Biomedical Engineering Reference
In-Depth Information
Inoculation
Mixing for
base addition
Acetate = 100 mg/L
50 mg/L
Day 25
102
116
122-125
167
314
641
12.0
24.0
1
5
NO 3 [ppm]
Distance from
delivery wells (m)
0 0 0 0 0 0
Figure 9.17. Krieged images showing changes over time in nitrate concentrations in the monitor-
ing wells downgradient from the delivery well gallery. Results are shown for Transect A in
Figure 9.13 . CF was detected during a period of sulfate-reduction. Prevention of CF formation by
decreasing acetate addition, led to an increase in nitrate levels, as illustrated for day 641.
Reprinted with permission from Dybas et al., 2002 . Copyright 2002, American Chemical Society.
9.9 FUTURE USE OF PSEUDOMONAS STUTZERI
KC AND PDTC
A potential exists for genetic engineering of P. stutzeri KC, with introduction of genes
encoding PDTC synthesis into other organisms. Gene 'cassettes' are now available that can be
used to transfer PDTC synthesis capability using a variety of vectors, with potential for
increased expression and broad host range compatibility. The ability to produce PDTC may
confer competitive advantages for such genetically-engineered strains. Physiological data
indicate that any organism that can produce PDTC must have the components needed to
make use of it. Without those components, the organisms would likely be subject to PDTC-
imposed growth inhibition (Leach and Lewis, 2006 ; Sebat et al., 2001 ). However, the minimal
set of genes required for PDTC production are not yet known, and the biosynthetic pathway
and central metabolic pathways that supply starting materials for PDTC production are not yet
fully elucidated.
Initial observations with recombinant E. coli (another gamma proteobacterium) or Sinor-
hizobium meliloti (an alpha proteobacterium) containing plasmid-borne pdt gene clusters have
not shown PDTC production (Lewis et al., 2000 ). The reasons for this apparently
phylogenetically-restricted capability to support PDTC production are not known. It is possible
that components resulting from Pseudomonas -specific gene expression are necessary, or that
metabolites unique to pseudomonads are used as feedstock for PDTC biosynthesis. Data of
Sepulveda-Torres et al. ( 2002 ) support the second possibility in that they showed at least modest
transcription from the pdt F KC promoter by E. coli .
Though strategies that may lead to increased transcription of pdt genes could be engi-
neered, for example by removing fur -binding sites or replacing pdt promoters with more active
alternative promoters, it is not known whether this would truly affect greater PDTC production
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