Microbial biofilms promote biomineralization and reduce leaf decay under controlled ionic conditions

Microbial biofilms are complex communities embedded in a self-produced extracellular polymeric substance (EPS) matrix that can influence both decomposition and mineral formation on organic substrates. While biofilms are often associated with tissue degradation, they may also contribute to preservation processes through microbially mediated biomineralization. In this study, we examined microbial community dynamics within leaf-associated biofilms and experimentally tested how selected metals and minerals influence the decay of biofilm-covered leaves under controlled laboratory conditions. Reconstructed microbial consortia derived from decaying leaves were exposed to varying ionic conditions to assess their effects on mineral precipitation and tissue degradation. Biofilm-forming communities combined with elevated Ca²⁺ concentrations promoted mineral formation on leaf surfaces and significantly reduced degradation, as confirmed by chlorophyll retention measurements. The biofilm-forming capacity of representative isolates was validated using a crystal violet assay. Heavy metals produced variable effects depending on the microbial community present, highlighting the importance of metal-microbe interactions in decay processes. In addition, the iron-reducing bacterium Shewanella promoted the precipitation of diverse iron minerals on leaf substrates. These findings demonstrate that microbial biofilms can create localized microenvironments favourable for biomineralization and may contribute to early stages of leaf preservation in natural depositional environments.