Producti~n of a Novel Copper-Binding Ligand by Marine Synechococcus (Cyanobacteria) in Response to Toxic Concentrations of Copper

Marine Synechococcus spp. are extremely sensitive to copper toxicity. Some strains have been shown to produce high-affmity, extracellular ligands of unknown structure which form complexes with free cupric ion. They are also known to produce metaJlothioneins (MT) in response to cadmium and zinc stress. In the present study, marine Synechococcus PCC 73109 (Agmenel/um quadruplicatum BG-1) (Van Baal en) was exposed to three concentrations of CuSO 4 for various times. Size exclusion chromatography, atomic absorption spectrophotometry, and reverse phase HPLC were used to isolate an intracellular copper binding ligand oflow molecular weight ( < 6,500 Da). The ligand was detected after exposure to ~ 8 μM CuSO 4 for 2 hr in BG-11 medium. The intracellular ligand was characterized by electrospray mass spectrometry, amino acid analysis and a universal assay for siderophores. The ligand was not MT, phytochelatin or a siderophore. It is not a peptide but it contains lysine and an unidentified UV 254-absorbing constituent. This compound is a novel copper-binding ligand previously not reported in Synechococcus spp. Key Index Words: copper toxicity, intracellular copper binding ligand, lysinecontained ligand, marine Synechococcus, low molecular weight non-peptide