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Polar regions are likely the areas of the world where lichen communities show their highest degree of development leading to the formation of dense cryptogamic covers on soils. In these areas, lichens and bryophytes growing on the soil surface can be associated with different microorganisms, such as cyanobacteria and heterotrophic bacteria. Under that surface, edaphic prokaryotic (bacteria and archaea) and eukaryotic (algae and fungi) microorganisms coexist forming specific microbial communities. However, the diversity and roles of the microbiome in lichens from Polar Regions remains underexplored. Hence, we proposed to characterize the bacterial community structure of different lichens and mosses species colonizing glacier forefields from both Polar Regions, and the soils under them, in order to assess its specificity. To do so, we combined high-throughput amplicon sequencing with electron microscopy. Our results showed that bacterial communities differed less among microbiomes of cryptogamic covers dominated by different cryptogam species, than between these microbiomes and the bacterial communities from soils beneath. The edaphic bacterial community presented higher diversity than the cryptogamic cover microbiome, as shown by the higher abundance of specific edaphic OTUs. However, certain species specificity was also found in the microbiomes of different lichens and moss species. On the other hand, the microbial community structure of soils with cryptogamic cover was markedly different to that of the bare soils, suggesting a strong influence of the cryptogamic cover development on the edaphic communities. Finally, the electron microscopy revealed that bacteria appear mainly in non-healthy parts of the cryptogams, but also associated to the cell walls of some healthy cells and to soil particles integrated in the cover. All these results suggest that bacteria associated to cryptogamic covers might play an important role in their establishment and functioning, and c

Glacier forefields provide a unique chronosequence to assess microbial or plant colonization and ecological succession on previously uncolonized substrates. Patterns of microbial succession in soils of alpine and subpolar glacier forefields are well documented but those affecting high polar systems, including moraine rocks, remain largely unexplored. In this study, we examine succession patterns in pioneering bacterial, fungal and algal communities developing on moraine rocks and soil at the Hurd Glacier forefield (Livingston Island, Antarctica). Over time, changes were produced in the microbial community structure of rocks and soils (ice-free for different lengths of time), which differed between both substrates across the entire chronosequence, especially for bacteria and fungi. In addition, fungal and bacterial communities showed more compositional consistency in soils than rocks, suggesting community assembly in each niche could be controlled by processes operating at different temporal and spatial scales. Microscopy revealed a patchy distribution of epilithic and endolithic lithobionts, and increasing endolithic colonization and microbial community complexity along the chronosequence. We conclude that, within relatively short time intervals, primary succession processes at polar latitudes involve significant and distinct changes in edaphic and lithic microbial communities associated with soil development and cryptogamic colonization.

Himantormia lugubris is an Antarctic endemic with a distribution restricted to the northwest tip of Antarctic Peninsula, adjacent islands and South Georgia Island. In this region H. lugubris is an important component of the epilithic lichen community. The species has a fruticose thallus with usually simple and flattened branches whose grey surface is often disrupted exposing the black and dominant chondroid axis. Because the photobiont cells are mainly restricted to the patchy grey areas, positive carbon balance seems to be rather difficult for this species. Therefore, the aim of this paper is to elucidate which functional strategy, possibly linked with thallus anatomy, is used by H. lugubris that enables it to be a successful species in the maritime Antarctic. To achieve this goal, we constructed a picture of the lichen’s physiological, anatomical and morphological characteristics by using a broad range of technologies, such as chlorophyll fluorescence, CO exchange and electron microscopy. We found that H. lugubris has a very low net photosynthesis, apparently restricted to the grey areas, but high respiratory rates. Therefore, positive net photosynthesis is only possible at low temperatures. Chlorophyll content is also low but is present in both gray and black areas. Our conclusion is that the only possibility for this species to achieve a positive carbon balance is to be active for long periods under optimal conditions, that means, wet, cold and with enough light, a common combination in this region of Antarctica. Given these constrains, we suggest that H. lugubris is likely to be especially sensitive species to predicted climate warming in the maritime Antarctic.

