Diversity And Discoloration Simulation Test Analysis Of Bacteria Isolated From Aerosol And Murals In Mogao Caves

In order to illuminate the groups of microorganisms on the surface of mural paintings and within the air around paintings, and to evaluate the degree of mural painting discoloration induced by microorganism, air samples and mural samples were collected from the Mogao Caves. Microorganisms in these samples were incubated under 37℃ for 48 hours. Different bacteria were separated by spreading amplified samples on LB medium after dilution. Morphological characteristics were recorded and primary classification is implemented. Further identification of different bacteria was done by:amplify rRNA gene, pick out PCR products according to the fingerprint of double enzyme digestion, cloning and sequencing, DNA sequences were blasted on NCBI database. Separated pure bacteria were inoculated into 0.25%, 0.5%,1.0%,2.0%miniumite LB liquid media and 0.05%、0.2%、0.8% and 3.2% iron oxide red LB liquid media, and then, incubated at 37℃,150 rpm for 20 days. Chroma of pigment LB media of different days was recorded via colorimeter. Calculating difference value between chromas of different days’pigmental media.About 33 strains were isolated from airborne particles, which could be divided into 3 phylum, including Actinobacteria, Firmicutes and Proteobacteria. A total of 15 families and 20 different genera was researched corresponding to the GenBank data. They were Acetobacteraceae, Bacillaceae, Microbacteriaceae, Micrococcaceae, Oxalobacteraceae, Paenibacillaceae and so on. All of the strains charactersized into 20 genera, such as Acinetobacter, Micrococcus, Arthrobacter, Bacillus, Brevibacterium, Brevundimonas and Exignobacterium, of which the most common genera were Bacillus and Micrococcus.In mural samples, a total of 44 isolates were obtained which were belonged into 3 different phylum, as well as airborne bacteria, such as Actinobacteria, Firmicutes and Proteobacteria. The prevalent families were Bacillaceae, Burkholderiaceae, Nocardioidaceae, Microbacteriaceae and Micrococcaceae. There were 21 bacterial genera in mural samples. The frequently genera were Bacillus, Pseudomonas, Arthrobacter and Acimtobacter, followed by Aeromicrobium, Cupriavidus and Sphingomonas.According to the degree of color change on the test of the simulated cultivation, we screened 15 strains which could discolor the miniumite. Respectively, they were belonged to species Bacillus subtilis, Micrococcus luteus, Kocuria sp., Bacillus flexus, Planomicrobium sp., Naxibacter alkalitolerans, Pseudomonas sp. and Ramlibacter sp.. Including 6 airborne bacteria and 9 mural bacteria. And 12 strains which could discolor the iron oxide red. They were much similar to species Acinetobacter hvoffii, Arthrobacter sp., Cupriavidus gilardii, Acinetobacter schindleri, Pseudomonas stutzeri, Bacillus subterraneu, Bacillus sqfensis, Acinetobacter hvoffii. Including 7 airborne bacteria and 5 mural bacteria. The level of discoloration of miniumite pigment was higher than the iron oxide red, and effected more obvious in the low concentration than in the higher concentrations. In the simulation test of pigment color change, the chrome were changed into less red and yellow. This study could help to interpret the process of pigment color change by airborne and mural bacteria which were isolated from the culture heritage site.