Dispensa M, Thomas CT, Kim MK, Perrotta JA, Gibson J, Harwood CS.
Anaerobic growth of Rhodopseudomonas palustris on 4-hydroxybenzoate is dependent
on AadR, a member of the cyclic AMP receptor protein family of transcriptional
J Bacteriol. 1992 Sep;174(18):5803-13.
The purple nonsulfur phototrophic bacterium Rhodopseudomonas palustris converts
structurally diverse aromatic carboxylic acids, including lignin monomers, to
benzoate and 4-hydroxybenzoate under anaerobic conditions. These compounds are
then further degraded via aromatic ring-fission pathways. A gene termed aadR, for
anaerobic aromatic degradation regulator, was identified by complementation of
mutants unable to grow anaerobically on 4-hydroxybenzoate. The deduced amino acid
sequence of the aadR product is similar to a family of transcriptional regulators
which includes Escherichia coli Fnr and Crp, Pseudomonas aeruginosa Anr, and
rhizobial FixK and FixK-like proteins. A mutant with a deletion in aadR failed to
grow on 4-hydroxybenzoate under anaerobic conditions and grew very slowly on
benzoate. It also did not express aromatic acid-coenzyme A ligase II, an enzyme
that catalyzes the first step of 4-hydroxybenzoate degradation, and it was
defective in 4-hydroxybenzoate-induced expression of benzoate-coenzyme A ligase.
The aadR deletion mutant was unaffected in other aspects of anaerobic growth. It
grew normally on nonaromatic carbon sources and also under nitrogen-fixing
conditions. In addition, aerobic growth on 4-hydroxybenzoate was
indistinguishable from that of the wild type. These results indicate that AadR
functions as a transcriptional activator of anaerobic aromatic acid degradation.
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