Abstract
Argimicin A is a potent anti-cyanobacterial compound produced by one of algae-lysing bacteria, Sphingomonas sp. M-17. Since the compound seemed to exhibit selective activities against cyanobacteria and such selectivity were considered to be quite rare, the mode of action of argimicin A was investigated. Argimicin A showed a unique delayed action, i.e., the cyanobacterial cell division continued until at least 36 hours treatment even though the decrement of oxygen evolution has been observed at 24 hours treatment. The compound is concluded to be a photosynthetic inhibitor which interrupts electron transport chain prior to photosystem II. From the preliminary fluorescent spectrum of argimicin A treated cyanobacterial cells, the site of action was speculated to be photo energy transfer from a cyanobacterial specific complex of accessory protein pigments, phycobilisome, to photosystem II.