The role of three-tandem Pho Boxes in the control of the C-P lyase operon in a thermophilic cyanobacterium

Cyanobacteria have an inherited advantage in phosphonate phytoremediation. However, studies on phosphonate metabolism in cyanobacteria are rare and mostly focus on physiology and ecology. Here, C-P lyase gene cluster regulation in an undomesticated thermophilic Synechococcus OS-B′ was examined in Synechocystis sp. PCC6803, a unicellular cyanobacterial model. Phylogenetic and cluster synteny analysis of C-P lyase genes revealed a closer relationship between Syn OS-B′ and Thermus thermophilus, than with other cyanobacteria. Pho boxes were identified in the 5′-end-flanking region of the C-P lyase gene cluster, through which the downstream gene expression was regulated in a phosphate concentration-dependent manner. Unexpectedly, the phosphate concentration that thoroughly inhibited Pho boxes was almost two orders of magnitude higher than that of any natural or anthropogenic wastewater reported so far. The Pho boxes mediated regulation was achieved through the Pho regulon two-component system, and the absence of either SphS or SphR ablated the cell's ability to sense ambient phosphate changes. The three tandems of Pho boxes maintained inequivalent roles, of which the third tandem was not essential; however, it played a role in adjusting Pho boxes response in both positive and negative manner under phosphorus limitation.