| Virginia
Journal of Science.
2001. Vol 52 (4) : 259-272 |
| Production
of a Novel Copper-binding Ligand by Marine Synechococcus (Cyanobacteria) in
Response to Toxic Concentrations of Copper Arunsri C Brown and Andrew S Gordon, Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529-0266 ABSTRACT
Marine Synechococcus
spp. are extremely sensitive to copper toxicity. Some strains
have been shown to produce high-affinity, extracellular ligands of
unknown structure which form complexes with free cupric ion. They
are also known to produce metallothioneins (MT) in response to cadmium
and zinc stress. In the present study, marine Synechococcus PCC 73109 (Agmenellum quadruplicatum BG-1)
(Van Baalen) was exposed to three concentrations of CuSO4
for various times. Size exclusion chromatography, atomic
absorption spectrophotometry, and reverse phase HPLC were used to
isolate an intracellular copper binding ligand of low molecular weight
(< 6,500 Da). The ligand was detected after exposure
to 8 M CuSO4 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, lysine-contained ligand, marine Synechococcus, low molecular weight non-peptide ligand. Abbreviations: FPLC, Fast Protein Liquid Chromatography; MT, Metallothionein; OD450, Optical density at 450 nm; smt, Synechococcus metallothionein encoded gene. |