Evaluating the efficacy of probiotic bacterial strain Lactobacillus plantarum for inhibition of fungal strains associated with historical manuscript deterioration: An experimental study

The aim of this study is to develop safe biological methods for controlling fungal deterioration of historical manuscripts. Therefore, fifteen fungal isolates were obtained from paper sheets and leather skins of a deteriorated historical manuscript (dated back to the 13th century). Those isolates were identified using both traditional methods and ITS-sequencing analysis. Aspergillus niger accounted for seven strains, Penicillium citrinum for one strain, Aspergillus flavus for three, Aspergillus fumigatus for one, Aspergillus nidulans for one, and Penicillium chrysogenum for two of the fungal strains that were obtained. The ability of fungal strains for the secretion of cellulase, amylase, gelatinase, and pectinase as hydrolytic enzymes was evaluated. The capability of the probiotic-bacterial strain Lactobacillus plantarum DSM 20174 for inhibition of fungal strains that cause severe deterioration was studied using ethyl acetate-extract. The metabolic profile of the ethyl acetate-extract showed the presence of both high- and low-molecular-weight active compounds as revealed by GC-MS analysis. The safe dose to prevent fungal growth was determined by testing the ethyl acetate extract's biocompatibility against Wi38 and HFB4 as normal cell lines. The extract was found to have a concentration-dependent cytotoxic impact on Wi38 and HFB4, with IC₅₀ values of 416 ± 4.5 and 349.7 ± 5.9 μg mL⁻¹, respectively. It was suggested that 100 μg mL⁻¹ as a safe concentration could be used for paper preservation. Whatman filter paper treated with ethyl acetate extract was used to cultivate the fungal strain Penicillium citrinum AX2. According to data analysis, fungal inhibition measurement, SEM, ATR-FT-IR, XRD, color change measurement, and mechanical property assessment, the recommended concentration of ethyl acetate extract was adequate to protect paper inoculated with the highest enzymatic producer fungi, P. citrinum AX2.