title: Unique ecophysiology among U(VI)-reducing bacteria as revealed by evaluation of oxygen metabolism in Anaeromyxobacter dehalogenans strain 2CP-C.
abstract: Anaeromyxobacter spp. respire soluble hexavalent uranium, U(VI), leading to the formation of insoluble U(IV), and are present at the uranium-contaminated Oak Ridge Integrated Field Research Challenge (IFC) site. Pilot-scale in situ bioreduction of U(VI) has been accomplished in area 3 of the Oak Ridge IFC site following biostimulation, but the susceptibility of the reduced material to oxidants (i.e., oxygen) compromises long-term U immobilization. Following oxygen intrusion, attached Anaeromyxobacter dehalogenans cells increased approximately 5-fold from 2.2x10(7)+/-8.6x10(6) to 1.0x10(8)+/-2.2x10(7) cells per g of sediment collected from well FW101-2. In the same samples, the numbers of cells of Geobacter lovleyi, a population native to area 3 and also capable of U(VI) reduction, decreased or did not change. A. dehalogenans cells captured via groundwater sampling (i.e., not attached to sediment) were present in much lower numbers (<1.3x10(4)+/-1.1x10(4) cells per liter) than sediment-associated cells, suggesting that A. dehalogenans cells occur predominantly in association with soil particles. Laboratory studies confirmed aerobic growth of A. dehalogenans strain 2CP-C at initial oxygen partial pressures (pO2) at and below 0.18 atm. A negative linear correlation [micro=(-0.09xpO2)+0.051; R2=0.923] was observed between the instantaneous specific growth rate micro and pO2, indicating that this organism should be classified as a microaerophile. Quantification of cells during aerobic growth revealed that the fraction of electrons released in electron donor oxidation and used for biomass production (fs) decreased from 0.52 at a pO2 of 0.02 atm to 0.19 at a pO2 of 0.18 atm. Hence, the apparent fraction of electrons utilized for energy generation (i.e., oxygen reduction) (fe) increased from 0.48 to 0.81 with increasing pO2, suggesting that oxygen is consumed in a nonrespiratory process at a high pO2. The ability to tolerate high oxygen concentrations, perform microaerophilic oxygen respiration, and preferentially associate with soil particles represents an ecophysiology that distinguishes A. dehalogenans from other known U(VI)-reducing bacteria in area 3, and these features may play roles for stabilizing immobilized radionuclides in situ.
authors.affiliation: Georgia Institute of Technology, School of Civil and Environmental Engineering, 311 Ferst Drive, 3228 ES&T Building, Atlanta, GA 30332-0512, USA.
authors.forename: Sara H
authors.initials: SH
authors.lastname: Thomas
authors.forename: Robert A
authors.initials: RA
authors.lastname: Sanford
authors.forename: Benjamin K
authors.initials: BK
authors.lastname: Amos
authors.forename: Mary Beth
authors.initials: MB
authors.lastname: Leigh
authors.forename: Erick
authors.initials: E
authors.lastname: Cardenas
authors.forename: Frank E
authors.initials: FE
authors.lastname: Löffler
mesh_terms: D000332:Aerobiosis; D015169:Colony Count, Microbial; D004583:Electrons; D004734:Energy Metabolism; D045302:Geobacter / Q000302:isolation & purification; D009231:Myxococcales / Q000254:growth & development / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D014501:Uranium / Q000378:metabolism*; D014871:Water Microbiology
chemical_list: D014501:Uranium; D010100:Oxygen