Selective metal ion homeostasis in cyanobacteria

© Springer Nature Singapore Pte Ltd. 2017. All rights reserved. Metal homeostasis systems are responsible for the uptake and efflux of both essential and non-essential metals. The capacity of these systems to acquire a particular metal, whilst excluding another is essential for the survival of not just cyanobacteria, but all organisms. The initial step in the acquisition of metal ions from the environment is the physiological binding, or adsorption, of metals to cells. The second step, often energy expensive, is the internalisation of metals, which is facilitated by uptake systems. Metal release from cells requires an efflux system. Both uptake and efflux systems may be controlled by their own regulatory elements. The effectiveness of these transport systems is dependent upon their ability to discriminate effectively between metals. This discrimination is achieved largely by the proteins involved comprising of different metal coordinating ligands strategically positioned in the tertiary structures. For cyanobacteria, arguably the most adept organisms at survival on earth, the information on metal coordination and binding is still limited. However, studies identifying and providing functional characterisation of metal transporters and metalloproteins in cyanobacteria are contributing new insights into metal homeostasis across all living organisms.