Effects of Copper and pH on the Growth and Physiology of Desmodesmus sp. AARLG074

Abstract

Copper (Cu) is a heavy metal that is widely used in industry and as such wastewater from mining or industrial operations can contain high levels of Cu. Some aquatic algal species can tolerate and bioaccumulate Cu and so could play a key role in bioremediating and recovering Cu from polluted waterways. One such species is the green alga Desmodesmus sp. AARLG074. The aim of this study was to determine how Desmodesmus is able to tolerate large alterations in its external Cu and pH environment. Specifically, we set out to measure the variations in the Cu removal efficiency, growth, ultrastructure, and cellular metabolite content in the algal cells that are associated with Cu exposure and acidity. The results showed that Desmodesmus could remove up to 80% of the copper presented in Jaworski’s medium after 30 min exposure. There was a decrease in the ability of Cu removal at pH 4 compared to pH 6 indicating both pH and Cu concentration affected the efficiency of Cu removal. Furthermore, Cu had an adverse effect on algal growth and caused ultrastructural changes. Metabolite fingerprinting (FT-IR and GC-MS) revealed that the polysaccharide and amino acid content were the main metabolites affected under acid and Cu exposure. Fructose, lactose and sorbose contents significantly decreased under both acidic and Cu conditions, whilst glycerol and melezitose contents significantly increased at pH 4. The pathway analysis showed that pH had the highest impact score on alanine, aspartate and glutamate metabolism whereas Cu had the highest impact on arginine and proline metabolism. Notably both Cu and pH had impact on glutathione and galactose metabolism.

Phenotypic changes in microalgae at acidic pH mediate their tolerance to higher concentrations of transition metals

“…However, during the acclimation process, carbohydrate, protein, and lipid accumulation was modified in cells growing at acid pH compared to pH 6.5. Buayam et al. (2019) observed a significant decrease in synthesis of polysaccharides and amino acids in Desmodesmus sp.…”

Copper Effect on Microalgae: Toxicity and Bioremediation Strategies

“…In another study, performed using one species of the genus Desmodesmus as testorganism, variations in the Cu removal efficiency, growth, ultrastructure and cellular metabolite content associated with Cu exposure as well as different pH were assessed [65]. That species was found to be able to grow in media supplemented with Cu, with a pHdependent adsorption efficiency of the metal.…”

“…That species was found to be able to grow in media supplemented with Cu, with a pHdependent adsorption efficiency of the metal. Metabolic alterations associated to Cu exposure and medium acidity mostly affected sugars and amino acids content [65].…”

Physiological responses to pH in the freshwater microalga Limnomonas gaiensis

“…Thus, the acclimation of strains to acid pH could alleviate metal toxicity [24]. Part of this reaction is explained by significant modifications in the microalgal metabolism, leading to the reduction of key polysaccharides and amino acids contents [25]. At pH 4, glycerol production is also promoted, impacting cell membrane permeability [25].…”

“…Part of this reaction is explained by significant modifications in the microalgal metabolism, leading to the reduction of key polysaccharides and amino acids contents [25]. At pH 4, glycerol production is also promoted, impacting cell membrane permeability [25]. Effect on membrane permeability was also demonstrated at higher pH (pH 5.5) through the decrease of lipophilic complexes uptake in acidic freshwater microalgae [26].…”