Bacillus subtilis-mediated weathering of basalt revealed through sporulation

Silicate rock weathering is a naturally occurring process that provides a long-term sink for atmospheric CO2, but its natural rates are too slow on human-relevant timescales to offset anthropogenic emissions. Microbial activity offers a potential mechanism for accelerating silicate mineral dissolution and subsequent CO2 drawdown. Here, we investigated the role of Bacillus subtilis strains MP1 and MP2 in the weathering of basalt, a cation-bearing, silicate-rich rock. Incubation of basalt with MP1 or MP2 resulted in significantly increased levels of soluble calcium compared to uninoculated, abiotic controls. In addition to calcium, we demonstrated that other metals released during basalt weathering can efficiently trigger sporulation. Because sporulation is known to require cations including Ca2+, Fe2/3+, and Mn2+, this physiological response could be used as an additional proxy for monitoring and assessing silicate weathering in in vitro systems. Scanning electron microscopy revealed feldspar twinning features on basalt surfaces following microbial treatment, providing concrete evidence of silicate rock weathering; these micrographs also identified numerous ovoid cell structures, indicating the presence of bacterial spores at the mineral surface. Together, these findings establish MP1 and MP2 as active agents of basalt weathering and highlight Bacillus sporulation as a potential biosensor for silicate dissolution. By linking microbial physiology with geochemical processes, our results highlight how strain-specific interactions with rock compositions could inform silicate weathering strategies for carbon dioxide removal (CDR), including Enhanced Weathering (EW) and Microbial Carbon Dioxide Mineralization (MCM).