Abstract
AbstractThe world cultural heritage sites face new challenges for an effective protection and management because of destruction and damage initiated by both natural and anthropogenic causes. Fresh rock and sandstone surfaces of buildings are quickly colonized and covered by a layer of microorganisms, including phototrophs, lithotrophs, and heterotrophs to form a biofilm that alters the local conditions of the stone surfaces, especially under the favorable tropical climate conditions for autotrophic microorganisms and plants. Biofilms had been studied with indigenous or pure cultures of isolated microorganisms, but the selective ones that contribute to deterioration of the cultural heritage cannot be confirmed easily. Currently, high-throughput sequencing and metegenomics analyses are capable of obtaining microbial community and composition in great depth, but they also suffer from similar weakness unable to identify the culprits in the community. With these as background, this article presents a different approach by focusing on the biochemical processes and the responsible microorganisms involved to reveal the destruction processes for management and protection. Among these different functional groups of microorganisms, lichens are known as pioneering rock-decomposing microorganisms, and both sulfur-oxidizing bacteria and fungi participate in the decomposition of sandstone via sulfur cycling and initiation of salt attack of the stone afterward, resulting in defoliation and cracking of stone. Other microorganisms including ammonia-oxidizing bacteria and archaea, especially the latter, have been recently detected on sandstone monuments providing evidence on the new organisms involved in the deterioration of cultural heritage and buildings. In addition, fungi can colonize the surfaces of the matured biofilms and play a new role in the removal of them, which has a potential biotechnological application in conservation of cultural heritage. The new proposed approach by focusing the microorganisms with identified biochemical function is more productive than a description of the community composition and assembly when assessing cultural heritage biodeterioration, and this provides basic and useful information for effective protection strategies and management.
Highlights
Deterioration of the world cultural heritage and historic buildings is a result of both natural and/or anthropogenic contributors involving flora, fauna, and microorganisms as well as pollutants
Coupling the relative high concentration of NO3À detected with the low pH condition and the more abundant AOA than AOB, an active biochemical process of ammonia oxidation or nitrification is operative on these cultural heritage to result in an accumulation of biogenic nitric acid, which contributes to the biodeterioration of sandstone
Stone cultural heritage and historic buildings are susceptible to colonization by microorganisms of a wide range of physiological characteristics depending on the environmental conditions and the stage of the development
Summary
Deterioration of the world cultural heritage and historic buildings is a result of both natural and/or anthropogenic contributors involving flora, fauna, and microorganisms as well as pollutants. Microbial community of Angkor monuments was analyzed initially with 16S rRNA gene-based polymerase chain reaction (PCR) and clone library (Lan et al 2010; Kusumi et al 2013) and, at the same time, isolation and identification of bacteria and fungi of the sulfur cycle and capable of acid production were focused at the beginning to obtain a general overview of the microbial assembly and their role on the potential destruction of these sandstone monuments under the tropical climate (Meng et al 2020; Mitchell and Gu 2000; Hosono et al 2006; Li et al 2010; Kusumi et al 2011; Hu et al 2013; Ding et al 2020). A new analysis reveals that Comammox bacteria, oxidizing ammonia directly to NO3À in a one-step reaction instead of the conventional two-step processes via nitrite as an intermediate, are detected on Preah Vihear Temple (Ding et al 2020)
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