Metals in Cyanobacteria: Analysis of the Copper, Nickel, Cobalt and Arsenic Homeostasis Mechanisms

Abstract

Traces of metal are required for fundamental biochemical processes, such as photosynthesis and respiration. Cyanobacteria metal homeostasis acquires an important role because the photosynthetic machinery imposes a high demand for metals, making them a limiting factor for cyanobacteria, especially in the open oceans. On the other hand, in the last two centuries, the metal concentrations in marine environments and lake sediments have increased as a result of several industrial activities. In all cases, cells have to tightly regulate uptake to maintain their intracellular concentrations below toxic levels. Mechanisms to obtain metal under limiting conditions and to protect cells from an excess of metals are present in cyanobacteria. Understanding metal homeostasis in cyanobacteria and the proteins involved will help to evaluate the use of these microorganisms in metal bioremediation. Furthermore, it will also help to understand how metal availability impacts primary production in the oceans. In this review, we will focus on copper, nickel, cobalt and arsenic (a toxic metalloid) metabolism, which has been mainly analyzed in model cyanobacterium Synechocystis sp. PCC 6803.

The cobalt cycle in the Tropical Pacific Ocean

“…A second, connected strategy is simply to export toxic metals out of the cell by expressing periplasmic metal pumps (Badarau and Dennison, 2011;Huertas et al, 2014). Export systems for Cu, Zn, Ni, and Co have all been identified in cyanobacteria (Huertas et al, 2014). These mechanisms combine such that free metal concentrations in cyanobacteria (Synechocystis) are the reverse of the Irving Williams series: Cu'<<Ni'<Zn'<Co',Fe', and Mn' (Patterson et al, 2013b;).…”

“…Production of a cytosolic Cubinding protein by the cyanobacterium Synechocystis 6803, for instance, decreases Cu' availability and enables Mn proteins to be properly metallated (Tottey et al, 2008). A second, connected strategy is simply to export toxic metals out of the cell by expressing periplasmic metal pumps (Badarau and Dennison, 2011;Huertas et al, 2014). Export systems for Cu, Zn, Ni, and Co have all been identified in cyanobacteria (Huertas et al, 2014).…”

“…Prochlorococcus lacks homologous genes to most metal chaperones and export pumps that have been characterized in model cyanobacteria like Synechocystis (Table 1) (Huertas et al, 2014).…”

Upregulation of thiamine (vitamin B1) biosynthesis gene upon stress application inAnabaenasp. andNannochloropsis oculata

“…Oxidative stress due to the accumulation of metals will cause lipid peroxidation, nucleic acid damage and inhibition of essential metabolism (Huertas et al 2014). Copper and sodium hypochlorite have been used to generate oxidative stress.…”

“…Even though copper is an essential micronutrient to aquatic life, it can be toxic at concentration as low as 1 µgL -1 (Levy et al 2007). Formation of hydroxyl radicals through Haber-Weiss and Fenton reaction are triggered by redox active metal as copper can transform between two oxidative stages (Srivastava et al 2005;Huertas et al 2014). Sodium hypochlorite (NaOCl) is a form of a bleaching agent widely used in industry.…”