JOURNAL OF BACTERIOLOGY, Aug. 2005, p. 5090–5096
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Vol. 187, No. 15
Identification, Characterization, and Classification of Genes Encoding
Kelly S. Bender,1† Ching Shang,2Romy Chakraborty,2Sara M. Belchik,1John D. Coates,2
and Laurie A. Achenbach1*
Department of Microbiology, Southern Illinois University, Carbondale, Illinois 62901,1and Department of Plant and Microbial
Biology, University of California Berkeley, Berkeley, California 945982
Received 3 March 2005/Accepted 25 April 2005
The reduction of perchlorate to chlorite, the first enzymatic step in the bacterial reduction of perchlorate, is
catalyzed by perchlorate reductase. The genes encoding perchlorate reductase (pcrABCD) in two Dechloromonas
species were characterized. Sequence analysis of the pcrAB gene products revealed similarity to ?- and
?-subunits of microbial nitrate reductase, selenate reductase, dimethyl sulfide dehydrogenase, ethylbenzene
dehydrogenase, and chlorate reductase, all of which are type II members of the microbial dimethyl sulfoxide
(DMSO) reductase family. The pcrC gene product was similar to a c-type cytochrome, while the pcrD gene
product exhibited similarity to molybdenum chaperone proteins of the DMSO reductase family members
mentioned above. Expression analysis of the pcrA gene from Dechloromonas agitata indicated that transcription
occurred only under anaerobic (per)chlorate-reducing conditions. The presence of oxygen completely inhibited
pcrA expression regardless of the presence of perchlorate, chlorate, or nitrate. Deletion of the pcrA gene in
Dechloromonas aromatica abolished growth in both perchlorate and chlorate but not growth in nitrate, indi-
cating that the pcrABCD genes play a functional role in perchlorate reduction separate from nitrate reduction.
Phylogenetic analysis of PcrA and other ?-subunits of the DMSO reductase family indicated that perchlorate
reductase forms a monophyletic group separate from chlorate reductase of Ideonella dechloratans. The sepa-
ration of perchlorate reductase as an activity distinct from chlorate reductase was further supported by DNA
hybridization analysis of (per)chlorate- and chlorate-reducing strains using the pcrA gene as a probe.
Ammonium perchlorate (NH4ClO4), a common component
of solid rocket fuel, is a widespread environmental contami-
nant in water systems in the United States (9, 25). While
attempts at implementing regulatory standards have created
discord between the Environmental Protection Agency and
other federal agencies (9, 26), perchlorate remains a health
issue due to its effects on the thyroid gland (34). Based on the
chemical properties of perchlorate, remediation efforts have
focused primarily on dissimilatory perchlorate-reducing bacte-
ria (DPRB). Despite the isolation of over 50 perchlorate-re-
ducing strains (6, 8–10, 33), our knowledge of the metabolic
pathway involved is rudimentary.
Chlorite dismutase and perchlorate reductase are the only
enzymes in the perchlorate reduction pathway that have been
isolated and characterized (10, 16, 23, 32), and molecular data
are available only for chlorite dismutase (2, 11). The first step
in microbial perchlorate reduction is the reduction of perchlor-
enzyme. To date, data are available for purified perchlorate
reductase from two perchlorate-reducing bacteria, strains
GR-1 and perc1ace (16, 23). The GR-1 analysis revealed an
oxygen-sensitive periplasmic enzyme that resembled known
nitrate and selenate reductases in both subunit and metal com-
position. Iron, molybdenum, and selenium were the metal con-
stituents of this heterodimeric (?3?3) perchlorate reductase
?) to chlorite (ClO2
?) by the perchlorate reductase
that was capable of reducing both perchlorate and chlorate to
chlorite (16). Similarly, the perchlorate reductase from
perc1ace (23) was composed of two subunits, and tryptic pep-
tides obtained from the small subunit exhibited amino acid
similarities to reductases, dehydrogenases, and heme proteins.
Although the perc1ace tryptic peptide sequences and the N-
terminal amino acid sequence of the ?-subunit of the GR-1
perchlorate reductase have been reported (14, 20), the genes
encoding this enzyme were not identified for either organism.
