Thermodynamic targeting of microbial perchlorate reduction by selective electron donors

Abstract

Here we describe 2,6-anthrahydroquinone disulfonate (AH 2 DS) as a model thermodynamically 'targeting' electron donor capable of selectively stimulating respiratory processes relevant to the bioremediation of perchlorate. Pure cultures of Dechloromonas aromatica, Dechloromonas agitata and Azospira suillum, as well as uncharacterized microbial consortia, were capable of stoichiometrically reducing perchlorate to chloride upon oxidation of AH 2 DS to the corresponding quinone 2,6-anthraquinone disulfonate (AQDS). No degradation of the anthraquinone structure was observed, and no organism tested grew by this metabolism. Thermodynamic calculations suggest that AH 2 DS oxidation should support nitrate and perchlorate reduction, whereas sulfate reduction and methanogenesis are predicted to be unfavorable. Mixed community microcosms oxidizing AH 2 DS reduced nitrate and perchlorate, whereas sulfate reduction never occurred. In contrast, microcosms amended with acetate respired nitrate, perchlorate and sulfate, as would be predicted by thermodynamic calculation. Our results suggest that the thermodynamic properties of hydroquinones allow for targeted stimulation of only a subset of potential respiratory processes. This observation could help improve enhanced in situ bioremediation of perchlorate by negating many of the detrimental aspects of biofouling.

Impacts of Poultry House Environment on Poultry Litter Bacterial Community Composition

“…This genus is of interest due to its potential for use in bioremediation. Strains of Azospira have been isolated that are able to reduce selenate and selenite to elemental selenium [59], and reduce the perchlorate to chloride [60]. Perchlorate reducing bacteria (putative Azospira sp and Dechloromonas sp) have been found in numerous soil and sediment environments [57] but this is the first study to report the presence of genus Azospira in a litter environment.…”

Humic Acid-Oxidizing, Nitrate-Reducing Bacteria in Agricultural Soils

“…AH 2 DS and reduced humic acid concentrations were analyzed by ferric citrate back-titration or spectrophotometrically as previously described (21, 39, 40). Total anthraquinone concentrations were determined by aerating filtered samples and quantifying AQDS as previously described (29). Fe(II) was quantified with a ferrozine assay as previously described (46).…”

“…However, reduced redox-active functional groups within HA can be readily oxidized as electron donors for bacterial respiration (20, 21). The hydroquinone content of reduced HA are considered important humus-borne electron donors of this type, and microbial oxidation of hydroquinones to corresponding quinones has been demonstrated to support nitrate, perchlorate, arsenate, and selenate reduction (20, 21, 27–29). Microbial hydroquinone oxidation has been most clearly demonstrated with the model compound 2,6-anthrahydroquinone disulfonate (AH 2 DS), which can be oxidized to its quinone form 2,6-anthraquinone disulfonate (AQDS).…”

Transposon and Deletion Mutagenesis of Genes Involved in Perchlorate Reduction in Azospira suillum PS

“…It grows rapidly and robustly on rich media, and its genome has been fully sequenced and is publicly available (11, 19). Additionally, its perchlorate-reducing physiology has been studied in the context of environmental regulation (13), chemotaxis (20), and redox cycling of electron shuttles (21, 22). …”