Identification and characterization of algae metallothioneins for use in heavy metals bioremediation.

BURDISSO, M.L.; PETRICH, J; PALACIOS, O; ALBALAT, R; CAPDEVILA, M.; DIEGO FABIAN GOMEZ CASATI; PAGANI, MARIA A.

Virtual

Congreso; LVII SAIB Meeting - XVI SAMIGE Meeting; 2021

SAIB - SAMIGE

Metallothioneins (MTs) constitute a large and heterogeneous superfamily of low molecular mass cytosolic proteins composed of about 30-100 amino acids. Its primary structure is characterized by a high content of cysteine residues (Cys) located in highly conserved CC, CxC and CxxC motifs. This characteristic allows these proteins a great ability to coordinate significant amounts of mono or divalent metal ions through metal-thiolate bonds, thus constituting metal clusters. MTs are usually the main primary response of organisms to an inadequate type/dose of heavy metals, operating by chelation and immobilization. In the case of algae, MTs from only two species have been found and characterized. It is strange that these proteins have not been identified in a greater number of algae, these species being highly resistant to metals, and with a great capacity to accumulate them. For this reason, in this work we used different bioinformatic approaches to uncover new algae MTs. Our objectives were to establish phylogenetic relationships between MTs from the different algae taxons and to characterize some of them for use in heavy metal bioremediation. We identified 124 potential MT sequences from algae: 26 from Chlorophytas, 51 from Rodophytas and 47 from Ochrophytas. The sequences of algal MTs are very heterogeneous. Most of the primary structures of MTs from Rhodophytas and Ochropytas contain Cys domains and intermediate linker regions devoid of these amino acids, similar to higher plants. However, the primary structures of Chlorophytas tend to contain Cys residues throughout the entire sequence or very short linkers. We are currently working on the characterization of four MTs. Two correspond to the brown macroalgae Ectocarpus siliculosus (EsilMT1 and EsilMT2), one to a red microalgae Galdieria sulphuraria (GsulMT) and one to a green microalgae Auxenochlorella protothecoides (AproMT). EsilMT1 has a primary structure similar to higher plants, whereas EsilMT2 has a shorter sequence with fewer Cys residues. GsulMT and AproMT consist of sequences with more than 30% Cys residues distributed throughout their sequences. Complementation assays in MT-deficient yeasts showed that the MTs conferred, to varying degrees, resistance to the presence of hydrogen peroxide, Zn, Cu, and Cd. When these MTs were expressed in E. coli, they also provided a better growth performance to the bacteria in high Zn, Cu and Cd media. The characterization by ICP-AES and ESI-MS of the MTs synthesized in E. coli showed that they have affinity for metals in different ways. We present here these algae MTs as promising tools for metal bioremediation, with the perspectives of expressing them heterologously in the wall of fast-growing algae, immobilizing this biomass in columns, and conducting adsorption studies for the removal of metal ions from aqueous solutions.