Engineering bacterial
strains through the chromosomal insertion of the Roberto Bobadilla* Cristián
Varela# Ricardo Céspedes§ Bernardo González * Corresponding author Financial support:
This work was supported by grants 1960262 and 8990004 from FONDECYT-Chile.
Chloroaromatic pollutants
from bleached Kraft pulp mill effluents (BKME) are difficult to degrade,
because bacterial strains present in BKME aerobic treatments, only
partially degrade these compounds, accumulating the corresponding
chlorocatechol intermediates. To improve the catabolic performance
of chlorocatechol-accumulating strains, we introduced, by chromosomal
insertion, the tfdICDEF gene cluster from Ralstonia
eutropha JMP134 (pJP4). This gene cluster allows dechlorination
and channelling of chlorocatechols into the intermediate metabolism.
Two bacterial strains, R. eutropha JMP222 and Pseudomonas
putida KT2442, able to produce chlorocatechols from 3-chlorobenzoate
(3-CB) were used. Acinetobacter lwoffii RB2 isolated from BKME
by its ability to grow on guaiacol as sole carbon source and shown
to be able to produce the corresponding chlorocatechols from the BKME
pollutants 4-, and 5-chloroguaiacol, was also used. The tfdICDEF
gene cluster was inserted in the chromosome of these strains using
miniTn5-derived vectors that allow expression of the Tfd enzymes
driven by the lacIq/Ptrc or tfdR/Ptfd-I
regulatory systems, and therefore, responding to the inducers isopropyl-ß-D-thiogalactopyranoside
(IPTG) or 3-CB, respectively. Crude extracts of cells from strains
JMP222, KT2442 or RB2 engineered with the tfd genes, grown
on benzoate and induced with IPTG or 3-CB showed Tfd specific activities
of about 15% - 80% of that of the strain JMP134. Dechlorination rates
for 3-CB or chloroguaiacols correlated with levels of Tfd enzymes.
However, none of the strains containing the chromosomal copy of the
tfdICDEF cluster grew on monochloroaromatics as
sole carbon source. Experiments with BKME aerobic treatment microcosms
showed that the catabolic performance of the engineered bacteria was
also lower than the wild-type R. eutropha strain JMP134. |
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