Methylmercury Accumulation and Toxicity to Cyanobacteria: Implications of Extracellural Polymeric Substances and Growth Properties

Abstract

This investigation examines how extracellular polymeric substances (EPSs) and environmental factors influence the bioaccumulation of monomethylmercury (MMeHg) using a culture of Microcystis aeruginosa, which dominates eutrophic reservoir populations. The identified EPSs were classified as carbohydrates and proteins. Evaluation of the bioaccumulation of MMeHg in cells by multiple regression analysis reveals that the concentration of EPSs in filtrate, the initial concentration of MMeHg in media, and the age of the culture significantly affected the amount of accumulation of MMeHg. Based on the composition profiles, the concentrations of soluble carbohydrates were significantly higher in the cells with bioaccumulated MMeHg than in the control ones. Preliminary results based on SEM‐map investigations suggest that most of the MMeHg accumulated in the cytoplasm (intracellular). Additionally, the effective concentrations (EC50) of MMeHg that inhibit the growth of M. aeruginosa were 5.1 to 7.8 μg/L in the logarithmic phase and 2.5 to 4.6 μg/L in the stationary phase.

Role of phytoplankton in aquatic mercury speciation and transformations

“…The role of phytoplankton (algae and cyanobacteria) in Hg cycling (i. e., alteration of Hg redox state, Hg scavenging, the potential for methylation), as well as the description of the cellular and molecular targets involved in the toxicity of Hg in phototrophs, were thoroughly discussed previously Poulain 2014, Beauvais-Flück et al 2018). Hg bioavailability to phytoplankton (Dranguet et al 2014 and its toxicity to primary producers were also reviewed (Nuzzi 1972, Wu and Wang 2011, Chen et al 2014, Dranguet et al 2014, Beauvais-Flück et al 2017, Beauvais-Flück et al 2018. In this context, the importance of phytoplankton in aquatic mercury transformations was always questioned but never systematically addressed.…”