Affiliation:
1. Department of Microbiology, University of Iowa, Iowa City, Iowa 52242
Abstract
ABSTRACT
A cluster of genes for the anaerobic degradation of benzoate has been described for the phototrophic bacterium
Rhodopseudomonas palustris
. Here we provide an initial analysis of the regulation of anaerobic benzoate degradation by examining the contributions of two regulators: a new regulator, BadR, encoded by the benzoate degradation gene cluster, and a previously described regulator, AadR, whose gene lies outside the cluster. Strains with single mutations in either
badR
or
aadR
grew slowly on benzoate but were relatively unimpaired in growth on succinate and several intermediates of benzoate degradation. A
badR aadR
double mutant was completely defective in anaerobic growth on benzoate. Effects of the regulators on transcriptional activation were monitored with an
R. palustris
strain carrying a chromosomal fusion of ′
lacZ
to the
badE
gene of the
badDEFG
operon. This operon encodes benzoyl-coenzyme A (benzoyl-CoA) reductase, an unusual oxygen-sensitive enzyme that catalyzes the benzene ring reduction reaction that is the rate-limiting step in anaerobic benzoate degradation. Expression of
badE
::′
lacZ
was induced 100-fold when cells grown aerobically on succinate were shifted to anaerobic growth on succinate plus benzoate. The
aadR
gene was required for a 20-fold increase in expression that occurred in response to anaerobiosis, and
badR
was responsible for a further 5-fold increase in expression that occurred in response to benzoate. Further studies with the
badE
::′
lacZ
fusion strain grown with various kinds of aromatic acids indicated that BadR probably responds to benzoyl-CoA acting as an effector molecule. Sequence information indicates that BadR is a member of the MarR family of transcriptional regulators. These studies expand the range of functions regulated by MarR family members to include anaerobic aromatic acid degradation and provide an example of a MarR-type protein that acts as a positive regulator rather than as a negative regulator, as do most MarR family members. AadR resembles the
Escherichia coli
Fnr regulator in sequence and contains cysteine residues that are spaced appropriately to serve in the capacity of a redox-sensing protein.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
86 articles.
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