HR: 11:05h
AN: B22A-03    [Abstracts]
TI: A Modeling Comparison of Methanogenesis from Noncompetitive vs Competitive Substrates in a Simulated Hypersaline Microbial Mat
AU: * Decker, K L
EM: kdecker@mail.arc.nasa.gov
AF: California State University - Monerey Bay, MS 242-4 NASA-Ames Research Center, Moffett Field, CA 94032
AU: Potter, C
EM: cpotter@mail.arc.nasa.gov
AF: Ecosystem Science and Technology, NASA-Ames Research Center, Moffett Field, CA 94035
AU: Hoehler, T
EM: thoehler@mail.arc.nasa.gov
AF: Exobiology, NASA-Ames Research Center, Moffett Field, CA 94032
AB: The well-documented assumption about methanogens that co-occur in hypersaline mat communities with sulfate-reducing bacteria (SRB) is that they rely entirely on non-competitive substrates for methanogenesis. The reason for this is that during sulfate reduction, sulfur-reducing bacteria efficiently utilize H₂, leaving a concentration too low for methanogenesis. Early results from recent work on a hypersaline microbial mat from salt evaporation ponds of Guerrero Negro, Baja, Mexico cast doubt that methanogenesis only occurs via non-competitive substrates, because it shows an excess of H₂ in the mat rather than a paucity. We explore the use of our simulation model of the microbial biogeochemistry of a hypersaline mat (named MBGC) to compare methane production rates in a 1 cm thick mat when the methanogens use competitive substrates versus noncompetitive substrates. In the `non-competitive substrate' version of the model, methanogens rely exclusively on methylated amines that are accumulated as compatible solutes in cyanobacteria and released after lysis. In contrast, the `competitive substrate' models examine methanogen use of substrates (such as H₂ + acetate) with different SRB population sizes (from absent to low). The comparison of these models of methane and sulfide biogeochemistry of a hypersaline mat has both ecological and geobiological significance, as one hypothesis of Archean microbial mats is that they existed in a low sulfate environment.
DE: 0406 Astrobiology and extraterrestrial materials
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
SC: Biogeosciences [B]
MN: Fall Meeting 2005