Global Transcriptional Profiles of the Copper Responses in the Cyanobacterium <i>Synechocystis</i> sp. PCC 6803

Abstract

<div><p>Copper is an essential element involved in fundamental processes like respiration and photosynthesis. However, it becomes toxic at high concentration, which has forced organisms to control its cellular concentration. We have recently described a copper resistance system in the cyanobacterium <i>Synechocystis</i> sp. PCC 6803, which is mediated by the two-component system, CopRS, a RND metal transport system, CopBAC and a protein of unknown function, CopM. Here, we report the transcriptional responses to copper additions at non-toxic (0.3 µM) and toxic concentrations (3 µM) in the wild type and in the copper sensitive <i>copR</i> mutant strain. While 0.3 µM copper slightly stimulated metabolism and promoted the exchange between cytochrome c₆ and plastocyanin as soluble electron carriers, the addition of 3 µM copper catalyzed the formation of ROS, led to a general stress response and induced expression of Fe-S cluster biogenesis genes. According to this, a double mutant strain <i>copRsufR</i>, which expresses constitutively the <i>sufBCDS</i> operon, tolerated higher copper concentration than the <i>copR</i> mutant strain, suggesting that Fe-S clusters are direct targets of copper toxicity in <i>Synechocystis</i>. In addition we have also demonstrated that InrS, a nickel binding transcriptional repressor that belong to the CsoR family of transcriptional factor, was involved in heavy metal homeostasis, including copper, in <i>Synechocystis</i>. Finally, global gene expression analysis of the <i>copR</i> mutant strain suggested that CopRS only controls the expression of <i>copMRS</i> and <i>copBAC</i> operons in response to copper.</p></div