Microorganisms in desert rocks: the edge of life on Earth

This article reviews current knowledge on microbial communities inhabiting endolithic habitats in the arid and hyper-arid regions of our planet. In these extremely dry environments, the most common survival strategy is to colonize the interiors of rocks. This habitat provides thermal buffering, physical stability, and protection against incident UV radiation, excessive photosynthetically active radiation, and freeze-thaw events. Above all, through water retention in the rocks' network of pores and fi ssures, moisture is made available. Some authors have argued that dry environments pose the most extreme set of conditions faced by microorganisms. Microbial cells need to withstand the biochemical stresses created by the lack of water, along with temperature fl uctuations and/or high salinity. In this review, we also address the variety of ways in which microorganismsdeal with the lack of moisture in hyper-arid environments and point out the diversity of microorganisms that are able to cope with only the scarcest presence of water. Finally, we discuss the important clues to the history of life on Earth, and perhaps other places in our solar system, that have emerged from the study of extreme microbial ecosystems. [Int Microbiol (2012); 15(4):171-181

Study of lichens with different state of hydration by the combination of low temperature scanning electron and confocal laser scanning microscopies

The use of techniques such as low temperature scanning electron microscopy (LTSEM) and confocal laser scanning microscopy (CLSM) allows the study of lichen thalli in different states of hydration and also near the natural state. The spatial organization of desiccated thalli, with reduced, very compact algal layers, is different from that of hydrated ones. Sometimes, the observation with transmission electron microscopy (TEM) of photobiont pyrenoids from desiccated thalli reports pyrenoids with a central part of a weak stained matrix lacking pyrenoglobuli, named “empty zones”. “Empty zones” are not distinguishable with LTSEM and do not present immunolabelling with rubisco antibody in TEM. These zones could be originated by an expansion process during rehydration produced in chemical fixation

Microorganisms in desert rocks: the edge of life on Earth

This article reviews current knowledge on microbial communities inhabiting endolithic habitats in the arid and hyper-arid regions of our planet. In these extremely dry environments, the most common survival strategy is to colonize the interiors of rocks. This habitat provides thermal buffering, physical stability, and protection against incident UV radiation, excessive photosynthetically active radiation, and freeze-thaw events. Above all, through water retention in the rocks' network of pores and fi ssures, moisture is made available. Some authors have argued that dry environments pose the most extreme set of conditions faced by microorganisms. Microbial cells need to withstand the biochemical stresses created by the lack of water, along with temperature fl uctuations and/or high salinity. In this review, we also address the variety of ways in which microorganismsdeal with the lack of moisture in hyper-arid environments and point out the diversity of microorganisms that are able to cope with only the scarcest presence of water. Finally, we discuss the important clues to the history of life on Earth, and perhaps other places in our solar system, that have emerged from the study of extreme microbial ecosystems. [Int Microbiol (2012); 15(4):171-181

Ecology of endolithic lichens colonizing granite in continental Antarctica

In this study, the symbiont cells of several endolithic lichens colonizing granite in continental Antarctica and the relationships they have with the abiotic environment were analyzed in situ, in order to characterize the microecosystems integrating these lichens, from a microecological perspective. Mycobiont and photobiont cells, the majority classified as living by fluorescent vitality testing, were observed distributed through the fissures of the granite. The fact that extracellular polymeric substances were commonly observed close to these cells and the features of these compounds, suggest a certain protective role for these substances against the harsh environmental conditions. Different chemical, physical and biological relationships take place within the endolithic biofilms where the lichens are found, possibly affecting the survival and distribution of these organisms. The alteration of bedrock minerals and synthesis of biominerals in the proximity of these lichens give rise to different chemical microenvironments and suggest their participation in mineral nutrient cycling

Micromorphological characterization and lithification of microbial mats from the Ebro Delta (Spain)

The structural organization of microbial mats from the Ebro Delta (Spain) and their accretion and partial lithification processes were explored using scanning electron microscopy in back-scattered electron mode and low-temperature scanning electron microscopy. Two differentiated zones were distinguished in a transverse section of a fragment taken from the mat at a depth of 2.5 mm. The first consisted of an upper layer in which the dominant microorganisms, Microcoleus spp., actively grew in an embedded slack matrix of exopolysaccharides. Microcoleus filaments were oriented parallel to the surface and to each other, with filaments below arranged perpendicularly to one another but without crossing. Most of the minerals present were allochthonous grains of calcium phosphate biocorroded by cyanobacteria. The second zone was below a depth of 1 mm and made up of accretion layers with large deposits of calcium carbonate and smaller amounts of calcium phosphate of biological origin. The predominance of a particular type of mineral precipitation with a characteristic external shape and/or texture within a zone, e.g., sponge-like deposits of calcium phosphate, appears to depend on the taxa of the prevailing microorganisms. [Int Microbiol 2006; 9(4):289-295

Response of endolithic chroococcidiopsis strains from the polyextreme Atacama desert to light radiation

Cyanobacteria exposed to high solar radiation make use of a series of defense mechanisms, including avoidance, antioxidant systems, and the production of photoprotective compounds such as scytonemin. Two cyanobacterial strains of the genus Chroococcidiopsis from the Atacama Desert – which has one of the highest solar radiation levels on Earth- were examined to determine their capacity to protect themselves from direct photosynthetically active (PAR) and ultraviolet radiation (UVR): the UAM813 strain, originally isolated from a cryptoendolithic microhabitat within halite (NaCl), and UAM816 strain originally isolated from a chasmoendolithic microhabitat within calcite (CaCO3). The oxidative stress induced by exposure to PAR or UVR C PAR was determined to observe their short-term response, as were the long-term scytonemin production, changes in metabolic activity and ultrastructural damage induced. Both strains showed oxidative stress to both types of light radiation. The UAM813 strain showed a lower acclimation capacity than the UAM816 strain, showing an ever-increasing accumulation of reactive oxygen species (ROS) and a smaller accumulation of scytonemin. This would appear to reflect differences in the adaptation strategies followed to meet the demands of their different microhabitats.This study was supported by grant PGC2018-094076-B-I00 from MCIU/AEI (Spain) and FEDER (UE). MC was supported by grant BES 2014-069106 from the Spanish Ministry of Science and Innovation (MCINN).Peer reviewe

