Multidrug resistance protein MdtM adds to the repertoire of antiporters involved in alkaline pH homeostasis in Escherichia coli

BMC Microbiology

Research Article

Scarlett R Holdsworth¹  Christopher J Law¹ 

[1] Institute for Global Food Security, School of Biological Sciences, Medical Biology Centre, Queen’s University Belfast, 97 Lisburn Road, BT9 7BL, Belfast, UK;

关键词: Major Facilitator Superfamily;    Multicopy Plasmid;    Alkaline Stress;    Monovalent Metal;    Acridine Orange Fluorescence;   

DOI  :  10.1186/1471-2180-13-113

 received in 2013-03-06, accepted in 2013-05-20,  发布年份 2013

来源: Springer

【 摘 要 】

BackgroundIn neutralophilic bacteria, monovalent metal cation/H+ antiporters play a key role in pH homeostasis. In Escherichia coli, only four antiporters (NhaA, NhaB, MdfA and ChaA) are identified to function in maintenance of a stable cytoplasmic pH under conditions of alkaline stress. We hypothesised that the multidrug resistance protein MdtM, a recently characterised homologue of MdfA and a member of the major facilitator superfamily, also functions in alkaline pH homeostasis.ResultsAssays that compared the growth of an E. coli ΔmdtM deletion mutant transformed with a plasmid encoding wild-type MdtM or the dysfunctional MdtM D22A mutant at different external alkaline pH values (ranging from pH 8.5 to 10) revealed a potential contribution by MdtM to alkaline pH tolerance, but only when millimolar concentrations of sodium or potassium was present in the growth medium. Fluorescence-based activity assays using inverted vesicles generated from transformants of antiporter-deficient (ΔnhaA, ΔnhaB, ΔchaA) E. coli TO114 cells defined MdtM as a low-affinity antiporter that catalysed electrogenic exchange of Na+, K+, Rb+ or Li+ for H+. The K+/H+ antiport reaction had a pH optimum at 9.0, whereas the Na+/H+ exchange activity was optimum at pH 9.25. Measurement of internal cellular pH confirmed MdtM as contributing to maintenance of a stable cytoplasmic pH, acid relative to the external pH, under conditions of alkaline stress.ConclusionsTaken together, the results support a role for MdtM in alkaline pH tolerance. MdtM can therefore be added to the currently limited list of antiporters known to function in pH homeostasis in the model organism E. coli.

【 授权许可】

CC BY   
© Holdsworth and Law; licensee BioMed Central Ltd. 2013