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.

Microbial Community Changes in Response to Ethanol or Methanol Amendments for U(VI) Reduction

“…requires H 2 as an electron donor, which cannot be replaced by acetate (71). Thus, acetate and H 2 may serve as electron donors for U(VI) reduction by species of Geobacter and Amaeromyxobacter (55,71).…”

“…Various substrates (e.g., acetate, ethanol, glucose, and methanol) have been used either in the field or in microcosm studies, and most were capable of stimulating microbial U(VI) reduction (1,8,42,43,47,60); however, the addition of methanol did not always result in U(VI) reduction (49). Many microorganisms are known to reduce U(VI) in pure culture, including a hyperthermophilic archaeon (28), a thermophilic bacterium Thermoterrabacterium ferrireducens (29), the mesophilic dissimilatory metal-reducing bacteria Geobacter and Shewanella (67) and Anaeromyxobacter dehalogenans (71), the sulfate-reducing bacterium Desulfovibrio sp. (61), and fermentative bacteria such as Clostridium spp.…”

Microbial Communities in Contaminated Sediments, Associated with Bioremediation of Uranium to Submicromolar Levels

“…These sequences were related to the known U(VI) reducer A. dehalogenans (45) and to a clone from a uranium mine sediment where uranium reduction was demonstrated (38).…”

U(VI) reduction by spores of Clostridium acetobutylicum

“…(Khijniak et al, 2005). Also, among this variety of U(VI)-reducing bacteria, a subset (e.g., Anaeromyxobacter dehalogenans (Wu et al, 2006), Geobacter metallireducens, Shewanella putrefaciens (Lovley et al, 1991) and Desulfotomaculum reducens (Tebo and Obraztsova, 1998)) have been reported to conserve energy from this reaction, and to couple it to growth.…”

“…The biochemical mechanisms of microbial U(VI) reduction have been extensively studied for organisms belonging to the Desulfovibrio (Payne et al, 2004), Shewanella (BencheikhLatmani et al, 2005), Geobacter (Shelobolina et al, 2007) and Anaeromyxobacter (Wu et al, 2006) genera. However, these biochemical models may not apply to the whole spectrum of bacteria capable of this reaction, which comprises not only many other mesophilic Proteobacteria, but also Firmicutes e both sulfate-reducing and fermentative e e.g., Clostridium spp.…”