Cave microorganisms and their role in the conservation and effective management of wild and show caves

Póster presentado en la S7. Biodeterioration: fundamentals, present and future perspectives. Session in honour of Prof. Cesáreo Sáiz Jiménez del 3rd International Congress Science and Technology for the Conservation of Cultural Heritage.-- Technoheritage 2017 21-24th May 2017, Cádiz, SpainMicrobial colonization of different substrata is one of the greatest threats for cultural heritage conservation. This problem constitutes a major challenge in subterranean environments (caves, catacombs, etc.), especially in those touristic sites. Walls, ceiling and sediments are usually coated with microbial communities in the form of colored spots (yellow, white, grey, rosy, etc.). For this reason in an hypogea conservation survey, identifying the microbial assemblages is one of the main aspect to be considered. Assessing their interactions with the diverse substrata (paintings, rocks, speleothems, etc.) is another main one. The microbial growth curves show that once installed on a substratum, the bacteria undergo a first lag phase or adaptation of their metabolism to the environmental conditions and substratum characteristics. This phase is characterized by a low rate of reproduction and growth of the microbial community, "they are but are not seen". The duration of this phase depends mainly on the nature and availability of nutrients. The main challenge is to find out the environmental and ecological conditions that make possible the persistence and development of a specie until the exponential growth phase is achieved. Knowing this, perhaps the future studies of conservation could be focused to avoid irreversible deterioration problems. Our previous researches show that microorganisms forming biofilms on rock surfaces interact with rock, water and underground air and have the ability to control their own micro-environment and to trigger large scale changes in cave environment. For this reason, it is necessary to develop environmental studies with the aim of characterizing each sub-environment in the studied underground ecosystem. In this study, we present some examples of biodeterioration by bacterial activity in different caves and underground archaeological sites. Different methods have been used: Electron microscopy observations revealed that a dense network of microorganisms composes these spots, which are coated with overlying bioinduced CaCO3 crystals. Molecular analysis indicated that these spots are mainly formed by complex assemblages of microorganisms, mainly undescribed species of the phylum Actinobacteria. On the other hand, CO2 efflux measurements in areas heavily colonized by bacteria indicated that some groups of bacteria have the ability to promote the uptake of this gas, usually very abundant in the caves. This leads to dissolution of the rock substratum and the precipitation of CaCO3 crystals during periods of lower humidity and/or CO2.Peer reviewe