Characterization of the Extracellular Polymeric Substances (EPS) of Virgibacillus strains capable of mediating the formation of high Mg-calcite and protodolomite

Abstract

The origin of dolomite -a common carbonate mineral- is the subject of an ongoing debate. It has been proposed that extracellular polymeric substances (EPS) excreted by microbes contain specific organic molecules that facilitate the incorporation of magnesium in the carbonate minerals. We characterized the EPS produced under different conditions by measuring total carbohydrate (TCHO), total protein (TP) content and by (FTIR) analysis. We report the formation of Mg-carbonates with a mol% Mg higher than 41% exclusively in association with EPS rich in carbohydrates (TCHO > than 75% of the total EPS mass). Moreover, FTIR analysis of these EPS revealed the presence of protein secondary structures (e.g., ?-sheets) known to favor mineral nucleation. These results suggest that some organic molecules with specific functional groups (e.g., carboxyl and hydroxyl groups) may be of key importance for overcoming the kinetic barriers that else prevent the incorporation of Mg into carbonate minerals, a crucial step for the formation of dolomite in natural environments.