Double fossilization in eukaryotic microorganisms from Lower Cretaceous amber

<p>Abstract</p> <p>Background</p> <p>Microfossils are not only useful for elucidating biological macro- and microevolution but also the biogeochemical history of our planet. Pyritization is the most important and extensive mode of preservation of animals and especially of plants. Entrapping in amber, a fossilized resin, is considered an alternative mode of biological preservation. For the first time, the internal organization of 114-million-year-old microfossils entrapped in Lower Cretaceous amber is described and analyzed, using adapted scanning electron microscopy in backscattered electron mode in association with energy dispersive X-ray spectroscopy microanalysis. Double fossilization of several protists included in diverse taxonomical groups and some vegetal debris is described and analyzed.</p> <p>Results</p> <p>In protists without an exoskeleton or shell (ciliates, naked amoebae, flagellates), determinate structures, including the nuclei, surface envelopes (cortex or cytoplasmic membrane) and hyaloplasm are the main sites of pyritization. In protists with a biomineralized skeleton (diatoms), silicon was replaced by pyrite. Permineralization was the main mode of pyritization. Framboidal, subhedral and microcrystalline are the predominant pyrite textures detected in the cells. Abundant pyritized vegetal debris have also been found inside the amber nuggets and the surrounding sediments. This vegetal debris usually contained numerous pyrite framboids and very densely packed polycrystalline pyrite formations infilled with different elements of the secondary xylem.</p> <p>Conclusion</p> <p>Embedding in amber and pyritization are not always alternative modes of biological preservation during geological times, but double fossilization is possible under certain environmental conditions. Pyritization in protists shows a quite different pattern with regard to plants, due to the different composition and cellular architecture in these microorganisms and organisms. Anaerobic sulphate-reducing bacteria could play a crucial role in this microbial fossilization.</p

Discovery of carotenoid red-shift in endolithic cyanobacteria from the Atacama Desert

Las respuestas bioquímicas de las cianobacterias que habitan en las rocas hacia el estrés ambiental nativo se observaron in vivo en uno de los entornos climáticos extremos más desafiantes de la Tierra. La colonización criptoendolítica de cianobacterias, dominada por Chroococcidiopsis sp., Se estudió en una ignimbrita en un área volcánica de gran altitud en el desierto de Atacama, Chile. El cambio en la composición de carotenoides (desplazamiento al rojo) dentro de un transecto a través de la comunidad microbiana dominante de cianobacterias (grosor promedio de ~ 1 mm) se reveló inequívocamente en su microhábitat endolítico natural. La cantidad de carotenoides desplazados al rojo, observada por primera vez en un ecosistema microbiano natural, depende de la profundidad y se incrementa a medida que aumenta la proximidad a la superficie de la roca, como lo demuestra la resonancia Raman y la resonancia puntual del perfil Raman. Se atribuye a un cambio dependiente de la luz en la conjugación de carotenoides, asociado con la estrategia de adaptación a la luz de las cianobacterias. Se propone una hipótesis para el posible papel de un mecanismo de extinción no fotoquímica (NPQ) mediado por la proteína carotenoide naranja (OCP) que influye en el comportamiento espectral observado. Simultáneamente, se obtuvo información sobre la distribución de scytonemin y phycobiliproteins. Scytonemin fue detectado en los agregados de cianobacterias superiores. Se registró un gradiente de intensidad de señal inverso de las ficobiliproteínas, que aumenta con las posiciones más profundas como respuesta del complejo de captura de luz de cianobacterias a condiciones de poca luz.The biochemical responses of rock-inhabiting cyanobacteria towards native environmental stresses were observed in vivo in one of the Earth’s most challenging extreme climatic environments. The cryptoendolithic cyanobacterial colonization, dominated by Chroococcidiopsis sp., was studied in an ignimbrite at a high altitude volcanic area in the Atacama Desert, Chile. Change in the carotenoid composition (red-shift) within a transect through the cyanobacteria dominant microbial community (average thickness ~1 mm) was unambiguously revealed in their natural endolithic microhabitat. The amount of red shifted carotenoid, observed for the first time in a natural microbial ecosystem, is depth dependent, and increased with increasing proximity to the rock surface, as proven by resonance Raman imaging and point resonance Raman profiling. It is attributed to a light-dependent change in carotenoid conjugation, associated with the light-adaptation strategy of cyanobacteria. A hypothesis is proposed for the possible role of an orange carotenoid protein (OCP) mediated non-photochemical quenching (NPQ) mechanism that influences the observed spectral behavior. Simultaneously, information about the distribution of scytonemin and phycobiliproteins was obtained. Scytonemin was detected in the uppermost cyanobacteria aggregates. A reverse signal intensity gradient of phycobiliproteins was registered, increasing with deeper positions as a response of the cyanobacterial light harvesting complex to low-light conditions.• Ministry of Education, Youth and Sports (República Checa) y el National Sustainability Program I (NPU I). Beca LO1415 • CzeCOS ProCES. Proyecto CZ.02.1.01/0.0/0.0/16_013/0001609 • Ministerio de Economía y Competitividad. Proyecto CGL2013-42509P, para Jaket Wierzchos, Octavio Artieda, Carmen Ascaso, María Cristina CaseropeerReviewe