Environmental Engineering Reference
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pathway is fully induced. Seto et al. (1996) have suggested that chlorinated
HOPDA or its metabolites inhibited growth of wild-type RHA1. We observed
that with biphenyl-grown inoculum there was no 4-CB growth, even though
formation of HOPDA was rapid and intense.
The PCB degradation range of the RHA1(pRHD34:: fcb ) was examined
in biphenyl-grown resting cell assays. We observed complete degradation
of 2-, 4-, and 2,4-CB after 24 h of incubation. Accumulation of equimolar
amounts of 2- and 2,4-CBA was observed; however, no 4-CBA was detected,
whereas the parent RHA1 accumulated stoichiometric quantities of 4-CBA
from 4-CB. This suggested activity of the enzymes encoded by the fcb operon
in the recombinant strain. Because the wild-type strain RHA1 could degrade
the major products from pattern M anaerobic dechlorination with a theoret-
ical recovery of 50% of para-chlorobenzoates (Maltseva et al., 1999), we tested
the activity of the recombinant strain with mix M. Similar degradation rates
for mixture M congeners by the wild-type RHA1 and its recombinant were
observed, with 60% of mix M PCBs degraded. However, whereas the parent
RHA1 accumulated 2-, 4-, and 2,4-CBAs, only trace concentrations of 4-CBA
were found in recombinant RHA1(pRHD34:: fcb ) (Figure 6.10). Notably,
HOPDA concentrations were 38% less for the recombinant strain, possibly
due to partial removal of the bottleneck presented by CBAs. Final concen-
trations of 2- and 2,4-CBA were similar for both wild-type and transformant
strain, with no utilization of these metabolites in either case (Rodrigues et
al., 2001).
Chlorobipheny1, uM
A
Mix M
150
Chlorobenzoate, uM
300
250
200
150
100
50
0 0
B
100
50
0
A
Mix M + RHA1 (+ fcb )
4
8
12
Time, h
16
20
24
150
2-CBA
4-CBA
2, 4-CBA
100
Degradation of Mix M by the
resting cells of Rhodococcus sp.
RHA1 (+ fcb ) (A) and accumulation
of a chlorobenzoates (B).
50
0
2-CB
4-CB
2-2
/2, 6-CB
2, 4-CB
2-4
-CB
2, 4-2
-CB
2, 4-4
-CB
Figure 6.10 Degradation of m ix M by RHA1( fcb ).
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