You are here

Unique Ecophysiology among U(VI)-Reducing Bacteria as Revealed by Evaluation of Oxygen Metabolism in Anaeromyxobacter dehalogenans Strain 2CP-C

TitleUnique Ecophysiology among U(VI)-Reducing Bacteria as Revealed by Evaluation of Oxygen Metabolism in Anaeromyxobacter dehalogenans Strain 2CP-C
Publication TypeJournal Article
Year of Publication2010
AuthorsThomas, SH, Sanford, RA, Amos, BK, Leigh, MBeth, Cardenas, E, Loffler, FE
JournalApplied and Environmental Microbiology
Pagination176–183
Abstract

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.

Username Tag: