Abstract

Cyanobacteria are prokaryotic algae found in oceans and freshwaters worldwide. These organisms are important primary producers in aquatic ecosystems because they can provide essential food for grazers and herbivores. In this study, the effects of a functionalized ionic liquid [1-(2’-hydroxylethyl)-3-methylimidazolium chloride (HOEtMIMCl)] on growth and antioxidant enzymes of a freshwater cyanobacterium Synechococcus sp. PCC7942 were compared and evaluated using 96 h growth tests in a batch-culture system. The growth of Synechococcus sp. PCC7942 was not obviously inhibited by HOEtMIMCl, which indicates that Synechococcus sp. PCC7942 is not sensitive to HOEtMIMCl, and HOEtMIMCl is to some extent an “environmentally benign” solvent. However, remarkable physiological and biochemical responses, especially for antioxidant enzymes, occurred in the HOEtMIMCl treatments. HOEtMIMCl increased the soluble protein content, and enhanced the Superoxide Dismutase (SOD), peroxidase (POD) and catalase (CAT) activities at low concentrations, but inhibited them at high concentrations. However, malondialdehyde (MDA) content in the cyanobacterium rose significantly with increasing the HOEtMIMCl concentration. These observations indicated that although HOEtMIMCl did not inhibit the growth of Synechococcus sp. PCC7942, it would cause significant physiological and biochemical responses in the microalgal cells. Thus, we suggest that it is necessary to evaluate the toxicity of ionic liquids (ILs) before their release into the natural environment in order to predict their impact, avoiding irreparable damages.

Key words: Functionalized ionic liquid, Synechococcus sp., 1-(2’-hydroxylethyl)-3-methylimidazolium chloride (HOEtMIMCl), antioxidant enzymes, malondialdehyde (MDA).