A Gene Cluster Involved in Metal Homeostasis in the Cyanobacterium Synechocystis sp. Strain PCC 6803

Abstract

A gene cluster composed of nine open reading frames (ORFs) involved in Ni ²⁺ , Co ²⁺ , and Zn ²⁺ sensing and tolerance in the cyanobacterium Synechocystis sp. strain PCC 6803 has been identified. The cluster includes an Ni ²⁺ response operon and a Co ²⁺ response system, as well as a Zn ²⁺ response system previously described. Expression of the Ni ²⁺ response operon ( nrs ) was induced in the presence of Ni ²⁺ and Co ²⁺ . Reduced Ni ²⁺ tolerance was observed following disruption of two ORFs of the operon ( nrsA and nrsD ). We also show that the nrsD gene encodes a putative Ni ²⁺ permease whose carboxy-terminal region is a metal binding domain. The Co ²⁺ response system is composed of two divergently transcribed genes, corR and corT , mutants of which showed decreased Co ²⁺ tolerance. Additionally, corR mutants showed an absence of Co ²⁺ -dependent induction of corT , indicating that CorR is a transcriptional activator of corT . To our knowledge, CorR is the first Co ²⁺ -sensing transcription factor described. Our data suggest that this region of the Synechocystis sp. strain PCC 6803 genome is involved in sensing and homeostasis of Ni ²⁺ , Co ²⁺ , and Zn ²⁺ .