BACTERIAL COMMUNITY OF COLORED COATINGS FROM YABELO ROCK ART SITE, ETHIOPIA. Geomicrobial Investigations of Colored Outer Coatings from an Ethiopian Rock Art Gallery

An open shelter in Yabelo, Ethiopia contains rock art paintings of great cultural importance. The paintings and rock substrate are covered by different mineral coatings, whose roles in rock art preservation are still unknown. Our objective is to investigate whether different colored rock coatings from the same rock art panel show diversity in chemical composition and microbiology. Two rock coatings are chosen for elemental analysis and bacterial characterization, one whitish (sample 1) and one reddish (sample 2). Although both samples are dominated by heterotrophic bacteria, the two coatings show distinct mineralogical and microbiological profiles. Sample 1 contains higher amounts of Ca and P than sample 2,which indicates the presence of organic matter. Sample 1 also shows bacterial genera potentially involved in biomineralization processes, metal redox cycles and metal resistance. On the other hand, sample 2 hosts mainly pathogenic and commensal bacteria from animal and human microbiota, and other microorganisms that are involved in nitrogen and metal biogeochemical cycles. Our results indicate that the bacterial communities are particular to the coating mineralogy, suggesting the possible involvement of microorganism in coatings formation. Unveiling the composition of the microbial communities in the coatings of prehistoric paintings has important implications to the conservation strategy.