Abstract
Our cultural heritage kept in sandstone is doubtless suffering from accelerated biodeterioration. Fungi play a key role, either by acid production, dye secretion or as microbiont in the symbiotic association of the lichen with algae. The use of the universal initiators for the amplification of conserved regions of the ribosomal genes has been serving as an excellent marker for the microorganism identification, due to the ubiquity and conservation of these regions present in the genome of the eucarionts. In this chapter, the different fungi species present in sandstone were identified using molecular analysis techniques, as amplifiers in genes chains and the sequentiation of the resultant fragments. A theoric model of the way that the fungus contributes to the biodeterioration of monuments is proposed, with the objective of a better understanding of the contributions of these microorganisms in the general process of biodeterioration.
TopBackground
In Mexico, the phenomenon of biodeterioration not been studied systematically, but in the few cases has been focused primarily in the case of the Mayan archaeological zone of the Yucatan Peninsula, on composed mainly of limestone (Videla et al., 2000). In these, we have found a heterotrophic microflora composed of bacteria, fungi, and cyanobacteria colonizing structural materials of such sites. They have identified fungal genus such as Aspergillus and bacteria such as Pseudomonas and Bacillus.
The few studies that have been done on the role of microorganisms in processes of deterioration of stone have shown that the activity of microorganisms has helped the stone is solubilized, which weakens its crystal structure (Videla et al., 2000). That is why it is of great interest to study the biodeterioration presented in the siliceous rock, particularly as a material of which are made largely of colonial buildings in cities both in Mexico and internationally.
The first step in the study of biodeterioration and the establishment of the conditions that generate this phenomenon is the identification of participant microorganisms. The micro-flora found in the stones of the buildings represents a complex ecosystem that develops regarding both the environment in which the stones, as the physic-chemical properties of the materials. We can divide them into the following groups: Photolithoautotrophs. (Cyanobacteria, mosses and higher plants), Chemolithoautotrophs (Thiobacillus, Nitrosomonas, and Nitrobacter) and Chemoorganotrophs (fungi, bacteria, lichens symbiotic -associations fungi and algae or cyanobacteria) (Warscheid et al., 2000).
Biological growth plays an important role in the appearance of a monument, either as colorful lichens or ivy that give a romantic or old to a monument appearance, but also there is a variety of them that are related to the deterioration of stone or unsightly effects. Virtually all types of microorganisms (fungi, bacteria, cyanobacteria, algae, and lichens) can attack and damage the stone materials. Sometimes the mere presence of the organism is sufficient to promote the deterioration of the stone. However, in most cases, biodeterioration is associated with the metabolic activity of microorganisms, as well as the interaction of these substances with the essential components of the stone.
Key Terms in this Chapter
Initiator or Oligonucleotide: A short sequence of DNA (~ 17-22 bases) that binds to a target sequence in another DNA molecule and that helps to direct the synthesis of new DNA molecules using the consecutive polymerization of nucleotides at the end of each chain.
Electropherogram: Electrophoretic pattern obtained from DNA sequencing using an automatic sequencer. In these diagrams, each band of color corresponds to a different base (A, T, G, or C), because originally when sequencing the sample is marked with a different fluorophore each base.
Synergistic: It refers to two or more events that occur simultaneously and that participate in the common task of modulating an action. For example, biodeterioration is usually due to the joint action of environmental, chemical, biological factors, etc., which, acting together, are synergistic in the action of deteriorating the stone.
Litotrophe: Organism whose main environment is composed of diverse stone materials, whether those made of calcium, silicon, etc.
18S rRNA: Ribosomal RNA of the 18S sub-unit, is an RNA sequence that is transcribed from a gene within the nucleolar region of the cell. Once transcribed, the RNA binds proteins to be part of the small subunit of the ribosome called 18S.
Taq Polymerase: It is a thermostable enzyme with DNA polymerase activity that is responsible for the polymerization of DNA in a bacterial strain. Within the PCR this is used to simulate in vitro the polymerization action, and in this way synthesize and amplify DNA selectively.
Axenic: It refers to the cultivation of an organism that was originally in a mixed population, and that has gone through several replanting, in such a way that it can finally grow as a single colony, or also called “pure,” within a medium of culture.