Past, present and future methods of quantification in anatomical and ultrastructural studies of lichens

7 pages, figures, and tables statistics.This paper provides a general view of the state of the art in quantification methods for light and elctron microscopy, with especial reference to botany and lichenology.Peer reviewe

Contributions of in situ microscopy to the current understanding of stone biodeterioration

In situ microscopy consists of simultaneously applying several microscopy techniques without separating the biological component from its habitat. Over the past few years, this strategy has allowed characterization of the biofilms involved in biodeterioration processes affecting stone monuments and has revealed the biogeophysical and biogeochemical impact of the microbiota present. In addition, through in situ microscopy diagnosis, appropriate treatments can be designed to resolve the problems related to microbial colonization of stone monuments. [Int Microbiol 2005; 8(3):181-188

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

The weathering action of saxicolous lichens in maritime Antarctica

7 pages, figures and tables statistics.Xanthoria elegans (Link) Th Fr. and Lecidea lapicida (Ach.) were studied on volcanic andesite, and Rhizocarpon geooraphicum (L.) DC. and Bacidia stipata Lamb on a volcanigenic sediment, using light microscopy, infrared spectroscopy, X-ray diffraction and transmission electron microscopy. Feldspars were present in the rocklichen interface to a lesser extent than in the underlying rock. R. geographicum was found to alter the minerals in the rock on which it grew without producing any new minerals in the rock/lichen interface, in contrast to the observations for this species on granite in temperate regions. Beneath of the thallus of L. lapicida there was calcium oxalate and some micas of the illite type, which may have been degradation products of various phyllosilicates in the rock. B. stipata, an endemic Antarctic lichen, had the greatest capacity to weather the rock and had weddellite (dihydrate calcium oxalate) and calcite in the contact area as well as many bacteria. The presence of crystalline oxalate, imogolite, allophane, carbonates (calcite) and amorphous material not found in the parent rock indicates biomineralization processes attributable to the lichens.We are pleased to acknowledge that this work was supported by a grant number PB87 0229 from the Comisi6n Asesora de Ciencia y Tecnologia. We are grateful to Mr. F. Pinto and M. T. Carnota for technical assistance, and to Prof. Kappen and William Sanders for help with the English manuscript.Peer reviewe

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

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

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

Cretaceous mycelia preserving fungal polysaccharides: taphonomic and paleoecological potential of microorganisms preserved in fossil resins

The cortices of pieces of Cretaceous amber around the world commonly are constituted by networks of filamentous structures. Based on their morphological characteristics, such structures have previously been classified in different microorganismal groups. Their correct interpretation, however, is of great importance to establish the conditions of the resin's burial in the forest litter, and can provide important clues regarding the ecology and environmental conditions of Cretaceous resinous forests. Because these networks of filamentous structures present typical fungal morphological features we conducted a study in order to resolve their origin. The cortices of several pieces of Cretaceous amber from Spain were examined using light and scanning electron microscopy, energy dispersive X-ray spectroscopy, and confocal laser scanning microscopy. This is the first time that Calcofluor white and Wheat germ agglutinin conjugated with fluorescein isothiocyanate have been employed as fungal markers in amber, and their use enabled us to detect preserved polysaccharides in the filamentous structures using confocal laser scanning microscopy. These results provide the first and oldest record of ß-1,3 and ß-1,4-linked polysaccharides, and specifically N-acetylglucosamine residues from chitin in a fossil fungus preserved in amber, and to demonstrate that the networks of filamentous structures are mycelia composed of profuse hyphae of a resinicolous fungus. This type of mycelium constitutes one of the largest fungal fossil records known. Using taphonomic data, it is demonstrated that the cortices originated during the Cretaceous due to fungal growth within non-solidified resin. The fossil diagenetic degradation sequence of the fungal hyphae and the surrounding amber is described. This degradation changed the microscopic appearance of the hyphae; thus, some of the previously indicated taxonomic features of this microorganism may actually be fossil diagenetic artifacts. The paleoecological implications with regard to fungal trophic requirements and forest environmental conditions are discusse