Cadmium-mediated resistance to metals and antibiotics in a cyanobacterium

Summary Cadmium-resistant strains of the cyanobacterium Nostoc calcicola were isolated through the step-wise transfer of the organism to higher levels of the metal. One of the Cd-resistant strains (Cd^r–10) showed cross-resistance to antibiotics like neomycin (1 g/ml), chloramphenicol (3 g/ml) but not to streptomycin. The Cd-resistant strain also tolerated elevated levels of metals such as zinc (20 ppm) and mercury (1 ppm). The stability of the metal-resistance required the presence of Cd²⁺ ions in the growth medium. It is suggested that metal resistance may also be determined by gene(s) on the antibiotic resistance plasmids in cyanobacteria.