While genes encoding a chlorate reductase operon were
recently reported for the chlorate-reducing organism Ideonella
dechloratans (12, 35), this enzyme was unable to reduce envi-
ronmentally significant perchlorate. Furthermore, although
microbial nitrate reductases also recognize chlorate as a sub-
strate, it is not known whether perchlorate is similarly recog-
nized (30). Even so, growth of dissimilatory nitrate-reducing
bacteria cannot be sustained from the gratuitous reduction of
chlorate or perchlorate unless some biochemical mechanism,
such as chlorite dismutation (10), is present to alleviate the
accumulation of toxic chlorite (30). Here we report the first
identification and characterization of the genes encoding per-
chlorate reductase, the distribution of this enzyme among phy-
logenetically diverse perchlorate-reducing bacteria, and classi-
fication of perchlorate reductase as a member of the microbial
dimethyl sulfoxide (DMSO) reductase family of molybdenum
MATERIALS AND METHODS
Growth conditions. Dechloromonas agitata and Dechloromonas aromatica
were grown both anaerobically and aerobically in basal media as previously
described (2, 6). For anaerobic cultures, 10 mM acetate and 10 mM perchlorate,
chlorate, or nitrate were used as the electron donor and the electron acceptor,
* Corresponding author. Mailing address: Department of Microbi-
ology, Southern Illinois University, Carbondale, IL 62901. Phone:
(618) 453-7984. Fax: (618) 453-8036. E-mail: email@example.com.
† Present address: Department of Biochemistry, University of Mis-
souri-Columbia, Columbia, MO 65211.
respectively. For aerobic growth, (per)chlorate was omitted and oxygen was
added to the same basal media. To check for induction under aerobic conditions,
1 mM sodium nitrate, chlorate, or perchlorate was added to aerobically grown
Nucleic acid extraction and mutant construction. Both genomic DNA and
RNA were extracted as previously described using a PUREGENE DNA isola-
tion kit (Gentra Systems Inc., Minneapolis, MN) and the RNAwiz reagent
(Ambion, Austin, TX), respectively (2). A pcrA mutant of D. aromatica was
constructed by replacement of the pcrA gene with a tetracycline resistance cas-
sette as previously described (29). Briefly, a region upstream of the pcrA start
codon and a region downstream of the pcrA stop codon were PCR amplified and
inserted on either side of a 1.6-kb pBR322 tetracycline resistance cassette that
had been cloned into a suicide vector. This construct was used to transform D.
aromatica cells; double-recombination mutants in which the pcrA gene on the
chromosome had been replaced with the resistance cassette were verified by
Sequence analysis. DNA sequences obtained from D. agitata lambda library
screening (2), as well as the complete genome sequence of D. aromatica, ob-
tained courtesy of the Joint Genome Institute (http://www.jgi.doe.gov), were
subjected to BLAST analysis (1). DNA sequence manipulations were performed
using the MacVector sequence analysis software for the Macintosh (version 7.0;
Oxford Molecular) and the Se-Al sequence alignment editor, v. 1.0 (A. Rambaut,
University of Oxford).
Hybridization analyses. Northern blotting was performed using the Northern-
Max-Gly glyoxal-based system (Ambion) as previously described (2). For all
growth conditions, 5 ?g of total RNA was loaded onto a 1% (wt/vol) glyoxal
agarose gel. Following RNA transfer, the blot was hybridized at 50°C in Easyhyb
hybridiztion solution (Roche Applied Science, Indianapolis, IN) with a digoxi-
genin-labeled probe corresponding to 436 bp in the 5? half of the D. agitata pcrA
gene. This probe was generated via PCR at an annealing temperature of 55°C
with the following primers: PR-750F (5?-CGCGAAGGTAGTCAGCATCT-3?)
and PR-1185R (5?-TCCATCCTGCAACTTGACCT-3?). For DNA slot blotting,
genomic DNAs from known DPRB and non-perchlorate-reducing close relatives
were blotted as previously described (2). The blot was hybridized at 45°C with the
same perchlorate reductase probe used in the Northern blot analysis.
Phylogenetic analysis. Protein sequences from the ?-subunits of known
DMSO reductase enzymes were obtained from the GenBank database (3) and
aligned with the ?-subunit of perchlorate reductase using the CLUSTALW 1.82
program (31). A phylogenetic tree was constructed with the PAUP? v 4.0 pro-
gram (D. L. Swofford, Sinauer Associates) using distance as the criterion and
neighbor joining as the drawing method.
