Algicidal Activity of Streptomyces eurocidicus JXJ-0089 Metabolites and Their Effects on Microcystis Physiology

Copper sulfate (CuSO4) has been widely used as an algicide to control harmful cyanobacterial blooms (CyanoHABs) in freshwater lakes. However, there are increasing concerns about this application, due mainly to the general toxicity of CuSO4 to other aquatic species and its long-term persistence in the environment. This study reported the isolation and characterization of two natural algicidal compounds, i.e., tryptamine and tryptoline, from Streptomyces eurocidicus JXJ-0089. At a concentration of 5 μg/ml, both compounds showed higher algicidal efficiencies than CuSO4 on Microcystis sp. FACHB-905 and some other harmful cyanobacterial strains. Tryptamine and tryptoline treatments induced a degradation of chlorophyll and cell walls of cyanobacteria. These two compounds also significantly increased the intracellular oxidant content, i.e., superoxide anion radical (O2 (-)) and malondialdehyde (MDA), but reduced the activity of intracellular reductants, i.e., superoxide dismutase (SOD), of cyanobacteria. Moreover, tryptamine and tryptoline treatments significantly altered the internal and external contents of microcystin-LR (MC-LR), a common cyanotoxin. Like CuSO4, tryptamine and tryptoline led to releases of intracellular MC-LR from Microcystis, but with lower rates than CuSO4 Tryptamine and tryptoline (5 μg/ml) in cyanobacterial cultures were completely degraded within 8 days, while CuSO4 persisted for months. Overall, our results suggest that tryptamine and tryptoline could potentially serve as more efficient and environmentally friendly alternative algicides than CuSO4 in controlling harmful cyanobacterial blooms.