Factors Determining the Biodiversity of Halophilic Microorganisms on Historic Masonry Buildings

Abstract

The aim of the present study was to obtain insights into the relationship between the chemical (salt content and pH) and physico-mechanical (humidity and compressive strength) properties of mineral-based materials from historic buildings with salt efflorescence and the growth and biodiversity of halophilic microorganisms. Samples were mainly characterized by pH 6.5-8.5 and a moisture content of between 0.12 and 3.3%. Significant variations were also found in the salt content (sulfates, chlorides, and nitrates) of the materials. An SEM/EDS analysis of material surfaces revealed the presence of halite, calcite, gypsum, sodium sulfate, and potassium-sodium sulfate. Culture-dependent and culture-independent (clone library construction) approaches were both applied to detect halophilic microorganisms. Results derived from culturable methods and the materials analysis revealed a correlation between the total halophile count and pH value as well as sulfate content. A correlation was not observed between the concentration of chlorides or nitrates and the number of halophilic microorganisms. The materials studied were inhabited by the culturable halophilic bacteria Halobacillus sp., Virgibacillus sp., and Marinococcus sp. as well as the yeast Sterigmatomyces sp., which was isolated for the first time from mineral materials. Culture-independent techniques revealed the following bacterial species: Salinibacterium, Salinisphaera, Rubrobacter, Rubricoccus, Halomonas, Halorhodospira, Solirubrobacter, Salinicoccus, and Salinibacter. Biodiversity was the highest in materials with high or moderate salinity.

Black Fungi and Stone Heritage Conservation: Ecological and Metabolic Assays for Evaluating Colonization Potential and Responses to Traditional Biocides

“…Each crevice and intergrain space can become a salty micro-niche available for specialized microorganisms; along with the salt physical action, the selected community can contribute to stone structural destabilization [73][74][75][76]. The exclusive isolation of the halophilic fungi from sand disaggregated monuments only, highlighted as salt-attacked monuments constitute a suitable habitat for selected osmophilic/osmotolerant microorganisms [75,77,78]. However, this phenomenon seems to be progressive since Neoph.…”

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“…Curiously, members of the Rubrobacteria class were only detected in a relatively high proportion (23% of the phylum Actinobacteria) in S3, where it was possible to identify only the genus Rubrobacter. Unfortunately, it was not possible to infer at the species level, but species of this genus have been widely detected in terrestrial habitats, as stone monuments usually subjected to salt weathering (Otlewska et al 2017) as well as in marine environments, and some of them are known to be halotolerant, thermotolerant, and radiotolerant (Egas et al 2014).…”

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“…However, for the consistency of the bacterial amplicon analysis they were filtered out. Nevertheless, this result showed that halophilic microorganisms are abundant on the surfaces of masonry and mortar and should also be carefully studied as they can contribute to the deterioration of historic buildings [52].…”