Role of Redox Shuttles in the Biotransformation of Insensitive Munition Compounds by Geobacter

Abstract

3-Nitro-1,2,4-triazol-5-one (NTO) is a nitroheterocyclic compound that is a component of insensitive explosives. Due to the lower risk of accidental detonation, insensitive munitions are being used more frequently in place of conventional explosives. Environmental contamination with insensitive munition compounds (IMCs) occurs from industrial wastewater discharge and undetonated material in soil. The toxicity of NTO is not fully understood and has created a need to remove it from the environment. Prior research has developed a highly enriched culture for NTO bioreduction. This culture, composed mainly of Geobacter anodireducens and Thauera species, reduces NTO to 3-amino-1,2,4-triazol-5-one (ATO) and oxidizes acetate to CO2. This study explores the possibility of using redox mediators to increase the rate of NTO reduction or to expand the range of compounds that could be reduced by the culture. The redox mediator chosen for these experiments is 9,10-anthraquinone-2,6-disulfonate (AQDS), a model compound for other humic substances present in soil. It was found that the addition of AQDS to the enrichment culture with NTO can increase the rate of NTO reduction. The AQDS was directly reduced to 9,10-anthrahydroquinone-2,6-disulfonate (AH2QDS) by the enrichment culture with acetate as an electron donor. The reduced quinone can chemically react with NTO and other nitro group containing compounds to reduce the nitro compounds while oxidizing back into AQDS. This study highlights the potential of increased NTO reduction rates with redox mediators and the potential to expand the substrate spectrum of what can be reduced by this enrichment culture.