RESEARCH NEEDS FOR BIOAUGMENTATION - Bioaugmentation for Groundwater Remediation - page 342

Table 12.2. Combined Cultures have Broader Substrate Range and Alleviate Inhibition

Culture and Electron Acceptor

Dhb-TCA
1,1,1-TCA

KB-1 #
TCE

Dhb + KB-1 #
1,1,1-TCA and TCE Substrate

1,1,1-TCA + +

1,1-DCA + +

TCE + +

cis-DCE + +

VC + +

Organisms Multiple Dhb strains Multiple Dhc strains Dhb and Dhc

utilization of a wider variety of electron donors. This redundancy increases the flexibility of the
consortia and can lower the effective cost of a bioremediation effort.
Even though researchers understand the value of diversity and redundancy in the field, they
are often trapped by the enrichment paradox - in order for an enrichment consortium to be
understood and fully characterized, it needs to be simplified. Classic microbiological techni-
ques involve enrichment and isolation of target organisms, which is the easiest way to generate
a defined culture, which is then easier to describe for environmental certification processes
(e.g., by U.S. Environmental Protection Agency (USEPA) or Environment Canada). The simpler
the system becomes through an enrichment process, the stronger the questions that can be
asked using it, and the clearer the answers from those experiments. For research purposes,
especially for determining processes taking place, identifying enzymes integral to those
processes, and determining organismal roles, having a clean and simplified system is crucial.
However, the enrichment required for characterization of cultures generally also results in
lowered functional redundancy, slower growth and lowered degradative capacity, none of
which are ideal for use of the culture in an industrial setting or in research-based experiments.
For example, the bioaugmentation culture KB-1 # is typically maintained on TCE, with metha-
nol and ethanol as electron donors. It is a stable and robust culture containing multiple
dechlorinators (at least two Dehalococcoides and a Geobacter ) as well as many functionally
redundant supporting acetogens and methanogens. In an enrichment study, KB-1 # was main-
tained on VC alone, with hydrogen as an electron donor. After several transfers, the KB-1 #
culture had been enriched to essentially a co-culture of one Dehalococcoides strain and an
acetogen of the genus Sporomusa . While this system presented an excellent system for
examining dechlorination and was easily defined in terms of organismal diversity, the co-
culture had lost the ability to degrade PCE, and the rate of dechlorination had significantly
slowed. Together with the example from the WL enrichment process (Table 12.1 ), it is clear that
enrichment often leads to a decrease in degradative capability within the cultures, even though
it generates a simplified microbial system that is preferable for characterization and research.
In a deliberate attempt to maintain multiple species in an enrichment culture, the
WBC-2 culture (Jones et al., 2006 ) is maintained on multiple chlorinated substrates, including
1,1,2,2-tetrachloroethane, c is -1,2-dichloroethene ( cis- DCE) and 1,1,2-TCA, and two generic
electron donors, lactate and ethanol. This strategy does seem to hold advantages for maintain-
ing functional diversity and redundancy, yet makes dechlorination activity and microbial
population dynamics difficult to predict, particularly when any stress occurs. Indeed, the
WBC-2 culture is not very robust when diluted more than 10-fold, presumably as a result of