Ubiquity and Diversity of Dissimilatory (Per)chlorate-Reducing Bacteria

Abstract

Environmental contamination with compounds containing oxyanions of chlorine, such as perchlorate or chlorate [(per)chlorate] or chlorine dioxide, has been a constantly growing problem over the last 100 years. Although the fact that microbes reduce these compounds has been recognized for more than 50 years, only six organisms which can obtain energy for growth by this metabolic process have been described. As part of a study to investigate the diversity and ubiquity of microorganisms involved in the microbial reduction of (per)chlorate, we enumerated the (per)chlorate-reducing bacteria (ClRB) in very diverse environments, including pristine and hydrocarbon-contaminated soils, aquatic sediments, paper mill waste sludges, and farm animal waste lagoons. In all of the environments tested, the acetate-oxidizing ClRB represented a significant population, whose size ranged from 2.31 × 103 to 2.4 × 106 cells per g of sample. In addition, we isolated 13 ClRB from these environments. All of these organisms could grow anaerobically by coupling complete oxidation of acetate to reduction of (per)chlorate. Chloride was the sole end product of this reductive metabolism. All of the isolates could also use oxygen as a sole electron acceptor, and most, but not all, could use nitrate. The alternative electron donors included simple volatile fatty acids, such as propionate, butyrate, or valerate, as well as simple organic acids, such as lactate or pyruvate. Oxidized-minus-reduced difference spectra of washed whole-cell suspensions of the isolates had absorbance maxima close to 425, 525, and 550 nm, which are characteristic of type c cytochromes. In addition, washed cell suspensions of all of the ClRB isolates could dismutate chlorite, an intermediate in the reductive metabolism of (per)chlorate, into chloride and molecular oxygen. Chlorite dismutation was a result of the activity of a single enzyme which in pure form had a specific activity of approximately 1,928 μmol of chlorite per mg of protein per min. Analyses of the 16S ribosomal DNA sequences of the organisms indicated that they all belonged to the alpha, beta, or gamma subclass of the Proteobacteria. Several were closely related to members of previously described genera that are not recognized for the ability to reduce (per)chlorate, such as the generaPseudomonas and Azospirllum. However, many were not closely related to any previously described organism and represented new genera within the Proteobacteria. The results of this study significantly increase the limited number of microbial isolates that are known to be capable of dissimilatory (per)chlorate reduction and demonstrate the hitherto unrecognized phylogenetic diversity and ubiquity of the microorganisms that exhibit this type of metabolism.

Identification of acetate‐utilizing Bacteria and Archaea in methanogenic profundal sediments of Lake Kinneret (Israel) by stable isotope probing of rRNA

“…Electron acceptors that are frequently found in anoxic soils and sediments, such as nitrate, manganese, iron, sulfate, were absent or too low in concentration to serve as electron acceptors in our experiments with Lake Kinneret sediment. Still, we have to state that other possible oxidants, including chlorinated aliphatic and aromatic compounds or (per)chlorate (Holliger et al, 1998;Coates et al, 1999) and humic compounds (Lovley et al, 1996) remain likely candidates of explanation.…”

Perchlorate reduction in a HYDROGEN‐BASED MEMBRANE–BIOFILM REACTOR

“…Longitudinal cross-section of a hollow fiber reductase (Kengen et al, 1999) and chlorite dismutase (van Ginkel et al, 1996) suggest that the perchlorate reduction is rate-limiting; thus, chlorate and chlorite should not accumulate. Known PCRB include members of the ␣-, ␤-, ␥-, ␦-, and ⑀-subclasses of the Proteobacteria (Achenbach et al, 2001;Coates et al, 1999;Wallace et al, 1996). Many known PCRB appear to be within two genera of the ␤-Proteobacteria named Dechloromonas and Dechlorosoma (Achenbach et al, 2001;Logan et al, 2001).…”

Novel biomarkers of perchlorate exposure in zebrafish

“…Compounds containing oxyanions of chlorine, such as perchlorate, chlorate, or chlorine dioxide, are of growing concern as environmental contaminants [1]. Perchlorate has been used for more than 50 years in the manufacture of ammunitions, missiles, and matchsticks; in industries such as leather processing, electroplating, aluminum refining, rubber manufacture, and paints and enamel production [2] (http:// www.epa.gov/safewater/ccl/perchlorate/pdf/r9699fac.pdf); and in fertilizers [3].…”