Abstract
Local granite has been used throughout history in Galicia (NW Spain), forming the basis of much of the region’s architecture. Like any other rock, granite provides an ecological niche for a multitude of organisms that form biofilms that can affect the physical integrity of the stone. In this study, for the first time, characterization of the microbial consortium forming biofilms that developed on historical rural granite buildings is carried out using a combination of culture-dependent and next generation sequencing (NGS) techniques. Results pointed to differences in biofilm composition on the studied rural granite buildings and that of previously analyzed urban granite buildings, especially in terms of abundance of cyanobacteria and lichenized fungi. Exposure was corroborated as an important factor, controlling both the diversity and abundance of microorganisms on walls, with environmental factors associated with a northern orientation favoring a higher diversity of fungi and green algae, and environmental factors associated with the west orientation determining the abundance of lichenized fungi. The orientation also affected the distribution of green algae, with one of the two most abundant species, Trentepohlia cf. umbrina, colonizing north-facing walls, while the other, Desmococcus olivaceus, predominated on west-facing walls.
Highlights
Granite is one of the most commonly used types of stone in construction worldwide and is known to have been in use since Egyptian times [1]
Other abundant microorganisms in biofilms, such as bacteria and fungi were characterized by next generation sequencing (NGS) techniques, which allow a complete study of those species that are impossible to culture in the laboratory
[26], who studiedied thethe microbial diversity in granitic urban heritage, we found that apart, fungi andfungi greenand algae werealgae still the predominant, green were still the pregroups in thegroups biofilms
Summary
Granite is one of the most commonly used types of stone in construction worldwide and is known to have been in use since Egyptian times [1]. This igneous rock is widely used in construction because of its sustainability and durability, being a hard rock that is resistant to both heat and ultraviolet radiation. Interactions between the atmosphere and stone invariably lead to the formation of altered surface layers, which eventually results in damage to the original stone. This damage is of great concern in the case of stones in unique buildings and monuments [4]. Information about the biodeterioration of historical granite buildings is very limited relative to what is known about buildings constructed with limestone or sandstone [5], but it is known that the main factors leading to the granite biodeterioration process are the presence of soluble salts [6] and biodeterioration caused by colonizing organisms [7,8,9]
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