Análisis, impacto y evolución de biofilms fotosintéticos en espeleotemas. El caso de la Cueva de Nerja

En cuevas y otros monumentos del patrimonio natural y cultural hipogeo, el desarrollo de organismos fotosintéticos en el entorno de las lámparas de luz eléctrica se conoce como mal verde (maladie verte) o flora de las lámparas (lampenflora o lamp flora). Con frecuencia, estos organismos forman parte de comunidades estructurales complejas, denominadas biofilms, que pueden inducir cambios físico-químicos en el sustrato colonizado. Cuando estas alteraciones son indeseables, tales como discoloración, disolución, ruptura o arenización se denominan biodeterioro. Conocer estas comunidades biológicas permite el diseño de estrategias para su control, en base a una adecuada conservación del patrimonio natural y cultural del medio subterráneo. En esta memoria se describen los trabajos de investigación realizados sobre los biofilms fotosintéticos que colonizan los espeleotemas de la Cueva de Nerja, con la finalidad de obtener información relativa a su biodiversidad, ecología y fisiología. Para ello se han empleado técnicas de fotomonitorización, análisis digital de imágenes, procesado estadístico y microscopía, estas últimas completadas con técnicas de análisis molecular. Los resultados obtenidos han permitido la descripción de biofilms con desarrollo epilítico y casmoendolítico, así como identificar aquellos factores ambientales que favorecen o perjudican su desarrollo. Estos biofilms inducen diferentes procesos de biodeterioro del sustrato y se forman por organismos fotosintéticos adaptados a las condiciones ambientales de la cavidad, en especial a la escasez de agua y una reducida iluminación. Chroococcidiopsis sp. y Cyanidium sp., considerados organismos extremófilos, han sido identificados como los grupos más abundantes y de presencia ubicua en la Cueva de Nerja. Otros géneros tales como Aphanothece, Leptolyngbya, Gloeocapsa, Pseudophormidium, Chalicogloea, Desmococcus, Jenufa, Stichococcus, Humidophila, Gloethece y Nostoc también han sido descritos. Entre las estrategias propuestas para controlar su desarrollo se encuentran evitar el aporte extraordinario de agua a la cavidad y el diseño de un sistema de iluminación eléctrica específico basado en la información pigmentaria ofrecida por las técnicas de microscopía. Por otro lado, los procesos de adaptación y las estrategias de resistencia que pueden desarrollar estos biofilms fundamentan la realización de ensayos, que incluyan la realización de estudios fisiológicos, previos a la realización de cambios definitivos en el sistema de iluminación de la cavidad

Cyanidium sp. Colonizadora de cuevas turísticas

4 páginas.-- 3 figuras..- 18 referencias.-- Comunicación presentada en el Congreso Estudio y Conservación del Patrimonio Cultural. Actas 16-19 de noviembre 2015, MálagaLas cuevas albergan variados grupos de microorganismos, entre los que se encuentran los de metabolismo fotosintético, que se desarrollan en las zonas iluminadas.1,2 En general, estos microorganismos forman parte de comunidades estructurales complejas denominadas biofilms, que también pueden estar formados por microorganismos heterótrofos e incluso pequeños invertebrados. De forma natural, los organismos fotosintéticos colonizan las zonas más externas de las cuevas pero en las cuevas turísticas, el sistema de iluminación eléctrica permite su desarrollo en las zonas más profundas, alrededor de los focos de luz. En estos medios es común la presencia de una flora que se relaciona con la otros ambientes aerofíticos, cuyo desarrollo depende de la biorreceptividad del sustrato y de las condiciones ambientales disponibles. La disponibilidad de algunos requisitos como agua, radiación fotosintética activa (PAR) o propiedades del sustrato determinan el tipo de microorganismo presente y su abundancia.N

Biological Control of Phototrophic Biofilms in a Show Cave: The Case of Nerja Cave

