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Journal of Bacteriology, April 2000, p. 2088-2095, Vol. 182, No. 8
Department of Biochemistry and Molecular
Biology, Mount Sinai School of Medicine, New York, New York
10029,1 and Department of Life Science,
Toyo University, Oura-gun, Gunma 374-0193, Japan2
Received 3 December 1999/Accepted 20 January 2000
The chromosomally encoded TetA(L) protein of Bacillus
subtilis is a multifunctional tetracycline-metal/H+
antiporter that also exhibits monovalent cation/H+ antiport
activity and a net K+ uptake mode. In this study, B. subtilis mutant strains JC112 and JC112C were found to be
representative of two phenotypic types of tetA(L) deletion
strains that are generated in the same selection. Both strains
exhibited increased sensitivity to low tetracycline concentrations as
expected. The mutants also had significantly reduced ability to grow in
media containing low concentrations of K+, indicating that
the net K+ uptake mode is of physiological consequence; the
deficit in JC112 was greater than in JC112C. JC112 also exhibited (i)
greater impairment of Na+- or K+-dependent
growth at pH 8.3 than JC112C and (ii) a greater degree of
Co+2 as well as Na+ sensitivity. Studies were
initiated to explore the possibility of two different patterns of
compensatory changes in other ion-translocating transporters in these
mutants. Increased expression of two loci has thus far been shown.
Increased expression of czcD-trkA, a locus with a proposed
involvement in K+ uptake, occurred in both mutants. The
increase was highest in the presence of Co2+ and was higher
in JC112 than in JC112C. Deletion of czcD-trkA resulted in
diminished growth of the wild-type and both mutant strains at low
[K+], supporting a significant role for this locus in
K+ uptake. Expression of yheL, which is a
homologue of the Na+/H+ antiporter-encoding
nhaC gene from Bacillus firmus OF4, was also increased in both tetA(L) deletion strains, again with
higher up-regulation in JC112. The phenotypes resulting from deletion of yheL were consistent with a modest role for YheL in
Na+-dependent pH homeostasis in the wild type. No major
role for YheL was indicated in the mutants in spite of the
overexpression. The studies underscore the multiple physiological
functions of TetA(L), including tetracycline, Na+, and
alkali resistance and K+ acquisition. The studies also
reveal and begin to detail the complexity of the response to mutational
loss of these functions.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Two Types of Bacillus subtilis tetA(L) Deletion
Strains Reveal the Physiological Importance of TetA(L) in
K+ Acquisition as well as in Na+, Alkali,
and Tetracycline Resistance
*
Corresponding author. Mailing address: Box 1020, Department of Biochemistry and Molecular Biology, Mount Sinai School of
Medicine, 1 Gustave L. Levy Place, New York, NY 10029. Phone: (212)
241-7280. Fax: (212) 996-7214. E-mail:
terry.krulwich{at}mssm.edu.
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