GenBank accession numbers. The GenBank accession numbers for the D.
agitata perchlorate reductase genes are as follows: pcrA, AY180108; pcrB,
AY953269; pcrC, AY953270; and pcrD, AY953271. The accession numbers for
the protein sequences shown in Fig. 2 are as follows: SerB, Q9S1G9; ClrB,
P60069; EbdB, CAD58340; DdhB, AAN46633; and NarH, CAD22070. The
accession number for the Nitrosomonas europaea cytochrome c554shown in Fig.
3 is NP_842334. The GenBank accession numbers for the 16S rRNA gene
sequences of the organisms shown in Fig. 7 are as follows: D. agitata, AF047462;
Rhodocyclus tenuis, D16209; D. aromatica, AY032610; Dechloromonas sp. strain
JJ, AY032611; Dechlorospirillum anomolous strain WD, AF170352; Magnetospi-
rillum magnetotacticum, Y10110; Pseudomonas sp. strain PK, AF170358; Pseudo-
monas stutzeri, U26415; Dechloromarinus chlorophilus strain NSS, AF170359;
Azospira suillum, AF170348; Dechloromonas sp. strain LT-1, AY124797; and I.
FIG. 1. Diagram of the pcrABCD genes of D. agitata and D. aromatica. The N-terminal sequences of PcrA are indicated, and the twin-arginine
motif is in boldface type.
TABLE 1. BLAST analysis of the pcrABCD translation products
Gene GenBank BLAST hit
pcrA CAD22069, Haloarcula marismortui nitrate reductase ?-subunit (NarG)
CAF21906, Haloferax mediterranei nitrate reductase ?-subunit (NarG)
AAN46632, Rhodovulum sulfidophilum dimethyl sulfide dehydrogenase ?-subunit (DdhA)
Q9S1H0, Thauera selenatis selenate reductase ?-subunit (SerA)
P60068, Ideonella dechloratans chlorate reductase ?-subunit (ClrA)
pcrBQ9S1G9, Thauera selenatis selenate reductase ?-subunit (SerB)
P60069, Ideonella dechloratans chlorate reductase ?-subunit (ClrB)
CAD58340, Azoarcus sp. strain EbN1 ethylbenzene dehydrogenase ?-subunit (EbdB)
AAN46633, Rhodovulum sulfidophilum dimethyl sulfide dehydrogenase ?-subunit (DdhB)
pcrCNP_842334, Nitrosomonas europaea cytochrome c554precursor
pcrDQ9S1G8, Thauera selenatis selenate reductase (SerD)
AAN46634, Rhodovulum sulfidophilum dimethyl sulfide dehydrogenase ?-subunit (DdhD)
CAD58338, Azoarcus sp. strain EbN1 ethylbenzene dehydrogenase ?-subunit (EbdD)
CAD22073, Haloarcula marismortui nitrate reductase molybdenum chaperone (NarJ)
VOL. 187, 2005PERCHLORATE REDUCTASE GENES5091
RESULTS AND DISCUSSION
Identification of pcrABCD genes. In the course of character-
izing the chlorite dismutase (cld) gene (2), we identified a
proximal operon putatively encoding perchlorate reductase in
the genomes of two DPRB, D. agitata and D. aromatica. The
orientation of the perchlorate reductase genes was the same in
both DPRB with exception of the position of the cld gene (Fig.
1). BLAST analysis of the open reading frames, designated
pcrABCD, revealed amino acid similarities to subunits of mi-
crobial nitrate reductase, selenate reductase (serABDC), di-
methyl sulfide dehydrogenase (ddhABDC), ethylbenzene de-
hydrogenase (ebdABCD), and chlorate reductase (clrABDC),
all of which are members of the type II DMSO reductase
family (Table 1). While the serABDC (16), ddhABDC (17), and
clrABDC (12) operons all have the same gene order, the
pcrABCD operon mimics the ebdABCD (21) operon arrange-
ment. The significance of this observation is not known.
pcrA. Translational analysis of the 2,784-bp pcrA gene iden-
tified a molybdopterin-binding domain (data not shown), as
well as a twin-arginine signal motif, (S/T)RRXFLK (Fig. 1).
