Microcystis aeruginosa in lichen biofilms: Linking ecological plasticity to mineral transformation

Lichens function as multi-kingdom biofilm systems that actively drive mineral transformation on stone substrates. In this study, eight lichen species collected from Eastern Anatolia (Türkiye) were analyzed to characterize their associated microbial communities and the underlying biochemical mechanisms of stone biodeterioration. From an initial pool of 185 microbial isolates, a representative subset of 55 taxa was molecularly identified, revealing a diverse consortium dominated by Bacillus, Pseudomonas, Fusarium, Aspergillus, and the cyanobacterium Microcystis aeruginosa. The detection of M. aeruginosa, a microbe typically found in freshwater environments, within terrestrial lichen thalli demonstrates pronounced ecological plasticity and identifies lichens as transitional microhabitats between aquatic and lithic environments. The process of biodeterioration is driven by a combination of organic acid production and the presence of extracellular polymeric substances (EPS), which together generate localized acidic microenvironments (pH values as low as 4.8). In particular, oxalic acid was found to mediate a stoichiometrically defined transformation of calcium carbonate according to the following reaction: Quantitative analysis via HPLC and ICP-MS confirmed a direct correlation between microbial acid titers and massive elemental mobilization (up to 19,958 ppm Ca). This mass-balanced pathway directly links microbial metabolism to mineral phase transformation and provides a mechanistic framework for understanding lichen-induced stone decay. The integration of microbial ecology with stoichiometric mineral transformation has advanced current understanding of biogeochemical weathering in cultural heritage materials.