In-situ laboratory monitoring of cyanobacterial influence on calcite dissolution

Microbial interactions with mineral surfaces play a critical role in biogeochemical cycles, yet their dynamic coupling with mineral reactivity remains poorly constrained. Here, in-situ time-resolved monitoring of topographic evolution of the calcite-bacteria interface was performed using a fluid cell coupled to vertical scanning interferometry (VSI). The cyanobacterial strain Chroococcidiopsis thermalis PCC 7203 was inoculated onto polished and pre-etched calcite surfaces under conditions strongly undersaturated or closer to calcite saturation. The formation of localized topographic highs, produced by dissolution of surrounding material, was found to correlate with the residence time of attached cells at Ω = 0.0, but not at Ω = 0.3. Physiological tests suggested that the composition of the bulk fluid modulates microbial activity, thereby influencing interfacial pH, and in turn, calcite reactivity. Moreover, calcite reactivity was found to exert a stronger control on bacterial detachment dynamics than initial surface roughness or surface charge under the tested conditions. These findings emphasize the importance of microscale feedbacks between microbial colonization and mineral weathering, and demonstrate the potential of in-situ interferometric imaging for probing the dynamics of processes at microbe-mineral interfaces.