13 páginas.- 5 figuras.- 2 tablas.- 39 referenciasCyanobacteria and microalgae are usually found in speleothems, rocks and walls of show caves exposed to artificial lighting. These microorganisms develop as biofilms coating the mineral surfaces and producing aesthetic, physical and chemical deterioration. A wide number of physical, chemical and environmental-friendly methods have been used for controlling the biofilms with different results. Natural biological control has been suggested by some authors as a theoretical approach but without direct evidence or application. Here we report the finding of a natural biological control of phototrophic biofilms on the speleothems of Nerja Cave, Malaga, Spain. The formation of plaques or spots where the phototrophic microorganisms disappeared can be assumed on the basis of processes of predation of bacteria, amoebas and some other organisms on the phototrophic biofilms. This study aims at investigating the potentialities of the biological control of phototrophic biofilms in caves, but the originality of these data should be confirmed in future studies with a larger number of biofilm samples in different ecological scenarios.Peer reviewe

Vadose zone air as a biogenic source of methane in Nerja Cave system (South of Spain)

Subterranean air in karst cavities has often low methane contents in comparison to atmosphere and so karst systems have been considered a sink of atmospheric methane. Methane-oxidizing bacteria have been hypothesized as responsible for CH4 depletion in many caves around the world, although ionization radiation was also proposed as possible mechanism for this process. We measured CO2 and CH4 concentration and their C isotopic composition (d13C-CO2 and d13C-CH4) over 2 years within the Nerja cave system (South Spain) and in 9 boreholes drilled into the vadose zone (Triassic carbonate aquifer) surrounding the cave. According to d13C-CO2 and d13C-CH4 vadose zone of this karst system is a source of biogenic methane, produced both by acetate fermentation and CO2 reduction. Biogenic and atmospheric methane flows (along fractures from the vadose zone, and through ventilation, respectively) into the cave, where it is oxidized by methanotrophic bacteria that we detected on soil samples into the cave.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Condensation water in heritage touristic caves: Isotopic and hydrochemical data and a new approach for its quantification through image analysis

Condensation water is a major factor in the conservation of heritage caves. It can cause dissolution of the rock substrate (and the pigments of rock art drawn on it) or covering thereof with mineral components, depending on the chemical saturation degree of the condensation water. In show caves, visitors act as a source of CO2 and thus modify the microclimate, favouring negative processes that affect the conservation of the caves. In spite of their interest, studies of the chemical composition of this type of water are scarce and not very detailed. In this work we present research on the condensation water in the Nerja Cave, one of the main heritage and tourist caves in Europe. The joint analysis of isotopic, hydrochemical, mineralogical and microbiological data and the use of image analysis have allowed us to advance in the knowledge of this risk factor for the conservation of heritage caves, and to demonstrate the usefulness of image analysis to quantify the scope of the possible corrosion condensation process that the condensation water could be producing on the bedrock, speleothem and rock art. To our knowledge, this application of image analysis (relative to the condensation water in caves) is the first one of this type that has been documentedNerja Cave Foundation Funding for open access charge: Universidad de Málaga / CBU

