Zn²⁺/Cd²⁺ EFFLUX PUMPS CONFER ROBUST RESISTANCE TO ORGANIC ACIDS

Organic acids are known to inhibit bacterial growth. They permeate into cells, undergo de-protonation, disrupt the proton motive force (∆pH) and membrane potential (∆ψ) and also directly inhibit metabolic pathways. Accordingly, organic acids are often used as food preservatives. However, there is a substantial commercial interest on identifying conditions or bacterial strains enabling more efficient bioreactor production of organic acids, as possible alternatives to common petrochemicals. Therefore, bacterial tolerance to organic acids is of substantial clinical and commercial interest.

P-type ATPases are a large and ubiquitous family of trans-membrane ATPases that utilize ATP hydrolysis to drive translocation of various molecules. The P_IB-ATPases subgroup are efflux pumps of transition metals such as Cu⁺, Ag⁺, Zn²⁺, Cd²⁺ or Pb²⁺. Cu⁺ and Zn²⁺ are essential co-factors to many cellular functions, yet in high intracellular concentrations they are highly toxic. P_IB-ATPases maintain a delicate balance between essential import and toxic overload of both essential and non-essential transition metals. Mutations in human P_IB-ATPases lead to severe pathologies. Furthermore, P_IB-ATPases are essential for virulence of microbial pathogens, and there is also evidence implicating them with cancer drug resistance.

Here we report that expression of Zn²⁺/Cd²⁺ P_IB-ATPases confers bacteria with robust resistance to organic acids. The data suggests that organic acids increase the influx of metals into bacterial cells, thus leading to increased metal sensitivity. P_IB-ATPases reduces the intracellular metal concentrations to tolerable levels.

These results provide a stepping-stone for a more efficient use of organic acids as antibacterial agents and for their cost-effective bioreactor production.