Decoding the role of hypothetical protein All3255 of Anabaena PCC7120 in heavy metal stress management in Escherichia coli

Cadmium is a non-essential toxic heavy metal for organisms, including plants and cyanobacteria. Cadmium resistance transporters involved in resistance of cells against various toxicants such as drugs and effluxes cytotoxic compounds from cells. However, cadmium resistance-associated protein (CadD) has never been reported from a diazotrophic cyanobacterium Anabaena sp. To test whether the hypothetical protein All3255 of Anabaena sp. PCC7120 a homolog of cadmium resistance-associated protein (CadD) involved in cadmium or heavy metal resistance or not, cloning and heterologous expression analysis of all3255 performed in Escherichia coli BL21 (DE3). Our results revealed that the strain transformed with pGEX-5X-2 + all3255 showed resistant towards not only to cadmium but also other heavy metals such as nickel, copper, zinc, lead and cobalt in addition to arsenic than those of transformed with empty vector (pGEX-5X-2). Furthermore, the results of metal accumulation analysis of these cells unveil a lower accumulation of tested heavy metals in all3255-overexpressing E. coli cells than those transformed with empty vector. This study strongly supports the role of All3255 of Anabaena sp. PCC7120 as a CadD efflux pump of heavy metals in E.coli.