Biofilms en cuevas turísticas: la Cueva de Nerja y la Cueva del Tesoro

11 páginas.-- 2 figuras.-- 41 referencias.-- Conferencia presentada en el Sexto Congreso Español sobre Cuevas Turísticas, celebrado en Nerja (Málaga), en septiembre/octubre de 2016.-- Descarga de las Actas en http://www.cuevasturisticas.es/cuevatur/docs/2016/pdf/LibroCuevastur2016.pdf[ES]: La geomorfología del medio subterráneo depende de su historia geológica, y de los fenómenos que lo modelan, como la erosión y otros agentes externos. Además, sobre los sedimentos, las paredes o los espeleotemas de cuevas se desarrollan poblaciones de microorganismos que modifican la superficie mineral. Así, la colonización de este medio estará en función de las condiciones ambientales, del grupo de microorganismos en cuestión y de la biorreceptividad de los sustratos. Las cuevas se consideran espacios especializados que se caracterizan por una temperatura uniforme, elevada humedad y escasos recursos nutricionales y energéticos. Las cuevas turísticas presentan mayor disponibilidad de energía, generada por la luz artificial y la entrada de materia orgánica, y favorecen la presencia de un mayor número de organismos fotosintéticos y heterótrofos. El desarrollo de microorganismos sobre las paredes y los espeleotemas de las cuevas pueden producir procesos de biodeterioro, es decir, cambios indeseables en el sustrato. En este trabajo se presenta la información obtenida sobre la microbiota que coloniza espeleotemas iluminados de dos cuevas turísticas, la Cueva de Nerja y la Cueva del Tesoro (Málaga), mediante el empleo combinado de la microscopía y del análisis molecular. Los resultados ponen de manifiesto que los microorganismos se organizan en comunidades estructurales complejas denominadas biofilms. El empleo de la microscopía ha permitido conocer la composición del sustrato y su relación con el biofilm, así como observar procesos de biodeterioro relacionados con cambios físicos y químicos del sustrato tales como decoloración, pérdida de consistencia, ruptura y disolución. En relación con la composición de los biofilms, se ha observado una biodiversidad dominada por cianobacterias y microalgas, junto con actinobacterias, proteobacterias, arqueas, hongos e incluso protozoos y pequeños artrópodos. El análisis molecular revela la presencia de nuevas especies de microorganismos en ambas cuevas. El conocimiento de estas comunidades, así como sus mecanismos de biodeterioro permite el diseño de medidas preventivas y correctoras destinadas al control y a una adecuada conservación del patrimonio natural y cultural de ambas cuevas.[EN]: The geomorphology of the subterranean environment depends on its geological history, and phenomena such as erosion and other external agents. Moreover, in the caves the development of microorganisms can change the surface of sediments, walls and speleothems. Therefore, the colonization of a cave will depend on the environmental conditions, the type of microorganisms involved and the substrata bioreceptivity. Caves are considered specialized areas characterized by a uniform temperature, high humidity and low nutritional and energy resources. Visited caves have more available energy, produced by artificial lighting and the input of organic matter, and these conditions allow the growth of photosynthetic and heterotrophic organisms. The development of microorganisms on the cave walls and speleothems may produce biodeterioration, i.e., undesirable changes in the substratum. This work provides information on the microbiota that colonizes illuminated speleothems in two tourist caves, Nerja and Tesoro (Málaga), through the combined use of optical and electron microscopy, together with molecular analysis. The results showed that, in both caves, microorganisms are organized into complex structural communities called biofilms. The microscopic approach provides data on the substratum composition and its relationship with the biofilm. Biodeterioration processes related to physical and chemical changes of the substratum such as discoloration, loss of consistency, breaking and dissolution, were also observed. The biofilms were dominated by cyanobacteria and microalgae together with actinobacteria, proteobacteria, archaea, protozoa, fungi and even small arthropods. Moreover, molecular analysis revealed the presence of new species of microorganisms in both caves. Knowledge about these communities and their mechanisms of biodeterioration allows the design of preventive and corrective actions, according with a proper conservation of natural and cultural heritage of both caves.N

Laser-induced breakdown spectroscopy of cyanobacteria in carbonate matrices under simulated Martian environment

The finding on the Martian surface of hydrated salt minerals, like carbonates and sulphates, and their interpretation as deriving from the desiccation of old bodies of water, has provided an evidence of liquid water activity on the surface of Mars [1]. These evaporite environments and their saline deposits are now a chief goal for planetary missions devoted to the search for fossil Martian life. Such minerals have the possibility of trapping and preserving over geologic times a biological record made up of halophilic extremophiles [1]. The existence of species of cyanobacteria that inhabit rock substrates on Earth, capable of growing in environments considered extreme, makes them ideal organisms for studying biological responses in different environmental conditions [2]. One possible organism detection strategy consists in the study of the most relevant emission lines and molecular bands attributed to presence of life by laser-induced breakdown spectroscopy (LIBS). However, the detection of these species can be complex as LIBS is sensitive to environmental conditions, such as the atmosphere composition and pressure, and could contribute to this signal [3]. In the present study, several species of cyanobacteria with dissimilar extremophilic characteristics [4] (tolerance to desiccation and salinity) were examined by LIBS. The identification and discrimination of cyanobacteria on carbonate substrates was based on organic signal emissions (C, C2, CN...) and the presence of other microelements (Fe, Si, Cu, K…). For this purpose, and to evaluate the influence of the surrounding atmosphere on the plasma composition and its contribution on LIBS signal, a set of samples including Arthrospira platensis (commercial), Microcystys aeruginosa (cultured) and Chroococcidiopsis sp. (natural samples) was analyzed under i) Mars-analogue atmosphere and ii) low air vacuum (7mbar)Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Selection of LED lighting systems for the reduction of the biodeterioration of speleothems induced by photosynthetic biofilms in the Nerja Cave (Malaga, Spain)

