The impact of stone position and location on the microbiome of a marble statue

Abstract

Microbial proliferation and biodeterioration constitutes a serious threat towards the preservation of stone monuments and relics. Geometry and exposure have been recently pinpointed as important factors determining the microbiome organization in stone monuments. In this work, the impacts of position and location on the microbial communities and their predicted metabolical and ecological profiles on a marble statue were studied. We sampled various epilithic stone biofilms from the Brotero statue (Coimbra’s UNESCO World Heritage site) and studied them by Next-generation Sequencing of the V3/V4 and the ITS2 regions, and bioinformatic analyses. We verified that statue location/heights have a more relevant impact than position/sides on the microbiome, and that Fungal and Chlorophyta communities showed a more diverse and less stable structural organization than Bacteria. Thus, while sub-aerial biofilms were mainly colonized by selective groups of extremophilic microorganisms, our results highlight that this specificity is more pronounced in prokaryotes. Bacterial metabolic functional distribution patterns were found to be distinct and adapted according to statue heights, while fungi displayed a strong domination of various types of saprotrophs. In addition to various “degraders” present in all samples, lower statue areas displayed strong connections with nitrogen fixators, while high and middle zones displayed stronger correlations with nitrogen and sulfur cycle bacteria. Moreover, biodeterioration at these sites can be promoted by biodeteriogenic cyanobacteria, bacteria linked to biogeochemical cycles, microcolonial Fungi and Chlorophyta able to thrive under hostile environments. In addition, mutualistic and competitive relationships between taxonomic groups were detected, that will require additional focus on future studies.