Date of Award

5-16-2013

Document Type

Thesis

Degree Name

Bachelor of Arts

First Advisor

Slonczewski, Joan

Abstract

In Escherichia coli, TolC functions as the outer membrane channel to several multidrug resistance (MDR) pumps that utilize H+ influx to power substrate efflux. While evidence suggests that TolC may contribute to acid adaptation, the role of TolC in growth and survival at low pH remains unknown. Here, we describe the requirement of TolC and MDR efflux pump components EmrB and MdtB in acid adaptation. Both acid-adapted and non-adapted tolC mutants exhibited a decrease in extreme acid survival (acid resistance at pH 2). tolC mutants successfully resisted extreme acid when complemented by wild-type tolC, gadBC, and gadE genes. TolC was also required for optimal growth in moderate acid (pH 4.5 to 6.5) but not in neutral or basic pH conditions (pH 6.5 to 9.0). Both survival and growth at low pH were dependent on a functional, open TolC aperture. tolC defective strains complemented with either a closed TolC channel or non-functional TolC channel exhibited growth and survival comparable to the tolC mutant. TolC-dependent MDR efflux pump components EmrB and MdtB were also required for acid resistance but not moderate acid growth. A MDR efflux pump mutant lacking AcrB, AcrD, EmrB, EmrY, MdtC, MdtF, and AcrEF exhibited a modest decrease in acid resistance and no defect in moderate acid growth. Our findings suggest a novel physiological role for MDR efflux pump components in acid adaptation. TolC and the inner membrane pumps EmrB and MdtB helped E. coli survive extreme acid. TolC-mediated extreme acid survival involved the Gad acid resistance system and both survival and moderate acid growth required a functional TolC aperture capable of efflux. For enteric bacteria passing through the mammalian digestive tract, MDR efflux pumps may also confer heightened resistance to stomach acid.

Comments

Includes bibliographical references (p. 43-48)

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