DEHALOCOCCOIDES AND REDUCTIVE DECHLORINATION OF CHLORINATED SOLVENTS - Bioaugmentation for Groundwater Remediation - page 64

Table 2.6. Dhc RDase Genes with Assigned Function

Molecular Mass b
[kDa]

Reaction
Catalyzed Gene Dhc RDase Reference

pceA PceA PCE ! TCE 50,800 Magnuson et al.,

2000

tceA TceA TCE ! VC 57,700 Magnuson et al.,

2000

vcrA VcrA DCEs,

VC ! ethene

53,100 M¨ ller et al., 2004

BvcA a VC ! ethene a bvcA 52,800 Krajmalnik-Brown

et al., 2004

cbrA CbrA 1,2,3,4-

TeCB ! 1,2,
4-TCB

49,700 Adrian et al., 2007b

a The function of BvcA has not been biochemically verified and the information shown was drawn from transcriptional
data
b Molecular masses without the Tat leader peptide deduced from the rdhA sequence

involved in electron transfer. Dhc RDase B proteins are 76-100 amino acids long with 2-3
predicted transmembrane spanning regions suggesting they are integral membrane proteins
(Maillard et al., 2003 ; Villemur et al., 2002 ). Dhc RDases are associated with the membrane
fraction, and the current models suggest that the RdhB proteins anchor the RdhA enzymes to
the outside of the cytoplasmic membrane (M¨ller et al., 2004 ).

2.9 BIOCHEMISTRY OF REDUCTIVE DECHLORINATION
BY DEHALOCOCCOIDES
Although the details of electron transport in Dhc are not well explored, it is likely that one
or more of the five hydrogenase complexes encoded on the Dhc genomes is responsible for the
initial uptake of electrons from hydrogen. The mechanisms and components involved in
electron transfer from the hydrogenase complex(es) to the terminal reductase (i.e., the specific
RDase) are unclear and direct electron transfer from the hydrogenase to the RDase (i.e.,
without intermediate electron carriers) is being discussed.
The reasons why Dhc possess five gene clusters encoding potential hydrogenase enzyme
complexes to do the simple reaction of removing electrons from protons in hydrogen (i.e.,
hydrogen oxidation: H 2 2H + +2e ) are unclear, but suggest that Dhc have a fine-tuned

response to fluctuating environmental hydrogen concentrations. Using proteomic techniques,
peptides (i.e., short amino acid chains) from three of these predicted hydrogenases (Figure 2.6 )
were detected in strain 195 membrane fractions derived from biomass grown in medium
amended with PCE and hydrogen (Morris et al., 2006 ). The highest peptide coverage, which is
a semi-quantitative measure of protein abundance, was obtained for the Hup hydrogenase,
predicted to have its catalytic subunit on the outside the cell membrane. Detected in lower
abundance were peptides of the Vhu and Hym hydrogenases. Thus, these three hydrogenases are
candidates for being quantitatively relevant hydrogenases during growth of strain 195 with PCE.
Quinones are well known hydrophobic and membrane-associated organic molecules
that participate in electron transport, and high amounts of ubiquinone and lower amounts of

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