Electrical lighting favours the development of photosynthetic biofilms in caves which can induce biodeterioration in the colonized substrates. The use of specific lights as a limiting factor for biofilm growth could be effective in their control and represents an alternative to chemical methods since they can damage the substrate. However, studies about lighting and the photosynthetic activity of organisms in caves are scarce. In order to select the most effective LED light source in reducing photosynthesis and therefore, in reducing the growth rates of microalgae and cyanobacteria, four biofilms in the Nerja Cave were illuminated by several light emitted diodes (LEDs) with different spectral compositions and the photobiological responses were measured both by empirical and theoretical methodologies. The empirical approach was based on the photosynthetic efficiency, by measuring the in vivo chlorophyll a (Chl a) fluorescence and the theoretical approach was based on the photonic assimilation performance related to the proportion of the light quality used for photosynthesis, according to the action spectra for photosynthesis available in the literature. The photobiological responses showed differences between the empirical and theoretical approach mainly in biofilms dominated by cyanobacteria and red algae, probably because the available action spectra were not useful for monitoring these Nerja Cave biofilms. However, the expected spectral responses of photosynthesis were observed in green microalgal biofilms with maximum photosynthetic efficiency in red and blue light although the green light was also unexpectedly high. The high photosynthetic efficiency in green light could be explained by the predictable high chlorophyll content due to a very dark environment. The results were not conclusive enough for all the biofilm types to be able to recommend a specific lighting system for the photocontrol of biofilm expansion. (...)Funding for open access charge: Universidad de Málaga / CBUA. The project is financed by Cueva de Nerja Public Services Foundation and authorized by the Ministry of Culture of the Andalusian Government. This work is also a contribution to the Research Group FYBOA (RNM-295) of the Junta de Andalucía

Reverse pseudo-gours: a new sub-type of folia observed in the Nerja Cave (SE Spain)

A new sub-type of folia named “reverse pseudo-gour” has been observed and described in the Nerja Cave, southern Spain. It consists of fairly vertical, thin barriers (about 5 mm high and 2 mm thick) that develop on the underside of a sub-horizontal surface (shelfstone) and grow in the opposite direction to normal gours (rimstone dams), generating sinuous shapes. Their mineral composition is essentially calcium carbonate, although globular aggregates composed of clay and phosphate minerals have also been identified. The genesis and evolution of these reverse pseudo-gours occur just at the air-water interface and are controlled by (1) the sub-horizontality of the surface on which they develop, (2) scarce to very scarce calcite supersaturation, and (3) progressive and slow lowering of the water level. Thus, reverse pseudo-gours represent the shape limit to which a folia reaches when its development occurs just below a nearly horizontal ceiling and the feeding water saturation is extremely low. Although this new sub-type of folia has only been observed in the Nerja Cave, it is highly probable that it exists in several other caves around the world because the factors controlling its development are not very strict

Reverse pseudo-gours: a new sub-type of folia observed in the Nerja Cave (SE Spain)

A new sub-type of folia named “reverse pseudo-gour” has been observed and described in the Nerja Cave, southern Spain. It consists of fairly vertical, thin barriers (about 5 mm high and 2 mm thick) that develop on the underside of a sub-horizontal surface (shelfstone) and grow in the opposite direction to normal gours (rimstone dams), generating sinuous shapes. Their mineral composition is essentially calcium carbonate, although globular aggregates composed of clay and phosphate minerals have also been identified. The genesis and evolution of these reverse pseudo-gours occur just at the air-water interface and are controlled by (1) the sub-horizontality of the surface on which they develop, (2) scarce to very scarce calcite supersaturation, and (3) progressive and slow lowering of the water level. Thus, reverse pseudo-gours represent the shape limit to which a folia reaches when its development occurs just below a nearly horizontal ceiling and the feeding water saturation is extremely low. Although this new sub-type of folia has only been observed in the Nerja Cave, it is highly probable that it exists in several other caves around the world because the factors controlling its development are not very strict.This study has been financed by the Nerja Cave Foundation, coordinated by its Research Institute and authorized by the Consejería de Cultura (Junta de Andalucía). This study is also a contribution to the RNM-308 Research Group of the Junta de Andalucía and to the Projects PID2021-125619OB-C21, PID2021-125619OB-C22, TED2021-130549B-I00 funded by MCIN/AEI/10.13039/50110001103