Dataset Information

Uranium(VI) reduction by Anaeromyxobacter dehalogenans strain 2CP-C.

ABSTRACT: Previous studies demonstrated growth of Anaeromyxobacter dehalogenans strain 2CP-C with acetate or hydrogen as the electron donor and Fe(III), nitrate, nitrite, fumarate, oxygen, or ortho-substituted halophenols as electron acceptors. In this study, we explored and characterized U(VI) reduction by strain 2CP-C. Cell suspensions of fumarate-grown 2CP-C cells reduced U(VI) to U(IV). More-detailed growth studies demonstrated that hydrogen was the required electron donor for U(VI) reduction and could not be replaced by acetate. The addition of nitrate to U(VI)-reducing cultures resulted in a transitory increase in U(VI) concentration, apparently caused by the reoxidation of reduced U(IV), but U(VI) reduction resumed following the consumption of N-oxyanions. Inhibition of U(VI) reduction occurred in cultures amended with Fe(III) citrate, or citrate. In the presence of amorphous Fe(III) oxide, U(VI) reduction proceeded to completion but the U(VI) reduction rates decreased threefold compared to control cultures. Fumarate and 2-chlorophenol had no inhibitory effects on U(VI) reduction, and both electron acceptors were consumed concomitantly with U(VI). Since cocontaminants (e.g., nitrate, halogenated compounds) and bioavailable ferric iron are often encountered at uranium-impacted sites, the metabolic versatility makes Anaeromyxobacter dehalogenans a promising model organism for studying the complex interaction of multiple electron acceptors in U(VI) reduction and immobilization.

SUBMITTER: Wu Q

PROVIDER: S-EPMC1472366 | biostudies-literature | 2006 May

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Uranium(VI) reduction by Anaeromyxobacter dehalogenans strain 2CP-C.

Wu Qingzhong Q Sanford Robert A RA Löffler Frank E FE

Applied and environmental microbiology 20060501 5

Previous studies demonstrated growth of Anaeromyxobacter dehalogenans strain 2CP-C with acetate or hydrogen as the electron donor and Fe(III), nitrate, nitrite, fumarate, oxygen, or ortho-substituted halophenols as electron acceptors. In this study, we explored and characterized U(VI) reduction by strain 2CP-C. Cell suspensions of fumarate-grown 2CP-C cells reduced U(VI) to U(IV). More-detailed growth studies demonstrated that hydrogen was the required electron donor for U(VI) reduction and coul ...[more]

PMID: 16672509

Similar Datasets

Project description: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.

Project description:The versatile soil bacterium Anaeromyxobacter dehalogenans lacks the hallmark denitrification genes nirS and nirK (NO2-?NO), and couples growth to NO3- reduction to NH4+ (respiratory ammonification) and to N2O reduction to N2A. dehalogenans also grows by reducing Fe(III) to Fe(II), which chemically reacts with NO2- to form N2O (i.e., chemodenitrification). Following the addition of 100 ?moles of NO3- or NO2- to Fe(III)-grown, axenic cultures of A. dehalogenans, 54 (±7) ?moles and 113 (±2) ?moles N2O-N, respectively, were produced and subsequently consumed. The conversion of NO3- to N2 in the presence of Fe(II) through linked biotic-abiotic reactions represents an unrecognized ecophysiology of A. dehalogenans The new findings demonstrate that the assessment of gene content alone is insufficient to predict microbial denitrification potential and N loss (i.e., the formation of gaseous N products). A survey of complete bacterial genomes in the NCBI Reference Sequence database coupled with available physiological information revealed that organisms lacking nirS/nirK but with Fe(III) reduction potential and genes for NO3- and N2O reduction are not rare, indicating that NO3- reduction to N2 through linked biotic-abiotic reactions is not limited to A. dehalogenans Considering the ubiquity of iron in soils and sediments and the broad distribution of dissimilatory Fe(III) and NO3- reducers, denitrification independent of NO-forming NO2- reductases (through combined biotic-abiotic reactions) may have substantial contributions to N loss and N2O flux.Importance Current attempts to gauge N loss from soils rely on the quantitative measurement of nirK and nirS genes and/or transcripts. In the presence of iron, the common soil bacterium Anaeromyxobacter dehalogenans is capable of denitrification and producing N2 without the key denitrification genes nirK/nirS Such chemodenitrifiers denitrify through combined biotic and abiotic reactions and have potentially large contributions to N loss to the atmosphere, and fill a heretofore unrecognized ecological niche in soil ecosystems. The findings emphasize that comprehensive understanding of N flux and accurate assessment of denitrification potential can only be achieved when integrated studies of interlinked biogeochemical cycles are performed.

Project description:Anaeromyxobacter sp. strain PSR-1, a dissimilatory arsenate [As(V)]-reducing bacterium, can utilize As(V) as a terminal electron acceptor for anaerobic respiration. A previous draft genome analysis revealed that strain PSR-1 lacks typical respiratory As(V) reductase genes (arrAB), which suggested the involvement of another protein in As(V) respiration. Dissimilatory As(V) reductase activity of strain PSR-1 was induced under As(V)-respiring conditions and was localized predominantly in the periplasmic fraction. The activity was visualized by partially denaturing gel electrophoresis, and liquid chromatography-tandem mass spectrometry analysis identified proteins involved in the active band. Among these proteins, a protein annotated as molybdopterin-dependent oxidoreductase (PSR1_00330) exhibited the highest sequence coverage, 76%. Phylogenetic analysis revealed that this protein was a homolog of tetrathionate reductase catalytic subunit TtrA. However, the crude extract of strain PSR-1 did not show significant tetrathionate reductase enzyme activity. Comparative proteomic analysis revealed that the protein PSR1_00330 and a homolog of tetrathionate reductase electron transfer subunit TtrB (PSR1_00329) were expressed abundantly and specifically under As(V)-respiring conditions, respectively. The genes encoding PSR1_00330 and PSR1_00329 formed an operon-like structure along with a gene encoding a c-type cytochrome (cyt c), and their transcription was upregulated under As(V)-respiring conditions. These results suggest that the protein PSR1_00330, which lacks tetrathionate reductase activity, functions as a dissimilatory As(V) reductase in strain PSR-1. Considering the wide distribution of TtrA homologs among bacteria and archaea, they may play a hitherto unknown role along with conventional respiratory As(V) reductase (Arr) in the biogeochemical cycling of arsenic in nature.IMPORTANCE Dissimilatory As(V)-reducing prokaryotes play significant roles in arsenic release and contamination in groundwater and threaten the health of people worldwide. Generally, such prokaryotes reduce As(V) by means of a respiratory As(V) reductase designated Arr. However, some dissimilatory As(V)-reducing prokaryotes such as Anaeromyxobacter sp. strain PSR-1 lack genes encoding Arr, suggesting the involvement of other protein in As(V) reduction. In this study, using multiple proteomic and transcriptional analyses, it was found that the dissimilatory As(V) reductase of strain PSR-1 was a protein closely related to the tetrathionate reductase catalytic subunit (TtrA). Tetrathionate reductase is known to play a role in anaerobic respiration of Salmonella on tetrathionate, but strain PSR-1 showed neither growth on tetrathionate nor significant tetrathionate reductase enzyme activity. These results suggest the possibility that TtrA homologs encoded in a wide variety of archaeal and bacterial genomes might function as dissimilatory As(V) reductases.

Dataset Information

Uranium(VI) reduction by Anaeromyxobacter dehalogenans strain 2CP-C.

Publications

Uranium(VI) reduction by Anaeromyxobacter dehalogenans strain 2CP-C.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets