The Mechanism of Iron Homeostasis in the Unicellular Cyanobacterium Synechocystis sp. PCC 6803 and Its Relationship to Oxidative Stress    

Abstract

In this article, we demonstrate the connection between intracellular iron storage and oxidative stress response in cyanobacteria. Iron is essential for the survival of all organisms. However, the redox properties that make iron a valuable cofactor also lead to oxidative interactions, resulting in the formation of harmful radicals. Therefore, iron accumulation in cells should be tightly regulated, a process in which ferritin family proteins play an important role. Synechocystis sp. PCC 6803 contains two ferritintype storage complexes, bacterioferritin and MrgA. Previous studies demonstrated the role of bacterioferritin and MrgA in iron storage. In addition, MrgA was found to play a key role in oxidative stress response. Here, we examined the dual role of the ferritin family proteins using physiological and transcriptomic approaches. Microarray analysis of iron-limited wild-type and DmrgA cultures revealed a substantial up-regulation of oxidative stress-related genes in mutant cells. The PerR regulator was found to play an important role in that process. Furthermore, we were able to demonstrate the connection between internal iron quota, the presence of the two storage complexes, and the sensitivity to externally applied oxidative stress. These data suggest a pivotal role for the ferritin-type proteins of Synechocystis sp. PCC 6803 in coordinating iron homeostasis and in oxidative stress response. The combined action of the two complexes allows for the safe accumulation and release of iron from storage by minimizing damage resulting from interactions between reduced iron and the oxygen radicals that are produced in abundance by the photosynthetic apparatus.

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake

“…First, iron demand is much higher in photosynthetic cyanobacteria than in nonphotosynthetic bacteria because of its use in the photosynthetic electron transport chain. Indeed, estimates are that the cyanobacteria require 10-fold more iron than bacteria of similar cell size to maintain photosynthetic activity (Raven et al, 1999;Shcolnick et al, 2009). Without TonB-ExbBExbD-dependent active uptake pathway, cyanobacterial cells might rely on passive transport of iron through porins, which may provide insufficient iron for photosynthesis.…”

Long-Term Acclimation to Iron Limitation Reveals New Insights in Metabolism Regulation of Synechococcus sp. PCC7002

“…Acclimation to different Fe' concentrations is essential to directly investigate the physiological and transcriptomic responses resulting from Fe homeostasis (Mock and Hoch, 2005). Typically, transcriptomic studies, report short-term responses to Fe stress induced by starvation through omission of Fe in the culture medium (Nodop et al, 2008;Jiang et al, 2015) or addition of a strong Fe binding ligand such as desferrioxamine B (Shcolnick et al, 2009;Ludwig and Bryant, 2012). However, with exception of final phases of a phytoplankton bloom, abrupt increase in Fe limitation is not common in marine environment.…”

The iron content and ferritin contribution in fresh, dried, and toasted nori, Pyropia yezoensis

“…19,[38][39][40] On the other hand, ferritin contribution to iron storage in macroalgae or seaweeds is explored only recently, 24) although a ferritin gene is described as a stress-induced gene in a green seaweed Ulva sp. 41) Algae have developed sophisticated mechanisms for iron acquisition and storage, because onethird of the ocean is assumed to be deficient in iron due to its extremely low solubility in the oxidized state.…”