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Project Progress

Mineralogical Biosignatures Formed at and near the Cell-solution Interface (dm)

The primary goal of this project is to learn how microbial metabolism and metal ion-polymer interactions lead to production of novel assemblages interpretable as biosignatures. The first focus of our research has been development of laboratory biomineralization systems that simulate reactions at hydrophobic-hydrophilic interfaces. Our experimental design involves assembly of functionalized surfaces at boundaries between organic and aqueous solutions and their mineralization by iron oxyhydroxide, iron silicate, and iron phosphate minerals. The goals of this work are to develop an understanding of how organized polymers template nanocrystal particle growth. We have conducted experiments using alginic acids that resulted in extensive mineralization of oriented assemblies of nanoparticles, simulating biosignatures associated with neutrophilic iron-oxidizing bacteria. Using DADMAC, a spiral-shaped polymer that carries positively charged N-containing groups, we have induced mineralization of tubes and produced biomimetic iron silicate phases.

The second goal involves study of the structure, microstructure, form, and organization of nanoparticles of metal sulfides and oxides formed extracellularly as the result of enzyme-mediated redox reactions. We have documented extremely small (< 2 nm particles) generated through bacterial iron oxidation and uranium and sulfate reduction. Under some conditions, the < 2 nm particles aggregate to form larger crystals that assemble into novel morphologies predicted using the Debye-Smoluchowski equation. The oriented aggregation-based crystal growth pathway also leads to generation of biomaterials containing point, line, and planar (twin) defects. Understanding of the evolution of these highly reactive nanomaterials over time, a topic to be studied in the future, is critical to evaluation of the fate of biosignatures. NASA funding has allowed incorporation of a biosignature component in the studies of several students whose primary support is provided by other projects with other goals.