טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentZhitnitsky Daniel
SubjectUptake and Efflux of Transition Metals by Bacteria
DepartmentDepartment of Medicine
Supervisor Professor Oded Lewinson
Full Thesis textFull thesis text - English Version


Abstract

Transition metals play an indispensable role in all living cells. It is estimated that about half of all known enzymes require transition metals to function. Two of the most abundant transition metals used by the cell are copper and zinc. Despite their central roles, both copper and zinc are needed at low intracellular concentrations. At high intracellular concentrations all transition metals, even essential ones, are highly toxic. Thus, the homeostasis of transition metals must be strictly controlled, mainly by regulating influx and efflux metal transport proteins. While the bacterial uptake pathway for zinc is well characterized, much about copper’s biologic utilization remains unknown.

We identified and characterized an operon in E. coli, with previously unknown function. This operon is homologous to copper homeostasis systems in both Gram positive and Gram negative bacteria. We solved the 3-D structure of a periplasmic protein, encoded in this operon, which binds Cu2 with very high affinity, but does not bind Cu1. Furthermore, our data suggests this operon is essential for delivery of copper to copper-utilizing components of the bacterial electron transfer chain, for their proper expression and function.

            Due to their toxicity, transition metals have been exploited for millennia to inhibit bacterial growth. We report, the potentiation of the anti-bacterial activity of transition metals by organic acids (common food preservatives). We observed a strong synergy between low, non-toxic concentrations of transition metals and organic acids, with up to ~4000-fold higher inhibitory effect on bacterial growth when compared to their individual effects. We show that organic acids shuttle transition metals through the permeability barrier of the bacterial membrane, leading to increased influx of transition metals into bacterial cells. We further demonstrate that this synergy can be effectively used to inhibit the growth of a broad range of plant and human bacterial pathogens, suggesting a revision of food preservation and crop protection strategies.