Molecular Imaging of Microbially Induced Corrosion of Synthetic Archeological Glasses by a Rhizosphere Bacterium

Microbially induced corrosion (MIC) focuses on the degradation of solid materials, such as glass or metal. Soil microbes are often associated with the corrosion of foreign objects in the rhizosphere. <i>Paenibacillus polymyxa</i> SCE2, a facultative anaerobic bacterium in soil, is of the same genus as bacteria found near nuclear waste disposal sites. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used for imaging surface changes induced by <i>P. polymyxa</i> SCE2 cultured on two synthetic glass coupons to represent natural analogs of materials that were studied in relation to the vitrification of nuclear waste. Multimodal imaging was used to verify bacterial coverage across the glass surface after long-term growth. ToF-SIMS spectral analysis showed detection of glass component ions, such as silicon oxide <i>(m</i>/<i>z</i>^<i>-</i> 59.96 SiO₂^-) and aluminum oxide (<i>m</i>/<i>z</i>^<i>-</i> 101.95 Al₂O₃^-), and biofilm's extracellular polymeric substance (EPS) components, such as pentadecanoic acid (<i>m</i>/<i>z</i>^<i>-</i> 241.22 C₁₅H₂₉O₂^-) and sterol lipids (<i>m</i>/<i>z</i>^<i>-</i> 311.16 C₂₀H₂₃O₃^-). ToF-SIMS spectral, imaging, and depth profiling analyses showed that the glass rich in silica and other light elements ("granite glass") had more "corrosion related" peaks than the glass that was less silica-rich and contained more iron ("dike glass"). These surface and interface compositional and spatial differences observed in the mass spectra and imaging were attributed to bacterial metabolism and an electron transfer mechanism influenced by morphological and compositional differences between the two types of glasses. ToF-SIMS is effective in studying microbial effects, bringing new molecular insights into MIC in a broader context of materials degradation.