Moffett Field, CA United States)
Visscher, Pieter T.
(NASA Ames Research Center Moffett Field, CA United States)
DesMarais, David J.
(NASA Ames Research Center Moffett Field, CA United States)
DeVincenzi, Donald L.
Date Acquired
August 20, 2013
Publication Date
January 1, 2000
Subject Category
Life Sciences (General)
Meeting Information
Meeting: Astrobiology Science
Location: Moffett Field, CA
Country: United States
Start Date: April 3, 2000
End Date: April 5, 2000
Funding Number(s)
PROJECT: RTOP 344-38-32-03
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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