HR: 0800h
AN: OS21A-1207    [Abstracts]
TI: Thermodynamic control of microbial sulfate reduction rates and consequences for the form and distribution of metal sulfide nanoparticles
AU: * Jin, Q
EM: qjin@eps.berkeley.edu
AF: Department of Earth and Planetary Science, University of California at Berkeley, 307 McCone Hall #4767, Berkeley, CA 94720-4767 United States
AU: Banfield, J
EM: jill@eps.berkeley.edu
AF: Department of Earth and Planetary Science, University of California at Berkeley, 307 McCone Hall #4767, Berkeley, CA 94720-4767 United States
AB: Sulfate reducing bacteria are widespread in natural environment. They derive energy for growth by reducing sulfate to sulfide. In the presence of metal ions, the sulfide byproduct precipitates as metal sulfide nanoparticles. Microorganisms can reduce sulfate through two metabolic pathways, i.e., an incomplete and a complete pathway. In the former case, microorganisms, such as {\it Desulfovibrio} sp., oxidize lactate, butyrate, ethanol, etc. to acetate, whereas in the latter, microorganisms, such as {\it Desulfobacter} sp., oxidize acetate to bicarbonate. It is important to study the kinetics of microbial sulfate reduction because microbial metabolic rates may influence the form, mobility, and reactivity of biogenic minerals. The rate of sulfate reduction is controlled not only by substrate concentrations in environments, but also by the thermodynamic driving force. The driving force is the difference between the energy available from environment and the energy conserved. The amount of energy conserved is about 80 kJ/mol lactate and 90 kJ/mol acetate for incomplete and complete pathway, respectively. Where the energy available from environments is much higher than the energy conserved, the driving force is large and sulfate reduction proceeds at high rate. The particle size of metal sulfide minerals precipitated under such conditions is extremely small. However, where the energy available is close to the energy conserved, the driving force is small and the rate of sulfate reduction is small. These conditions could favor nanoparticle transport because particle advection and dispersion may be strong enough to remove nanoparticles before large immobile aggregates can form.
DE: 1045 Low-temperature geochemistry
DE: 0400 Biogeosciences
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting