Construction of a marine cyanobacterial strain with increased heavy metal ion tolerance by introducing exogenic metallothionein gene.

A marine cyanobacterial strain with enhanced heavy metal ion tolerance was constructed by introducing an exogenous cyanobacterial metallothionein gene, smtA, from a freshwater unicellular cyanobacterium, Synechococcus sp. PCC 7942. An expression vector harboring the c-phycocyanin (cpc) promoter and cpc N-terminal region was constructed and smtA was inserted into its multiple cloning site. The marine cyanobacterium, Synechococcus sp. NKBG 15041c, was highly sensitive to the heavy metal ions present in the medium. However, the recombinant marine cyanobacteria harboring the expression vector with smtA could grow even in the presence of 4 µM of CdCl2, at which concentration the wild-type strain did not grow.