Argimicin A

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.

To improve the efficiency of screening for anti-Microcystis compounds, we planned to use algae-lysing bacteria that kill the organisms of water blooms. A two step-screening process was carried out, i.e., the screening of algae-lysing bacteria and the selection of anti-Microcystis producers from the bacteria. Sources for the isolation of the bacteria were a co-cultivated fluid of a water sample with axenic Microcystis viridis, a water sample collected in a water bloom season, and a water bloom sample. The water bloom sample was the best source for the isolation of the algae-lysing bacteria and such bacteria were shown to exhibit potent activity. Seventeen strains out of 20 isolated algae-lysing bacteria produced anti-Microcystis activities, and one of the principles was the previously reported argimicin A. These results indicate that algae-lysing bacteria in water blooms may be good sources for potent and selective anticyanobacterial compounds.