Toxicological effects and mechanisms of lithium on growth, photosynthesis and antioxidant system in the freshwater microalga Chromochloris zofingiensis

Abstract

The growing prevalence of lithium (Li) batteries has drawn public attention to Li as an emerging pollutant. The present study investigates the toxicity of Li⁺ on Chromochloris zofingiensis, examining physiological, biochemical and omics aspects. Results reveal hormesis effects of Li⁺ on C. zofingiensis growth. At Li⁺ concentrations below 5 mg L^-1, Li⁺ can enhance chlorophyll content, mitochondrial activity, and antioxidant capacity, leading to increased dry cell weight and cell number. Conversely, when it exceeded 10 mg L^-1, Li⁺ can reduce chlorophyll content, induce oxidative stress, and disrupt chloroplast and mitochondria structure and function, ultimately impeding cell growth. In addition, under 50 mg L^-1 Li⁺ stress, microalgae optimize absorbed light energy use (increasing Fv/Fm and E TR ) and respond to stress by up-regulating genes in starch and lipid biosynthesis pathways, promoting the accumulation of storage components. Weighted gene co-expression network analysis indicates that peptidylprolyl cis/trans isomerase, GTPase and L-ascorbate oxidase might be the key regulators in response to Li⁺ stress. This research marks the toxic effects and molecular mechanisms of Li⁺ on freshwater microalga, which would improve our understanding of Li's toxicology and contributing to the establishment of Li pollution standards.

Keywords: Hormesis effects; Lithium; Microalgae; Photosynthesis; Reactive oxygen species.