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Dibutyl phthalate (DBP) is one of the most abundant toxic phthalate ester contaminants in the environment. Two esterase genes, estB and estG, were cloned from Sphingobium sp. SM42, which could utilize an endocrine disrupting dibutyl phthalate as a sole carbon source. EstG, which shares sequence identity with very few proteins, showed a greater capacity to breakdown DBP, both in vitro and in vivo, compared to EstB. estG and estBG insertional inactivation mutants could not degrade DBP mainly due to the absence of the efficient DBP-transforming enzyme, EstG. Interestingly, the estB mutant degraded DBP better than the parent strain. The result of RT-PCR experiments confirm that estB mutants compensate for the loss of EstB by an increase in the expression of estG and this process enables Sphingobium to degrade more DBP. A gene designated estR, encoding a MarR family protein, was found upstream of estB. An estR-overexpressing strain showed an increased level of estB mRNA relative to wild-type. EstR is thus a positive transcriptional regulator that mediates the induction of estB esterase expression but it is not involved in the observed compensatory increase in expression of estG in the estB mutant. |
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