Redundant genes encoding potassium transporter systems guarantee the survival of enterococcus faecalis in low potassium medium under stress conditions

ACCIARRI, G; ESPARIZ, M; BLANCATO, VICTOR; MAGNI, C

Congreso; LVII Reunión Anual de SAIB; 2021

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

A natural commensal member of the human gut flora that belongs to the group of lactic acid bacteria, Enterococcus faecalis is also a clinically important opportunistic pathogen. Despite its controversial profile, E. faecalis is part of food products, either due to contamination or as part of starter, adjunct or non-starter cultures. A distinct trait in the physiology of these bacteria is the ability to persist and thrive in harsh environments, that include heat, acid, oxidative and hyperosmotic stress. This tolerance to stress conditions involves the rapid movement of three critical ions: proton (H+), sodium (Na+), and potassium (K+). In E. faecalis the activity of the proton F0F1ATPase and the sodium Na V-type ATPase under acidic or alkaline conditions, respectively are well established. However, little is known about the K+ metabolism. In this study, an initial survey was done on K+ uptake in E. faecalis. The mining of E. faecalis genome revealed the presence of the putative K+ transporters Kup, KimA, Ktr, and Kdp. Distribution of these transporters was not conserved among different strains of this species. In addition, evidence shows that the reduction of K+ in the culture medium reduces the growth of E. faecalis JH2-2 as well as its resistance to acidic and osmotic stresses. To further examine the role of E. faecalis Kup, KimA, and KtrA proteins in K+ transport, the growth of different K+ transporter mutants in E. faecalis JH2-2 was tested in a low K+ medium at acidic, neutral, and alkaline starting pH.Whereas deletion of either kup or kimA alone and deletion of both genes had no impact on growth either under neutral or alkaline conditions, the ΔktrA mutant showed a defect on growth at pH 9. The Δkup ΔktrA mutant exhibited a defect in growth in neutral and alkaline starting pH, which was more marked at pH9. Hence, both E. faecalis Ktr and Kup systems were shown to be important for low-K+ growth under alkaline conditions. In all cases, the addition of KCl to the low K + medium improved the growth of the defective strains. Finally, the fact that the Δkup ΔkimA ΔktrA mutant strain could not be obtained so far suggests that at least one of the K+ uptake system studied must be active in E. faecalis JH2-2. Taken together, these results underline the importance of K+ uptake in maintaining essential components, such as pH homeostasis, osmoregulation, membrane potential, or protein synthesis, of E. faecalis to resist, persist and growth in extreme stress environments.