Insights into the influence of reinforcing iron bars corrosion on historical buildings: Towards optimizing limestone performance Jroundi, Fadwa Povedano Priego, Cristina Merroun, Mohamed Larbi González Muñoz, María Teresa Rodríguez Navarro, Carlos Manuel Bacterial diversity Cultural heritage Framboidal pyrite We acknowledge funding by the Spanish Government grant PID2021-125305NB-I00 funded by MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe, Junta de Andalucía research groups RNM-179, BIO-103, and grant P20_00675, University of Granada, Unidad Científica de Excelencia UCE-PP2016-05, and the Junta de Andalucía through Proyecto de Excelencia RNM-3493. We thank J. Vicente Navarro for the help with SEM analyses and J. Ramos for the photographs of the pinnacles. Scanning electron microscopy analyses were performed at the Centro de Instrumentación Científica of the University of Granada and the Instituto del Patrimonio Histórico Español. Funding for open access charge: Universidad de Granada / CBUA. Iron bar corrosion in ancient limestone buildings and sculptures causes severe damage, yet the underlying mechanisms and microbial contributions remain poorly understood. This study examined heavily deteriorated pinnacles from a 16th-century building in Granada, Spain, combining mineralogical, compositional, textural and metagenomic analyses. A highly diverse microbial community was identified, including iron-oxidizing [e.g., Massilia (4.59 %) and Ralstonia (<1 %)], sulfate-reducing [SRB, e.g., Desulfovibrio (<1 %) and Clostridium (1.43 %)], and nitrate-reducing [e.g., Pseudomonas (22.93 %) and Staphylococcus (2.53 %)] bacteria. The degradation process initiates by (bio)corrosion of embedded iron bars, followed by SRB-induced in situ (authigenic) framboidal pyrite formation under anoxic conditions, in the presence of sulfates from pollution-derived gypsum. Pyrite is then bacterially oxidized into goethite pseudomorphs under fluctuating aerobic and anoxic conditions, triggering a localized acid mine drainage-like process. This results in significant limestone dissolution and structural instability. These findings highlight the crucial role of microbial activity and reveal previously unrecognized pathways in stone degradation. Understanding such processes offer valuable insights for improving conservation strategies of cultural heritage. 2025-07-03T10:15:14Z 2025-07-03T10:15:14Z 2025-06-16 journal article F. Jroundi et al. Journal of Building Engineering , 2025, 111, 113203. https://doi.org/10.1016/j.jobe.2025.113203 https://hdl.handle.net/10481/105056 10.1016/j.jobe.2025.113203 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Elsevier