Review Article | Published:

Microbial perchlorate reduction: rocket-fuelled metabolism

Nature Reviews Microbiology volume 2, pages 569580 (2004) | Download Citation

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Abstract

It is less than 7 years since perchlorate, a predominantly man-made toxic anion, was first identified as a significant water contaminant throughout the United States. Owing to its solubility and non-reactivity, bioremediation was targeted as the most promising solution for the problem of perchlorate contamination. Since 1996, concerted efforts have resulted in significant advances in our understanding of the microbiology, biochemistry and genetics of the microorganisms that are capable of reductively transforming perchlorate into innocuous chloride. The recent completion of the whole-genome sequence of the perchlorate-reducing microorganism Dechloromonas aromatica offers further insight into the evolution and regulation of this unique metabolic pathway. Several in situ and ex situ bioremediative processes have been engineered, and many monitoring tools that are based on immunology, molecular biology and stable isotope content are now available. As such, the rapid scientific response to this emerging contaminant offers great hope for its successful elimination from contaminated environments in the future.

Key points

  • Perchlorate (ClO4) is a soluble anion that comprises a central chlorine atom surrounded by four oxygen atoms. In the United States, perchlorate contamination of drinking water supplies is currently an issue of great public concern.

  • Perchlorate is principally a man-made compound and its presence as an environmental contaminant mainly results from the use of ammonium perchlorate in the munitions industry as an energetics booster or oxidant in solid rocket fuels. Owing to its chemical stability and high solubility, perchlorate is an excellent candidate for microbial-mediated bioremediation.

  • Dissimilatory (per)chlorate-reducing bacteria (DPRB) can grow by the anaerobic reductive dissimilation of (per)chlorate — perchlorate and chlorate (ClO3) — into chloride. More than 50 DPRB species are now in pure culture. These microorganisms have been identified in a wide range of environments and have a broad range of metabolic capabilities. They are phylogenetically diverse, with members in the α-, β-, γ- and ε-Proteobacteria. Two novel genera in the β-Proteobacteria, Dechloromonas and Azospira, are thought to be the dominant (per)chlorate-reducing bacteria in the environment.

  • Recent studies have yielded important data on the physiology, biochemistry and genetics of microbial (per)chlorate reduction. Additionally, information is now available on the environmental factors that influence the activity of DPRB. With these data to hand, new in situ and ex situ bioremediation strategies can be developed. The progress of these strategies can also now be monitored using the unique signature molecules and novel metabolic capabilities of the DPRB, including immunoprobes specific for chlorite dismutase and stable isotope analysis. The recent completion of the draft genome sequence of the (per)chlorate-reducing organism Dechloromonas aromatica strain RCB promises further advances in microbial perchlorate reduction.

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Acknowledgements

Research on the microbial reduction of perchlorate and application of these microorganisms to the bioremediation of perchlorate, heavy metals, radionucleotides and hydrocarbons in the laboratories of J.D.C. and L.A.A. is supported by independent grants from the US Department of Defence SERDP program and the US Department of Energy NABIR program.

Author information

Affiliations

  1. Department of Plant and Microbial Biology, 271 Koshland Hall, University of California, Berkeley, California 94720, USA.

    • John D. Coates
  2. Department of Microbiology, Southern Illinois University, Carbondale, Illinois 62901, USA.

    • Laurie A. Achenbach

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Competing interests

The authors declare no competing financial interests.

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Correspondence to John D. Coates.

Glossary

HYPOTHYROIDISM

The most common thyroid disorder and one in which the thyroid is underactive.

PROVISIONAL ACTION LEVEL

A contamination level set by each state in the United States that is used to protect consumers until a federal maxiumium concentration level is defined by the US EPA.

CONTAMINANT CANDIDATE LIST

The primary source of priority contaminants for evaluation by the EPA's drinking water programme; updated every five years.

HYDROPONIC GROWTH

Growing plants in water containing dissolved nutrients instead of soil.

REVERSE OSMOSIS

A process in which purified water is obtained from a salt solution.

MAGNETOTACTIC

Magnetotactic bacteria are motile, mostly aquatic prokaryotes that can swim along geomagnetic field lines.

MAGNETOSOMES

Intracellular structures in magnetotactic bacteria that contain magnetic mineral crystals.

SLOT-BLOT

A technique that is used to determine whether an organism possesses a specific gene of interest. Genomic DNA is extracted and transferred to a solid membrane with a slot-array apparatus. After denaturation of the DNA, the membrane is hybridized with a labelled probe that targets a specific DNA sequence.

CLADE

A group of organisms consisting of a single species and its descendents.

MOST PROBABLE NUMBER

A method that uses dilution cultures to determine the approximate number of viable cells. It is useful when samples contain too few organisms for agar plates to be used or when organisms will not grow on agar.

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https://doi.org/10.1038/nrmicro926

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