Investigating the role of the cell wall in the susceptibility of freshwater phytoplankton to novel chemical stressors

Emerging chemicals can impact aquatic organisms and ecosystems in unique and novel ways.  However, more information about the mechanisms of toxicity to freshwater organisms is necessary before an accurate assessment of the potential environmental impacts of these chemicals can be made.  Ionic liquids (ILs) have been shown to have wide-ranging toxicity to freshwater algae, and differences in algal cell walls have been posed as one possible explanation for this observed variation.  We used wild-type and mutant (lacking a cell wall) strains of the freshwater phytoplanktor Chlamydomonas reinhardtii to examine the role of the cell wall in IL susceptibility using 96h standard toxicity bioassays.  While the sensitivity of both strains to a suite of six structurally different ILs was wide-ranging (EC_{50 wild-type} = 18 to 5203 mg L^-1, EC_{50 mutant} = 9 to 1250 mg L^-1), our results suggest that the cell wall plays a role in the susceptibility of C. reinhardtii to ILs. Furthermore, the base structure of the IL appears to change the efficacy of the cell wall in mitigating the toxic effects of ILs.  The results of this study have important implications for predicting the impacts of ILs in aquatic ecosystems and extrapolating these effects across freshwater organisms.