The CopRS Two-Component System Is Responsible for Resistance to Copper in the Cyanobacterium Synechocystis sp. PCC 6803      

Abstract

Photosynthetic organisms need copper for cytochrome oxidase and for plastocyanin in the fundamental processes of respiration and photosynthesis. However, excess of free copper is detrimental inside the cells and therefore organisms have developed homeostatic mechanisms to tightly regulate its acquisition, sequestration, and efflux. Herein we show that the CopRS two-component system (also known as Hik31-Rre34) is essential for copper resistance in Synechocystis sp. PCC 6803. It regulates expression of a putative heavy-metal efflux-resistance nodulation and division type copper efflux system (encoded by copBAC) as well as its own expression (in the copMRS operon) in response to the presence of copper in the media. Mutants in this two-component system or the efflux system render cells more sensitive to the presence of copper in the media and accumulate more intracellular copper than the wild type. Furthermore, CopS periplasmic domain is able to bind copper, suggesting that CopS could be able to detect copper directly. Both operons (copMRS and copBAC) are also induced by the photosynthetic inhibitor 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone but this induction requires the presence of copper in the media. The reduced response of two mutant strains to copper, one lacking plastocyanin and a second one impaired in copper transport to the thylakoid, due to the absence of the PI-type ATPases PacS and CtaA, suggests that CopS can detect intracellular copper. In addition, a tagged version of CopS with a triple HA epitope localizes to both the plasma and the thylakoid membranes, suggesting that CopS could be involved in copper detection in both the periplasm and the thylakoid lumen.

Using Transcriptomics To Improve Butanol Tolerance of Synechocystis sp. Strain PCC 6803

“…The induction of expression of this operon was likely due to degradation of the electron carrier plastocyanin and subsequent release of bound copper. A similar upregulation was previously observed upon addition of DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p- benzoquinone), which blocks electron transfer to PC and oxidizes the PC pool (47).…”

An Intimate Link: Two-Component Signal Transduction Systems and Metal Transport Systems in Bacteria

“…PCC 6803, CopRS two-component system is known to be essential for copper resistance [42]. CopS was shown to have a high affinity to bind Cu in vitro , moreover its localization both in the plasma and thylakoid membrane suggested that CopS can possibly bind and respond to Cu both in the periplamic and thylakoid lumen in Synechocystis [42]. However, further studies are warranted to completely understand the mechanism and conditions involved in Cu binding to CopS under natural conditions.…”

Copper-responsive gene regulation in bacteria

“…The isolated periplasmic domain of the sensor kinase CopS binds Cu 2+ but not Zn 2+ , Ni 2+ or Co 2+ , suggesting that CopS specifically responds to copper (Giner-Lamia et al, 2012). Direct repeat sequences (TTTCAT-N 5 -TTTCAT) upstream of the copBAC and copMRS transcription start sites are thought to act as binding sites of the response regulator CopR.…”

“…The unicellular cyanobacterium Synechocystis 6803 synthesizes a plasmid-borne RND-type copper efflux system encoded by the copBAC operon to cope with excess copper (Giner-Lamia et al, 2012). Either of two genetically distinct two-component CopRS systems (encoded by the chromosomal copMRS and the episomal pcopMRS operons) is sufficient to induce copBAC expression.…”