HR: 10:35h
AN: B22D-02 [Abstracts]
TI: Anaerobic Nitrate-Dependent Metal Bio-Oxidation
AU: * Weber, K
EM: kweber@nature.berkeley.edu
AF: Plant and Microbial Biology, University of California, Berekeley, CA 94720-3102,
AU: Knox, T
EM: traci.knox@gmail.com
AF: Plant and Microbial Biology, University of California, Berekeley, CA 94720-3102,
AU: Achenbach, L A
EM: laurie@micro.siu.edu
AF: Department of Microbiology, Southern Illinois University, Carbondale, IL 62901-6508,
AU: Coates, J D
EM: jcoates@nature.berkeley.edu
AF: Plant and Microbial Biology, University of California, Berekeley, CA 94720-3102,
AB:
Direct biological oxidation of reduced metals (Fe(II) and U(IV)) coupled to nitrate reduction at circumneutral pH
under anaerobic conditions has been recognized in several environments as well as pure culture. Several
phylogentically diverse mesophilic bacteria have been described as capable of anaerobic, nitrate-dependent
Fe(II) oxidation (NFOx). Our recent identification of a freshwater mesophilic, lithoautotroph, Ferrutens
nitratireducens strain 2002, capable of growth through NFOx presents an opportunity to further study metal bio-
oxidation. Continuing physiological studies revealed that in addition to Fe(II) oxidation, strain 2002 is capable of
oxidizing U(IV) (4 μM) in washed cell suspensions with nitrate serving as the electron acceptor. Pasteurized
cultures exhibited abiotic oxidation of 2 μM U(IV). Under growth conditions, strain 2002 catalyzed the
oxidation of 12 μM U(IV) within a two week period. Cultures amended with sodium azide, an electron
transport inhibitor, demonstrated limited oxidation (7 μM) similar to pasteurized cultures, supporting the
direct role of electron transport in U(IV) bio-oxidation. The oxidation of U(IV) coupled denitrification at
circumneutral pH would yield enough energy to support anaerobic microbial growth (ΔG°'= -460.36
kJ/mole). It is currently unknown whether or not strain 2002 can couple this metabolism to growth. The growth of
F. nitratireducens strain 2002 utilizing Fe(II) as the sole electron donor was previously demonstrated. The
amount of U(IV) (~12 μM) that strain 2002 oxidized under similar autotrophic growth conditions yields 0.0019
kJ, enough energy for the generation of ATP (5.3 x 10-20 kJ ATP-1), but not enough energy for cell
replication as calculated for nitrate-dependent Fe(II) oxidizing conditions (0.096 kJ) assuming a similar
metabolism. In addition to F. nitratireducens strain 2002, a nitrate-dependent Fe(II) oxidizing bacterium
isolated from U contaminated groundwater, Diaphorobacter sp. strain TPSY, was also capable of nitrate-
dependent U(IV) oxidation (8 μM over 24 hours, pseudo first order rate constant of 0.12 ± 0.02 hr-1)
in washed cell suspensions. Further biochemical investigation of nitrate-dependent U(IV) oxidation in strain
TPSY revealed the expression of several putative high molecular weight proteins specific to this metabolism.
Together with the previously described metabolic ability of Geobacter metallireducens (Finneran et al. 2002)
and Thiobacillus denitrificans (Beller 2005), these data indicate that anaerobic, metal oxidation may be a
ubiquitous microbial metabolism.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0418 Bioremediation
DE: 0419 Biomineralization
DE: 0448 Geomicrobiology
DE: 0463 Microbe/mineral interactions
SC: Biogeosciences [B]
MN: 2007 Fall Meeting