Thermodynamic targeting of microbial perchlorate reduction by selective electron donors

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.