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Journal of Bacteriology, May 2000, p. 2687-2695, Vol. 182, No. 10
Institut für Mikrobiologie, Swiss
Federal Institute of Technology, ETH-Zentrum, CH-8092 Zürich,
Switzerland
Received 23 December 1999/Accepted 16 February 2000
The Escherichia coli tauABCD and ssuEADCB
gene clusters are required for the utilization of taurine and
alkanesulfonates as sulfur sources and are expressed only under
conditions of sulfate or cysteine starvation. tauD and
ssuD encode an
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Deletion Analysis of the Escherichia
coli Taurine and Alkanesulfonate Transport Systems
-ketoglutarate-dependent taurine
dioxygenase and a reduced flavin mononucleotide-dependent alkanesulfonate monooxygenase, respectively. These enzymes are responsible for the desulfonation of taurine and alkanesulfonates. The
amino acid sequences of SsuABC and TauABC exhibit similarity to those
of components of the ATP-binding cassette transporter superfamily,
suggesting that two uptake systems for alkanesulfonates are present in
E. coli. Chromosomally located in-frame deletions of the
tauABC and ssuABC genes were constructed in
E. coli strain EC1250, and the growth properties of the
mutants were studied to investigate the requirement for the TauABC and
SsuABC proteins for growth on alkanesulfonates as sulfur sources.
Complementation analysis of in-frame deletion mutants confirmed that
the growth phenotypes obtained were the result of the in-frame
deletions constructed. The range of substrates transported by these two uptake systems was largely reflected in the substrate specificities of
the TauD and SsuD desulfonation systems. However, certain known substrates of TauD were transported exclusively by the SsuABC system.
Mutants in which only formation of hybrid transporters was possible
were unable to grow with sulfonates, indicating that the individual
components of the two transport systems were not functionally
exchangeable. The TauABCD and SsuEADCB systems involved in
alkanesulfonate uptake and desulfonation thus are complementary to each
other at the levels of both transport and desulfonation.
*
Corresponding author. Mailing address: Institut
für Mikrobiologie, ETH-Zentrum, CH-8092 Zürich,
Switzerland. Phone: 41 1 632 33 24. Fax: 41 1 632 11 48. E-mail:
leisinger{at}micro.biol.ethz.ch.
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