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Unique Ecophysiology among U(VI)-Reducing Bacteria as Revealed by Evaluation of Oxygen Metabolism in Anaeromyxobacter dehalogenans Strain 2CP-C
|Title||Unique Ecophysiology among U(VI)-Reducing Bacteria as Revealed by Evaluation of Oxygen Metabolism in Anaeromyxobacter dehalogenans Strain 2CP-C|
|Publication Type||Journal Article|
|Year of Publication||2010|
|Authors||Thomas, SH, Sanford, RA, Amos, BK, Leigh, MBeth, Cardenas, E, Loffler, FE|
|Journal||Applied and Environmental Microbiology|
Anaeromyxobacter spp. respire soluble hexavalent uranium, U(VI), leading to the formation of insolubleU(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 sitefollowing biostimulation, but the susceptibility of the reduced material to oxidants (i.e., oxygen) compromiseslong-term U immobilization. Following oxygen intrusion, attached Anaeromyxobacter dehalogenans cells increasedapproximately 5-fold from 2.2 107 8.6 106 to 1.0 108 2.2 107 cells per g of sedimentcollected from well FW101-2. In the same samples, the numbers of cells of Geobacter lovleyi, a population nativeto area 3 and also capable of U(VI) reduction, decreased or did not change. A. dehalogenans cells captured viagroundwater sampling (i.e., not attached to sediment) were present in much lower numbers (<1.3 104 1.1 104 cells per liter) than sediment-associated cells, suggesting that A. dehalogenans cells occur predominantlyin association with soil particles. Laboratory studies confirmed aerobic growth of A. dehalogenans strain2CP-C at initial oxygen partial pressures (pO2) at and below 0.18 atm. A negative linear correlation [ (0.09 pO2) 0.051; R2 0.923] was observed between the instantaneous specific growth rate and pO2,indicating that this organism should be classified as a microaerophile. Quantification of cells during aerobicgrowth revealed that the fraction of electrons released in electron donor oxidation and used for biomassproduction (fs) decreased from 0.52 at a pO2 of 0.02 atm to 0.19 at a pO2 of 0.18 atm. Hence, the apparentfraction of electrons utilized for energy generation (i.e., oxygen reduction) (fe) increased from 0.48 to 0.81 withincreasing pO2, suggesting that oxygen is consumed in a nonrespiratory process at a high pO2. The ability totolerate high oxygen concentrations, perform microaerophilic oxygen respiration, and preferentially associatewith 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.