Ammonium perchlorate is used as an oxidizer component in solid propellant (fuel) for rockets, missiles, and fireworks. The high solubility of ammonium perchlorate coupled with its chemical stability in water leads to expansive plumes. Robust abiotic or biotic in-situ methods for treating large volumes of groundwater contaminated with perchlorate in the presence of co-contaminants are needed. The objective of this project was to gain a better understanding of the microbiology involved in microbial perchlorate reduction with an aim of enhancing the application of this novel metabolism to the attenuation of perchlorate-contaminated environments.

Perchlorate-reducing bacteria can reduce perchlorate completely to innocuous chloride and gain energy for growth by this metabolism

This project provided a better understanding of the microbiology involved in microbial perchlorate reduction and removal. The factors controlling the applicability of these microorganisms to the in-situ treatment of ammonium perchlorate contamination of natural water supplies also were determined. In addition, this work assisted in the development of protocols and molecular tools required for the modeling and application of in-situ bioremediation strategies to treat perchlorate contamination.

This project demonstrated the ubiquity of microbial perchlorate reduction and the diversity of microorganisms capable of dissimilatory perchlorate reduction. Researchers identified the dominant perchlorate-reducing bacteria and factors controlling their activity in the environment. The ability of these organisms to alter the chloride and oxygen stable isotope ratios of perchlorate was demonstrated. Theprimary enzymes involved in metabolism were purified, and the genetics of microbial perchlorate reduction were identified. The highly conserved nature of the enzymes and genes involved in metabolism suggested horizontal gene transfer. Using this information, researchers developed a highly specific universal immunoprobe and highly sensitive specific molecular gene probes for perchlorate reducing bacteria. Overall, these studies have resulted in numerous articles in the popular press, radio and television interviews, publications in peer-reviewed journals, and patent applications.

Results from these studies have provided a better understanding of the microbiology involved in perchlorate reduction and the factors controlling the activity of these organisms. These studies also allowed for the development of a molecular probe that is specific for all perchloratereducing bacteria. Such a probe has been used for predictive determinations of the success of a biological in-situ treatment process and also as a monitoring tool for intrinsic or enhanced bioremediative efforts. Many of the discoveries of this project are responsible for the successful implementation of perchlorate bioremediation technologies, and several of the tools developed are currently in commercial application. (Project Completed – 2006)