Role of Fungi in the Formation of Patinas on Feilaifeng Limestone, China.

Feilaifeng is a cultural heritage site that contains unique Buddhist statues which date back to the Five Dynasties period (907 AD-960 AD). The site was inscribed on world heritage list by UNESCO in 2011. Various patinas, which may be caused by fungi, have covered the surface of the limestone and have severely diminished the esthetic value of the statues and altered the limestone structure. Culture-dependent method was used to isolate and identify the fungi. After incubation on modified B4 medium, the calcifying fungi were identified by optical microscopy and scanning electron microscopy combined with X-ray energy-dispersive analysis. Aspergillus, Penicillium, and Colletotrichum were observed as the biomineralizing fungi. X-ray diffraction showed that the patina consisted of calcite (CaCO3), but the crystals synthesized by the identified fungi were whewellite (CaC2O4·H2O) for Aspergillus and Penicillium, and vaterite (CaCO3) for Colletotrichum. In addition, the metabolites of Colletotrichum suppressed the transformation of vaterite to calcite, but Mg2+ could inhibit the function of the metabolites. The different crystal form between the patina and the products of fungi may suggest two different pathways of patina formation and provide important reference data for studies of the mechanisms of biomineralization, cleaning of the patina, and protection of the Feilaifeng statues.