Biomedical Engineering Reference
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methanogens, may facilitate exchange of growth factors and/or nutrients including hydrogen
(Heimann et al.,
2006
; Schink,
1997
).
Obviously, understanding such microbe-microbe interactions is relevant for managing and
predicting dechlorination performance at bioremediation sites. The PCE-to-ethene-dechlorinat-
ing bioaugmentation consortium Bio-Dechlor INOCULUM (BDI) harbors multiple
Dhc
strains
and rapidly dechlorinates PCE to ethene in the absence of methanogens, indicating that
methanogenic archaea are not required for robust dechlorination activity, and other bacteria
(not Archaea) fulfill the nutritional requirements of
Dhc
(Amos et al.,
2008b
; Amos et al.,
2009
). As mentioned in Section
2.3.3
, strain FL2 was isolated from a robustly dechlorinating,
defined co-culture that included two unusual spirochete populations (FLiPS) that provide an as-
yet unknown benefit to
Dhc
(Ritalahti and L¨ffler,
2004a
,
b
,
2005
; Ritalahti,
2012
). Similarly,
strain DF-1, a PCB-dechlorinating
Dhc
relative obtained from Charleston Harbor sediment,
requires the presence of a
Desulfovibrio
sp. (or the addition of
Desulfovibrio
sp. cell extract)
for PCB dechlorination (May et al.,
2008
; Wu et al.,
2002
).
Dhc
strain 195 also benefits from the
presence of
Desulfovibrio desulfuricans
or
Acetobacterium woodii
(He et al.,
2007
). The
availability of pure cultures of
Dhc
and
Dhc
relatives along with isolates that apparently
provide growth factors and/or other services to the dechlorinators provide opportunities for
studying the interspecies interactions and
Dhc
ecology in more detail.
Another interesting observation that warrants further exploration is the occurrence of
multiple
Dhc
strains in the same environmental sample or enrichment. For example, micro-
cosms established with the same river sediment that yielded the TCE-dechlorinating
Dhc
isolate
strain FL2 also harbored
Dhc
strain RC1, which cannot dechlorinate chlorinated ethenes but
uses 1,2-dichoropropane as an electron acceptor (L¨ffler et al.,
1997a
; Ritalahti and L¨ffler,
2004a
). The PCE-to-ethene-dechlorinating consortia BDI, KB-1, ANAS and SDC-9 each contain
at least two
Dhc
strains with distinct dechlorination activities (Amos et al.,
2008a
,
2009
;
Duhamel et al.,
2004
; Holmes et al.,
2006
; Richardson et al.,
2002
; Vainberg et al.,
2009
).
During efforts aimed at isolating
Dhc
strain GT, a culture that contained only
Dhc
(and no
other microorganisms) was obtained initially. However, this early culture contained multiple
Dhc
strains, each with different RDase gene complements (Sung et al.,
2006b
). These findings
suggest that multiple
Dhc
strains with distinct dechlorination activities commonly coexist in the
same habitat and enrichment cultures. The consequences with respect to
Dhc
ecology and
bioremediation of an extensive RDase gene pool, contributed to by more than a single
Dhc
strain, remain to be explored.
2.14 OUTLOOK
The availability of pure cultures of
Dhc
and related bacteria, along with an increasing pool
of students trained to grow and maintain
Dhc
cultures, will provide new information regarding
the phylogenetic and functional diversity of these unique dechlorinating bacteria. Detailed
studies with community members that provide essential services to
Dhc
will unravel interspe-
cies interactions and generate new insights into
Dhc
nutritional requirements and ecology. The
outcomes will include improved culturability and allow a broader research community to study
these interesting organisms and facilitate the production of bioaugmentation consortia.
The expanding information gained from genome sequences will continue to reveal insight
into
Dhc
adaptation and evolution, as well as elucidate mechanisms and frequencies of RDase
gene mobilization and dissemination. Knowledge of reaction stoichiometries and reaction
kinetics will enable metabolomic flux modeling and generate more detailed understanding of
how
Dhc
respond to bioremediation treatment (e.g., electron donor addition) (Ahsanul Islam
et al.,
2010
). Combined with a comprehensive suite of molecular biological tools for monitoring
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