Rare earths stick to rare cyanobacteria: Future potential for bioremediation and recovery of rare earth elements

Michael Paper; Max Koch; Patrick Jung; Michael Lakatos; Tom Nilges; Thomas B Brück

doi:10.3389/fbioe.2023.1130939

Rare earths stick to rare cyanobacteria: Future potential for bioremediation and recovery of rare earth elements

Front Bioeng Biotechnol. 2023 Feb 28:11:1130939. doi: 10.3389/fbioe.2023.1130939. eCollection 2023.

Authors

Michael Paper¹, Max Koch², Patrick Jung³, Michael Lakatos³, Tom Nilges², Thomas B Brück^{1

4}

Affiliations

¹ Werner Siemens-Chair of Synthetic Biotechnology, School of Natural Sciences, Department of Chemistry, Technical University of Munich, Garching, Germany.
² Synthesis and Characterization of Innovative Materials, School of Natural Sciences, Department of Chemistry, Technical University of Munich, Garching, Germany.
³ Integrative Biotechnology, University of Applied Sciences Kaiserslautern, Pirmasens, Germany.
⁴ TUM AlgaeTec Center, Ludwig Bölkow Campus, Department of Aerospace and Geodesy, Taufkirchen, Germany.

Abstract

Biosorption of metal ions by phototrophic microorganisms is regarded as a sustainable and alternative method for bioremediation and metal recovery. In this study, 12 cyanobacterial strains, including 7 terrestrial and 5 aquatic cyanobacteria, covering a broad phylogenetic diversity were investigated for their potential application in the enrichment of rare earth elements through biosorption. A screening for the maximum adsorption capacity of cerium, neodymium, terbium, and lanthanum was conducted in which Nostoc sp. 20.02 showed the highest adsorption capacity with 84.2-91.5 mg g^-1. Additionally, Synechococcus elongatus UTEX 2973, Calothrix brevissima SAG 34.79, Desmonostoc muscorum 90.03, and Komarekiella sp. 89.12 were promising candidate strains, with maximum adsorption capacities of 69.5-83.4 mg g^-1, 68.6-83.5 mg g^-1, 44.7-70.6 mg g^-1, and 47.2-67.1 mg g^-1 respectively. Experiments with cerium on adsorption properties of the five highest metal adsorbing strains displayed fast adsorption kinetics and a strong influence of the pH value on metal uptake, with an optimum at pH 5 to 6. Studies on binding specificity with mixed-metal solutions strongly indicated an ion-exchange mechanism in which Na⁺, K⁺, Mg²⁺, and Ca²⁺ ions are replaced by other metal cations during the biosorption process. Depending on the cyanobacterial strain, FT-IR analysis indicated the involvement different functional groups like hydroxyl and carboxyl groups during the adsorption process. Overall, the application of cyanobacteria as biosorbent in bioremediation and recovery of rare earth elements is a promising method for the development of an industrial process and has to be further optimized and adjusted regarding metal-containing wastewater and adsorption efficiency by cyanobacterial biomass.

Keywords: biosorption; cyanobacteria; ion exchange; mechanism; rare earth elements.

Grants and funding

This project was funded by the Bavarian State Ministry of the Environment and Consumer Protection within the framework of the ForCycle II Project Group. ML was supported by the Ministry of Science and Health Rhineland-Palatinate (PhytoBioTech, 724–0116#2021, 004–1501 15405), by the Federal Ministry of Education and Research (W2V-Strategy2Value, 03WIR4502A & Technology2Value 03WIR4504B) as well as by EU-HORIZON (Waste2BioComp ID: 101058654). PJ was funded by the German Research Council (DFG; Grit Life; JU 3228, 1–1).