β-cyanoalanine production by marine bacteria on cyanide-free medium and its specific inhibitory activity toward cyanobacteria

Research studies of inhibitors of bacteria, fungi, and cultured cells have accumulated, and many effective drugs have appeared for clinical use. However, the number of reports of antimicroalgal compounds is relatively small, although these organisms cause such problems as blooms by cyanobacteria, red tide and the production of marine toxins by dinoflagellates, and biofilm formation on marine structures by diatoms. In particular, some bloom-forming cyanobacteria are known to produce toxic metabolites such as anatoxins (8) and microcystins (3). The mechanism by which the cyanobacteria form blooms remains to be investigated, but the threat and damage to human and animal life and to industry are serious. In the present study, we screened strains for antimicroalgal compounds against one cyanobacterium and three eukaryotic microalgae. A culture broth of each of 2,594 marine bacterial strains was examined in this screening, and among them, 37 strains were found to produce anticyanobacterial substances in the culture on marine broth 2216 (MB). Interestingly, no inhibitory activity toward the three eukaryotic microalgae tested was apparent in the broths of any of these bacterial strains. We purified the anticyanobacterial compound from C-979, which showed the highest anticyanobacterial activity. The chemical structure was determined for the compound, and the bioactivity profile was examined. Furthermore, we examined if the above-mentioned 37 strains produce the same anticyanobacterial compound that C-979 produces.