Bacterial and Archaeal Structural Diversity in Several Biodeterioration Patterns on the Limestone Walls of the Old Cathedral of Coimbra.

Catarina Coelho,Nuno Mesquita,João Trovão,Inês Costa,Helena Freitas,Igor Tiago,Fabiana Soares,António Portugal

doi:10.3390/microorganisms9040709

Abstract

The “University of Coimbra-Alta and Sofia” area was awarded the UNESCO World Heritage Site distinction in 2013. The Old Cathedral of Coimbra, a 12th-century limestone monument located in this area, has been significantly impacted during the last 800 years by physical, chemical, and biological processes. This led to the significant deterioration of some of its structures and carvings, with loss of aesthetical, cultural, and historical values. For this work, deteriorated spots of the walls of three semi-open chapels from the cloister of the Cathedral were sampled to ascertain their bacterial and archaeal structural diversity. Based on Next-Generation Sequencing (NGS) result analysis, we report the presence of microbial populations that are well adapted to an ecosystem with harsh conditions and that can establish a diverse biofilm in most cases. While it was possible to determine dominant phylogenetic groups in Archaea and Bacteria domains, there was no clear connection between specific core microbiomes and the different deterioration patterns analyzed. The distribution of these archaeal and bacterial communities within the analyzed biodeterioration spots suggests they are more influenced by abiotic factors (i.e., water availability, salinity, etc.), although they influence (and are influenced by) the algal and fungal population composition in this ecosystem. This work provides valuable information that can assist in establishing future guidelines for the preservation and conservation of this kind of historic stone monuments.

Highlights

This study aimed at the determination of bacterial and archaeal community structural diversities and their distribution on dissimilar biodeterioration patterns, which were found on the limestone walls of three semi-open chapels from the cloister of the Old Cathedral of Coimbra
Thorough identification and characterization of the bacterial and archaeal populations in the limestone walls of the studied monument were attained in this study
We believe that salinity and water availability were the main abiotic factors influencing the microbial diversity detected, but that sunlight exposure and biotic interactions influenced the colonization by different groups

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Several endolithic and epilithic microbial communities have been reported in limestone monuments worldwide, which display diverse biodeterioration patterns depending on the different environmental conditions [1,2,3,4]. The most relevant factors affecting this colonization are physical (humidity, temperature, sunlight exposure, substrate porosity) and chemical (environmental pollution, substrate composition) [5,6,7]. The synergistic relationship with other colonizing organisms, as well as with the environmental conditions and urban pollution, can impact the microbial community composition, and influence their contribution to stone biodeterioration [5,6,7,8,9]

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