FIG. 2. Amino acid alignment of the ?-subunit of perchlorate reductases (PcrB) from strain GR-1 (St.GR1) (N-terminal sequence only), D.
agitata (D.agit), and D. aromatica (D.arom), selenate reductase B (SerB) from T. selenatis (T.sele), chlorate reductase (ClrB) from I. dechloratans
(I.dech), ethylbenzene dehydrogenase B (EbdB) from Azoarcus sp. strain EbN1 (A.EbN1), dimethyl sulfide dehydrogenase B (DdhB) from R.
sulfidophilum (R.sulf), and nitrate reductase H (NarH) from H. marismortui (H.mars). Light shading indicates amino acids identical to amino acids
in both perchlorate reductases. Dark shading indicates conserved cysteine clusters for Fe-S center binding. The numbers below the cysteine
residues indicate the associated Fe-S centers.
FIG. 3. Amino acid alignment of the ?-subunit of perchlorate reductase (PcrC) from D. aromatica (D.arom) and cytochrome c554from N.
europaea (N.euro). Shading indicates identical residues, while boldface and underlining indicate residues shown to bind heme in cytochrome c554
5092BENDER ET AL. J. BACTERIOL.
Previous studies have suggested that the twin-arginine motif
tags proteins involved in electron transfer reactions, whose
prosthetic groups are formed in the cytoplasm prior to secre-
tion, for transport to the periplasm via Sec-independent trans-
port (Tat pathway) (5). This motif is also commonly found in
electron transfer proteins possessing a pterin molybdenum co-
factor and iron-sulfur (Fe-S) centers (4). Since the perchlorate
reductase of GR-1 was located in the periplasm and contained
molybdenum and Fe-S centers (16), the presence of this signal
peptide further supports identification of the pcrA gene as the
gene encoding the ?-subunit of the perchlorate reductase. In
addition, the calculated molecular mass of the PcrA subunit is
105 kDa, a value that corresponds well to the 95 kDa predicted
for the ?-subunit of the purified perchlorate reductase from
pcrB. The inferred amino acid sequence of the 1,002-bp pcrB
gene product indicated the presence of four cysteine-rich clus-
ters for Fe-S center binding, a feature shared with ?-subunits
of type II DMSO reductase enzymes (Fig. 2). This cysteine
organization has been shown to bind one 3Fe-4S center and
three 4Fe-4S centers in both dimethyl sulfide dehydrogenase
(19) and nitrate reductase (15) ?-subunits. Based on data for
the ?-subunit of the Escherichia coli nitrate reductase (13),
these Fe-S centers may be responsible for electron transfer to
the molybdopterin-containing ?-subunit of perchlorate reduc-
The predicted N-terminal amino acid sequences of the D.
agitata and D. aromatica PcrB proteins were aligned with the
N-terminal sequence of purified PcrB from GR-1 (16). This
alignment reinforced the identity of the pcrB gene (Fig. 2). The
predicted D. agitata PcrB N terminus contained 10 of the 18
residues and the predicted D. aromatica PcrB sequence con-
tained 16 of the 18 residues reported for the purified perchlor-
ate reductase ?-subunit from strain GR-1. Since no signal
sequence was detected, the ?-subunit of perchlorate reductase
is likely translocated with the ?-subunit in a manner similar to
that proposed for selenate reductase (18), dimethyl sulfide
dehydrogenase (20), and chlorate reductase (12). The calcu-
lated molecular mass of the PcrB subunit was 37 kDa, a value
similar to the 40 kDa reported for the ?-subunit of the purified
perchlorate reductase from GR-1 (16).
pcrC. Although a ?-subunit was not detected in the enzyme
analysis of the perchlorate reductase from strain GR-1, a third
cytochrome-type subunit responsible for connecting the reduc-
tase to the membrane was believed to have been lost during
purification of the enzyme (16). This observation was borne
out by our identification of a 711-bp open reading frame im-
mediately downstream of the pcrB gene in both D. aromatica
and D. agitata, whose product exhibited sequence similarity to
cytochrome c554from N. europaea (Table 1). Amino acid align-
ment indicated that PcrC also has the unique tetraheme orga-
nization of cytochrome c554from N. europaea (14) (Fig. 3). The
lack of amino acid sequence similarity between PcrC (ca. 25
kDa) and other type II DMSO reductase ?-subunits was not
surprising due to the overall sequence diversity noted in the
SerC, EbdC, DhdC, and ClrC subunits (12).
