Comparative evaluation of fossil bone bioconsolidation via two endogenous bacterial strains: Bacillus subtilis and Sporosarcina pasteurii

Abstract

This research evaluates microbially induced calcium carbonate precipitation (MICP) generated by means of two endogenous bacterial strains inhabiting Titanochelon richardi (formerly Cheirogaster richardi) fossil bone remains; in this case, Bacillus subtilis and Sporosarcina pasteurii. Both bacterial strains were inoculated on different samples to study their possible effectiveness and to verify whether an improvement in the cohesion and mechanical strength of the fossil surface is achieved by the formation of a bioconsolidated carbonate matrix within the specimen. Treatment chemical compatibility was also considered as well as non-occurrence of noticeable changes in the main properties and appearance of the substrate. Several methods were used to analyse and compare samples before and after treatment and the benefits and limitations of both treatments, including ATP analysis, Field Emission Scanning Electron Microscopy, X-ray Diffraction, surface roughness analysis, pH and conductivity measurements, weight monitoring, water absorption tests, Vickers microindentation, peeling tape test and spectrophotometry. Results indicate that both strains, with some differences between them, significantly improved fossil hardness and cohesion by filling pores, valleys and fissures and by binding disaggregated particles with minimal impact on surface topography and appearance. Weight, pH and conductivity hardly changed, while porosity was reduced but not blocked. Overall, bioconsolidation with both strains proved to be effective and highly compatible with carbonate fossil bones, making it a feasible, suitable and alternative treatment for these substrates. Furthermore, bacterial-induced calcium carbonate precipitation is a safe and environmentally sustainable technique for consolidation treatments.