The K+ uptake regulator TrkA controls membrane potential, pH homeostasis and multidrug susceptibility in Mycobacterium smegmatis

Background: Rifampicin is an important first-line antibiotic for the treatment of mycobacterial infections. Although most rifampicin-resistant strains arise through mutations in the rpoB gene in bacteria, a proportion of such strains show no rpoB mutations. This suggests that alternative mechanisms are responsible for rifampicin resistance. Methods: We have constructed and analysed a library of 11000 Mycobacterium smegmatis insertion mutants to find other possible rifampicin-resistance determinants. Results: We found that disruption of trkA, a putative regulator of K+ uptake, leads to increased rifampicin resistance. Our data indicate that TrkA-mediated K+ uptake is essential for maintenance of the M. smegmatis growth rate, its pH homeostasis and membrane potential. In addition to increased rifampicin resistance, inactivation of trkA confers resistance to other hydrophobic agents, such as novobiocin, as well as increased susceptibility to isoniazid and positively charged aminoglycosides. Conclusions: Our results suggest that trkA is a general regulator of antibiotic susceptibility, and the changes in the multidrug susceptibility/resistance pattern detected in the trkA mutant are associated with membrane hyperpolarization. This study sheds light on the role of ion transport activity in intrinsic and acquired antibiotic resistance in mycobacteria.