The ProteinPredict server (http://cubic.bioc.columbia.edu
/pp/) indicated that the pcrC translation product is not a mem-
brane-bound protein and therefore cannot link the PcrAB
complex to the membrane. However, further analysis of the D.
aromatica genome revealed the presence of a NirT-type cyto-
chrome gene downstream of the chlorite dismutase gene. The
cytochrome may link the periplasmic PcrABC reductase to the
FIG. 4. Predicted model for electron transfer during (per)chlorate
reduction. Electrons from a quinone pool are transferred from the
membrane via a NirT-type cytochrome to the PcrABC reductase.
While PcrD is absent from the functional enzyme, this protein is
predicted to be involved in enzyme assembly.
FIG. 5. Anaerobic growth of wild-type D. aromatica and pcrA mu-
tant with nitrate (a), perchlorate (b), or chlorate (c) as the sole elec-
tron acceptor. F, wild-type growth; E, pcrA mutant growth. The data
are averages for duplicate incubations.
VOL. 187, 2005PERCHLORATE REDUCTASE GENES 5093
membrane quinol pool (Fig. 4). Membrane-bound NirT-type
cytochromes have been shown to shuttle electrons to the
periplasmic nitric reductase of P. stutzeri, the Fe3?and fuma-
rate reductases of Shewanella putrefaciens, and the periplasmic
nitrate reductase (21, 27, 28). The model predicted for per-
chlorate reduction (Fig. 4) differs from the model projected for
selenate reduction (21) by replacement of the bc1complex with
a NirT-type cytochrome.
pcrD. Based on sequence identity with SerD, DdhD, EbdD,
and NarJ, the final 675-bp pcrD gene likely encodes a system-
specific molybdenum chaperone protein (ca. 25 kDa) (Table
1). This finding is supported by the absolute requirement for
molybdenum for active perchlorate reduction (7). The SerD,
DdhD, and EbdD proteins are believed to be involved in as-
sembly of the mature molybdenum-containing selenate reduc-
tase, dimethyl sulfide dehydrogenase, and ethylbenzene dehy-
drogenase, respectively, prior to periplasmic translocation via
the Tat pathway. However, these proteins are not believed to
be parts of the active enzymes (18, 20, 24).
Expression and mutagenesis of pcrA. Both expression anal-
ysis and mutagenesis of the pcrA gene verified the identity of
the pcrABCD operon. Northern analysis of D. agitata RNA
indicated that there was pcrA gene expression in anaerobic
perchlorate- and chlorate-grown cultures (data not shown).
However, the presence of perchlorate, chlorate, or nitrate was
not enough to induce pcrA expression in aerobic cultures and,
as such, indicates the ability of oxygen to completely inhibit
pcrA expression, as suggested by the previously documented
inhibitory effects of oxygen on perchlorate reduction (7, 22).
Functional proof that the pcrA gene is involved in perchlor-
ate reduction was obtained by mutational knockout in D. aro-
matica, in which insertional inactivation of the pcrA gene with
a tetracycline resistance cassette abolished both perchlorate
and chlorate reduction (Fig. 5). However, as expected, the D.
aromatica pcrA mutant was still able to grow aerobically (data
not shown), as well as anaerobically via nitrate reduction, in-
dicating that there are separate metabolic pathways for each
electron acceptor (Fig. 5).
Phylogenetic analysis of PcrA. Based on the biochemical
analysis of the purified enzyme from strain GR-1 (16), per-
chlorate reductase was identified as a member of the type II
DMSO reductase family (21). Our sequence analysis of the
perchlorate reductase genes also supported this identification.
Enzymes in the prokaryotic type II DMSO reductase family
reside in the periplasm and have a common pterin molybde-
num cofactor known as bis(molybdopterin guanine dinucleo-
tide)Mo (17, 20, 21). DMSO reductase enzymes are involved in
a myriad of reduction capabilities, including the dissimilatory
reduction of toxic elements such as selenate and arsenate (21).
Using ?-subunit protein sequences from known microbial
DMSO enzymes (20, 21) and from the PcrA sequences result-
ing from this study, a phylogenetic tree was constructed (Fig.
6), and this tree had a topology similar to that of a DMSO
FIG. 6. Unrooted neighbor-joining tree indicating the evolutionary distances in the DMSO reductase family of molybdoenzymes. GenBank
accession numbers are indicated after the names.
