Biodeterioration effects of the endolithic Bagliettoa sp. (lichenized verrucariaceae) on the limestones of persepolis, UNESCO world heritage site

This study examines the role played by the endolithic thallus of the lichen-forming fungi Bagliettoa sp., an apparently undescribed species, in the biodeterioration of Persepolis, a UNESCO World Heritage Site in Iran. This species produces abundant large reproductive bodies (perithecia) creating micropits with aesthetic impacts that persist even after the lichen is no longer present. The aim of this study was to gain insight into how these micropits develop and their effects on colonized limestone. By both light and electron microscopy, the various stages of micropit development were examined from the emergence of perithecia on the stone surface until their decay. The potential for other microorganisms to colonize these micropits and the surrounding stone was also assessed through metabarcoding analysis. Our results indicate that the formation and emergence of perithecia caused more pronounced structural damage to the limestone than reported biogeochemical processes attributed to the endolithic spread of symbiont cells within the stone. As the thallus and perithecium disintegrate, micropits fill with mineral fragments, while micrite and algal layers vanish. This eventually leads to the removal of up 0.5 mm of stone surface, leaving behind a surface marked by empty, shallow micropits. Bacterial colonies were observed at all defined stages, initially associated with the micrite layer and later with perithecium remnants. No specific signs of biodeterioration activity on the limestone could be attributed to these bacterial colonies. Metabarcoding results revealed a lower bacterial diversity in micropits with healthy perithecia and a greater abundance of cyanobacteria compared to empty micropits or those containing only perithecium remnants. However, no significant differences in bacterial community structure were detected across the different micropit stages, suggesting that new taxa rarely become established during micropit development. Our study provides new insight into the effects of endolithic lichens associated with perithecium micropit formation. Knowledge of this biodeterioration mechanism is essential for the design of preservation strategies for Persepolis and other sites featuring the dominance of these lichens.