We still lack studies that provide evidence for direct links between the development ofs oils urface cryptogamic communities and soil attributes and functioning. This is particularly truein areas free of potentially confounding factors suchas different soil types, landuses,oranthropogenic disturbances. Despite the ecológical importance of polar ecosystems and their sensitivity to climate change, we are far from understanding how their soils function and will respond to climate change-driven alteration sin above and below groundfeatures. We used two complementary approaches (i.e. cover gradients in the fore front of retreating glaciers as well as long-time deglaciated areas with well developed cryptogamic cover types) to evaluate the role of cryptogams driving multiples oil bioticanda bioticat tributes and function ingratesin polar terrestrial ecosystems. Increases in cryptogamic cover were consistently related to increases inorganic matter accumulation, soilfertility, and bacterial diversity, butal soin enhanced soil function ingrates in both sampling areas. However, we alsos how that theability to influence soil attributes varies among different polar cryptogamic covers, indicating that their differential ability to thrive under climate-change scenarios will largely determine the fate of polar soils in coming decades.

Mastodia es un género de hongos ascomicetos liquenizados perteneciente a la familia Verrucariaceae que establece simbiosis con algas verdes macroscópicas del género Prasiola (Trebouxiophyceae). En estudios anteriores, nuestro grupo de investigación examinó la filogeografía de ambos biontes a partir de poblaciones representativas del Hemisferio Norte (Alaska y Canadá) y Hemisferio Sur (Tierra del Fuego y península antártica), con importantes repercusiones para el conocimiento del origen de la funga liquénica antártica y de la distribución bipolar en líquenes. En el presente estudio se ahonda en la filogeografía de estos organismos en base a nuevos muestreos en Oceanía e islas del Océano Antártico. Algunas muestras provienen de islas remotas que fueron inspeccionadas con interés criptogámico por el botánico J.D. Hooker a mediados del siglo XIX, como por ejemplo las Kerguelen, Auckland, Campbell y Tasmania. Además, se investiga material de otras islas al norte y sur de Nueva Zelanda, las islas Marion y Macquarie, así como poblaciones que todavía no habían sido estudiadas genéticamente de la Tierra de Victoria (Antártida Continental). Algunas de las muestras de herbario analizadas exitosamente son históricas, datando de mediados de siglo pasado. Los primeros resultados plantean cuestiones interesantes sobre la diversidad y distribución geográfica de los linajes del hongo y alga liquenizados. De hecho, sin saberlo, Hooker recolectaría por primera vez un liquen cuyo estudio filogeográfico, más de un siglo y medio después, representaría una de las primeras investigaciones minuciosas de biogeografía de líquenes en el Hemisferio Sur y, en particular, en el ámbito insular.

Lichens are present in most terrestrial ecosystems on Earth and colonize extreme habitats, where vascular plants are unable to thrive, due to unique properties of the fungal-algal symbiosis. Here, we explored the phylogeographic structure of green algae engaged in symbiosis with species in the genus Pseudephebe (Parmeliaceae). These often form deep brown to blackish fruticose thalli on acidic rocks, and have partially overlapping distributions: P. minuscula is bipolar and co-occurs with P. pubescens in Europe. Based on a broad sampling, including the Arctic and Antarctica, we focused on photobionts (1) to identify genetic lineages and their phylogenetic assignment, (2) to infer the haplotype distribution in relation with geography and the mycobiont¿s identity, and (3) to evaluate spatial genetic structure and polymorphism. Results revealed three Trebouxia clade S lineages (Trebouxia S02, T. suecica and T. angustilobata) associated to Pseudephebe species, with predominant haplotypes distributed throughout the entire geographic distribution, and some, less frequent, shared between widely distant localities. Photobiont switching was evident in the Mediterranean region, and algal co-occurrence was frequent in both mycobionts, which shared the same set of photobionts; this could explain, at least partially, their overlapping distribution. Furthermore, genetic structure was influenced by geography given the substantial percentages of genetic variation (ca. 25¿50%) explained by the different delimited eco¿/biogeographic regions. In Continental Antarctica, mycobionts showed a high specialization towards the photobionts, which are probably endemic of this climatically extreme region. Taken together, our findings provide further insight about the processes shaping lichen biogeography.

