Alkyltrimethylammonium (ATMA) surfactants as cyanocides - Effects on photosynthesis and growth of cyanobacteria

Cyanobacteria and their toxins present potential hazard to consumers of water from lakes, reservoirs and rivers, thus their removal via water treatment or at the source, is essential. Here, we report that alkyltrimethylammonium (ATMA) surfactants, such as octadecyltrimethylammonium (ODTMA) bromide, act as cyanocides that efficiently inhibit photosynthesis and growth of cyanobacteria. Green algae were found less sensitive than cyanobacteria to ATMA compounds. Fluorescence measurements and microscopic observations demonstrated that cyanobacteria cells (Aphanizomenon or Microcystis) disintegrate and lose their metabolic activity (photosynthesis) upon exposure to ATMA bromides (estimated ED_50(1hr) ranged between 1.5 and 7 μM for ODTMA-Br or hexadecyltrimethylammonium (HDTMA) bromide). Other ATMA compounds, such as tetradecyltrimethylammonium (TDTMA) or dodecyltrimethylammonium (DDTMA) bromides had similar inhibitory effect but their toxicity to cyanobacteria (measured as ED_50(1hr) for photosynthetic efficiency) decreased, as the length of the alkyl chain decreased. All ATMA compounds used in this study showed lower toxicity to green algae than to cyanobacteria. A toxicity mechanism for ATMA cations is proposed, based on real time fluorescence signals and on alteration of cell ultra-structure revealed by electron microscopy. The present study sheds light on the toxic effect of ATMA surfactants on cyanobacteria and its potential application for controlling the occurrence of cyanobacterial bloom in lakes, reservoirs or rivers to secure the safety of drinking water and to mitigate and manage bloom events.