The Monomolecular-Layer Selective Adsorption of Amino Acids on Microbial Proto-Dolomite Induced by the Cyanobacterium Leptolyngbya Boryana

Abstract

Microbially mediated mineralization is widely recognized as a key pathway for proto-dolomite formation, with extracellular polymeric substances (EPS), especially amino acids, considered important mediators. Yet, the surface interactions between amino acids and proto-dolomite remain insufficiently characterized. In this study, we examined the adsorption behavior of four representative amino acids─aspartic acid (Asp), arginine (Arg), glycine (Gly), and proline (Pro)─on organic-free proto-dolomite (Cpdol) synthesized by the cyanobacterium Leptolyngbya boryana. Experiments were conducted across a range of pH and salinity conditions, and amino acid concentrations were measured using high-performance liquid chromatography. The adsorption data were well described by Langmuir isotherms, indicating a monomolecular-layer selective adsorption model. Adsorption capacity varied among amino acids (Asp > Gly > Pro > Arg) and showed a positive correlation with pH and a negative correlation with salinity. Based on density functional theory (DFT) calculations, the adsorption energies of the four amino acids were evaluated on seven crystal surfaces of proto-dolomite. The results indicate that surface complexation between carboxyl groups and surface metal ions is the primary mechanism driving adsorption. Under higher pH conditions, the deprotonated amino group can further enhance adsorption by lowering the adsorption energy. These findings suggest that, beyond acidic amino acids, surface complexation of various environmentally responsive amino acids may play an important role in regulating the early-stage formation of proto-dolomite in microbial environments.