Background and Objectives: The present study was to evaluate the microbial diversity inhabiting biodeteriorated precious manuscripts of the Holy Quran placed in one of the repositories of the Library of Astan Quds Razavi (AQR), and its relation to the air microbial diversity. Materials and Methods: Three non-invasive sampling methods, culture-based techniques, and molecular identification were used to investigate the microorganisms involved in deterioration. To investigate the air microbial quality and its role in the destruction of the repository objects, air samples were taken from six different points inside the repository. Biomodeling studies were designed to verify the impact of microbial isolates. Results: 14 fungal isolates were obtained from three deteriorated ancient Quran manuscripts. The most frequently isolated fungi from the different substrates were Aspergillus spp. and Penicillium spp. In the air, the prevalence across fungal genera was rather uniform. 30 species of the identified bacteria were collected from three manuscripts. The results obtained in the present study showed that the bacterial species from different genera belonged to three phyla: Proteobacteria (n = 2), Actinobacteria (n = 4), and Firmicutes (n = 24). The paper strips were artificially colonized by Aspergillus sp., Penicillium chrysogenum, and Talaromyces diversus producing spots which were visible to the naked eye. In the scanning electron microscopy images, the colonization of the selected organism was observed. Conclusion: The characteristics of paper inoculated artificially with these microbial isolates confirmed their deteriorating effects. Based on molecular identification, the similarity of fungal and bacterial species isolated from both substrates and air samples suggest the direct relationship between microorganisms from the air and those isolated from the manuscripts.

Keywords