Cell wall modification of the green algae Scenedesmus sp.

BURDISSO, M.L.; PETRICH, J; BAGNATO, C; DIEGO FABIAN GOMEZ CASATI; PAGANI M.A.

Virtual

Congreso; Reunión conjunta 2020 SAIB-SAMIGE; 2020

SAIB

Metallothioneins (MTs)constitute a large and heterogeneous superfamily of low molecular masscytosolic proteins composed of around 30-100 amino acids.Its primary structureis characterized by ahigh content of cysteine (Cys) residues located in highlyconserved CC, CxC and CxxC motifs. This characteristic allows these proteins a greatability to coordinate significant amounts of mono or divalent metal ionsthrough metal-thiolate bonds, thus constituting metal clusters. MTs are usuallythe main primary response of organisms to an inadequate type/dose of heavymetals, operating by chelation and immobilization.In addition to participate onmetal homeostasis and detoxification, they are also involved in a variety ofstress responses that are not limited to metal ions.In the case of algae,only four MTs sequences have been identified and characterized. One MT is from themarine brown macroalga Fucus vesiculosus, which has two cysteine-richregions (CxCxxxCxCxxxCxC) and an extra CCxCmotif. It was observed that this gene was induced inthe presence of high copper concentrations.The other three MTs described belongto the green seaweed Ulva compressa. They have similarity with mollusc MTs but not with brown or red algaeMTs, andthey were also induced by high copper concentration.In this work we used different bioinformatics approachesto uncover new algae MTs. Our objectives were to establish phylogeneticrelationships between MTs from the different algae taxons and to characterizesome of them for use in heavy metal bioremediation.We identified 16 MTsfrom green algae, 40 MTs from red algae, and 7 MTs from brown algae. We observedthat most MT primary structures from brown and red algae are similar to thoseof higher plants, with two Cys domains and an intermediate linker region devoidof these amino acids. Instead, the MTs sequences from green algae tend to containCys residues throughout the entire sequence, lacking a spacer linker region. We are working on the characterization of threepossible algae MTs. Two correspond to the brown macroalgae Ectocarpus siliculosus (EsilMT1 and 2), and one from the greenmicroalga Micromonas sp. EsilMT1 has a primary structure similar tohigher plants, whereas EsilMT2 and MMT1  have shorter sequences, with a single Cys-richdomain. Complementation assays in MT-deficient yeasts, showed that the three MTsconferred, to varying degrees, resistance to the presence of hydrogen peroxide,Cu and Cd. When these MTs were expressed in E.coli,they also provided a better growth performance to the bacteria in high Zn, Cuand Cd media. In conclusion, we present these algae MTs as promising tools formetal bioremediation, either expressed in their host species or in heterologousexpression in yeasts, bacteria or other rapid growing algae.