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Journal of Bacteriology, February 1999, p. 791-798, Vol. 181, No. 3
Department of Biology and Biochemistry,
University of Houston, Houston, Texas 77204-5513
Received 25 August 1998/Accepted 19 November 1998
The permeability of the outer membrane of Escherichia
coli to hydrophilic compounds is controlled by porin channels.
Electrophysiological experiments showed that polyamines inhibit ionic
flux through cationic porins when applied to either side of the
membrane. Externally added polyamines, such as cadaverine, decrease
porin-mediated fluxes of
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Excretion of Endogenous Cadaverine Leads to a
Decrease in Porin-Mediated Outer Membrane Permeability
-lactam antibiotics in live cells. Here we
tested the effects of endogenously expressed cadaverine on the rate of
permeation of cephaloridine through porins, by manipulating in a
pH-independent way the expression of the cadBA operon,
which encodes proteins involved in the decarboxylation of lysine to
cadaverine and in cadaverine excretion. We report that increased levels
of excreted cadaverine correlate with a decreased outer membrane
permeability to cephaloridine, without any change in porin expression.
Cadaverine appears to promote a sustained inhibition of porins, since
the effect remains even after removal of the exogenously added or excreted polyamine. The cadaverine-induced inhibition is sufficient to
provide cells with some resistance to ampicillin but not to hydrophobic
antibiotics. Finally, the mere expression of cadC, in the
absence of cadaverine production, leads to a reduction in the amounts
of OmpF and OmpC proteins, which suggests a novel mechanism for the
environmental control of porin expression. The results presented here
support the notion that polyamines can act as endogenous modulators of
outer membrane permeability, possibly as part of an adaptive response
to acidic conditions.
*
Corresponding author. Mailing address: Department of
Biology and Biochemistry, University of Houston, Houston, TX
77204-5513. Phone: (713) 743-2684. Fax: (713) 743-2636. E-mail:
adelcour{at}uh.edu.
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