5094 BENDER ET AL.J. BACTERIOL.
reductase family tree constructed by McEwan and coworkers
The type I, type II, and type III DMSO enzymes form sep-
arate clades in the tree. The type I enzymes include formate
dehydrogenase (FDH), periplasmic nitrate reductase (NapA),
bacterial assimilatory nitrate reductase (NasA), and arsenite
oxidase (AsoA) (20, 21). Type II enzymes, such as ethylben-
zene dehydrogenase (EbdA), dimethyl sulfide dehydrogenase
(DdhA), selenate reductase (SerA), chlorate reductase (ClrA),
nitrate reductase (NarG), and perchlorate reductase (PcrA),
share a heterotrimeric structure and have conserved cysteine
residues for Fe-S binding in the ?-subunit (20, 21). The type III
enzymes are represented by the monomeric proteins biotin
sulfoxide reductase (BisC), dimethyl sulfoxide reductase
(DorA), and trimethylamine-N-oxide reductase (TorA) (20,
21). The type II enzyme dimethyl sulfoxide reductase (DmsA)
and the type II enzymes polysulfide and thiosulfate reductases
(PsrA/PhsA) form unaffiliated lineages (20, 21).
Our analysis indicated that PcrA forms its own monophyletic
group in the type II DMSO enzymes and has a common an-
cestor with E. coli and Bacillus subtilis NarG, I. dechloratans
ClrA, Thauera selenatis SerA, Rhodovulum sulfidophilum
DdhA, and Azoarcus sp. strain EB1 EbdA. The alignment used
for tree construction indicated that PcrA contains the type II
DMSO signature motif [HX3CX2CX(n)C] for binding one
4Fe-4S center in domain I (data not shown) (15). Based on the
NarG analysis of Jormakka and coworkers, type II DMSO
enzymes have also been shown to contain a conserved Asp
residue for Mo ion binding (15). This residue is present at
position 212 in PcrA.
The tree topology also indicated that PcrA is more closely
related to NarG from B. subtilis and E. coli than to ClrA from
I. dechloratans, further emphasizing the differences between
the perchlorate and chlorate reductases. The distance between
the perchlorate and chlorate reductases indicates that they are
distinct enzymes, which was supported by our molecular prob-
ing of genomic DNAs from perchlorate and chlorate reducers,
as well as from close relatives unable to reduce either electron
acceptor (Fig. 7). The slot blot analysis resulted in hybridiza-
tion signals for the pcrA gene from perchlorate reducers alone.
No signal was observed for the close relatives or for Pseudo-
monas sp. strain PK, D. chlorophilus, or I. dechloratans, organ-
isms that are capable of chlorate reduction but not perchlorate
reduction (Fig. 7). This finding supports the hypothesis that
two distinct metabolic pathways involved in the reduction of
these analogous compounds evolved.
From the current study, it is clear that a more complete
understanding of perchlorate reduction and other environmen-
tally significant pathways is pivotal for obtaining knowledge
applicable to the design of future bioremediation strategies.
Perchlorate reductase and other members of the type II
DMSO reductase family play a role in a broad range of sub-
strate reductions and oxidations, and differences in various
active sites are the major differences between family members.
The different active sites indicate that there was a common
reductase ancestor which acquired mutations advantageous for
utilization of specific substrates. Thus, it is possible that di-
rected mutagenesis of the active sites of DMSO enzymes could
lead to creation of novel enzymes useful for biotechnological
as well as bioremediation applications.
We thank the anonymous reviewers for their insightful comments
and suggestions regarding the manuscript.
This work was supported by grant DACA72-00-C-0016 from the
U.S. Department of Defense to J.D.C. and L.A.A.
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FIG. 7. Slot blot hybridization of genomic DNAs from DPRB and
non-perchlorate-reducing close relatives of DPRB using the D. agitata
pcrA probe. A total of 250 ng of genomic DNA was loaded for each
strain. Row A (left to right): 1, D. agitata; 2, R. tenuis; 3, D. aromatica;
4, Dechloromonas sp. strain JJ. Row B: 1, D. anomolous strain WD; 2,
M. magnetotacticum; 3, Pseudomonas sp. strain PK; 4, P. stutzeri. Row
C: 1, D. chlorophilus strain NSS; 2, A. suillum; 3, Dechloromonas sp.
strain LT-1; 4, I. dechloratans. D. agitata, D. aromatica, D. anomalous,
A. suillum, and Dechloromonas sp. strain LT-1are capable of perchlor-
ate reduction; Pseudomonas sp. strain PK, D. chlorophilus strain NSS,
and I. dechloratans are capable of only chlorate reduction.
VOL. 187, 2005PERCHLORATE REDUCTASE GENES 5095
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