Effects of tryptamine on growth, ultrastructure, and oxidative stress of cyanobacteria and microalgae cultures

Tryptamine was screened for selective antialgal activity against different cyanobacteria and eukaryotic microalgae. In a rapid 96-well microplate bioassay cultures were exposed to tryptamine concentrations from 0.625 to 20 lg ml-1 and growth was estimated by daily optical measurements over a 216 h period. Inhibitory concentrations (IC50216h) obtained from the sigmoidal inhibition curves showed that tryptamine prevents the growth of most cyanobacteria and eukaryotic microalgae at similar concentrations. However, most of the eukaryotic algae recovered growth after being transferred to new tryptamine-free culture media, while most cyanobacteria showed no growth recovery. Microscopical examination of exposed cells showed no major effects of tryptamine on eukaryotic ultrastructure but showed major-induced alterations on cyanobacteria (disorganization of thylakoid membranes, intratylakoidal vacuolization, increased cytoplasmatic granules, and cell lysis). Biochemical analyses performed on Aphanizomenon gracile (cyanobacteria) and Ankistrodesmus falcatus (chlorophyceae) showed that tryptamine induces an increase in H2O2 production in both cultures. Although no significant changes in catalase activity were detected, both cultures showed an increase in ascorbate peroxidase activity following tryptamine exposure treatments. Interestingly, lipid peroxidation was found to increase only in A. gracile, suggesting that the cellular defence mechanisms triggered by this cyanobacterium were less efficient than the ones triggered by A. falcatus for the removal of reactive oxygen species (ROS). Strong lipid peroxidation in cyanobacteria might lead to irreversible membrane damages which probably prevent these organisms to recover growth after tryptamine exposure. On the contrary, the eukaryotic alga seems to respond quite effectively to tryptamine induced oxidative stress and this would explain the capacity for this organism to recover growth after being exposed to tryptamine.