Microorganisms can survive in extreme environments and oligotrophic habitats thanks to their specific adaptive capacity. Due to its severe and contrasting climate conditions, the cold mountain desert in Eastern Pamir provides a unique environment for analyzing microbial adaptation mechanisms occurring within colonization of endolithic habitats. This study aims to investigate the composition and structure of endolithic microbial communities and analyze the interactions between microorganisms and colonized lithic substrates. Endolithic biofilms were examined using scanning electron microscopy in backscattered electron mode (SEM-BSE) and next-generation sequencing (NGS) applying amplicon sequence variants (ASVs) approach. The investigation of the V3–V4 region of 16S rRNA gene revealed that endolithic communities are dominated by Actinobacteria (26%), Proteobacteria (23%), and Cyanobacteria (11.4%). Cyanobacteria were represented by Oxyphotobacteria with a predominance of subclasses of Oscillatoriophycidae, Synechococcophycideae, and Nostocophycidae as well as the rarely occurring Sericytochromatia. The positive correlation between the contribution of the orders Synechococcales and Rhizobiales to community structure suggests that some functionally closed taxa of Cyanobacteria and Proteobacteria can complement each other, for example, in nitrogen fixation in endolithic communities. The endolithic communities occurring in Eastern Pamir were identified as complex systems whose composition and structure seem to be influenced by the architecture of microhabitats and related microenvironmental conditions.

Investigadores del CSIC nos cuentan cómo es trabajar en el Continente helado

The assembly of single-amplified genomes (SAGs) and metagenome-assembled genomes (MAGs) has led to a surge in genome-based discoveries of members affiliated with Archaea and Bacteria, bringing with it a need to develop guidelines for nomenclature of uncultivated microorganisms. The International Code of Nomenclature of Prokaryotes (ICNP) only recognizes cultures as ‘type material’, thereby preventing the naming of uncultivated organisms. In this Consensus Statement, we propose two potential paths to solve this nomenclatural conundrum. One option is the adoption of previously proposed modifications to the ICNP to recognize DNA sequences as acceptable type material; the other option creates a nomenclatural code for uncultivated Archaea and Bacteria that could eventually be merged with the ICNP in the future. Regardless of the path taken, we believe that action is needed now within the scientific community to develop consistent rules for nomenclature of uncultivated taxa in order to provide clarity and stability, and to effectively communicate microbial diversity

Lichens represent a symbiotic relationship between at least one fungal and one photosynthetic partner. The association between the lichen-forming fungus Mastodia tessellata (Verrucariaceae) and different species of Prasiola (Trebouxiophyceae) has an amphipolar distribution and represents a unique case study for the understanding of lichen symbiosis because of the macroalgal nature of the photobiont, the flexibility of the symbiotic interaction and the co-existence of free-living and lichenized forms in the same microenvironment. In this context, we aimed to (1) characterize the photosynthetic performance of co-occurring populations of free-living and lichenized Prasiola and (2) assess the effect of the symbiosis on water relations in Prasiola, including its tolerance of desiccation and its survival and performance under sub-zero temperatures.

An interesting biota of lichen-forming fungi occurs along rocky seashores of cold and warm-temperate regions in both hemispheres. Most of the species belong to the family Verrucariaceae and form symbioses with an extraordinarily diverse group of photobionts. We isolated the photobionts of three species: Hydropunctaria maura and H. amphibia from the supralittoral zone, and ahlenbergiella striatula from the upper intertidal zone. We characterized the isolated strains structurally by means of transmission electron microscopy, and molecularly using the nrSSU and nrITS and chloroplast RPL10A regions. Additionally, we studied the response of the strains to different salt concentrations, analyzed the concentration of osmoregulatory solutes, and measured photosynthesis performance by chlorophyll fluorescence and CO2 assimilation techniques. All strains belong to the recently described species Halofilum ramosum, although we found differences in the ITS and RPL10A regions among the strains shared by H. maura and H. amphibia and the strain isolated from W. striatula. Differences were also found in the main osmoregulatory response of the strains growing under high salt concentrations: W. striatula accumulated glycerol, while H. maura and H. amphibia synthetized sucrose. Analyses of photosynthesis performance also indicated differences in physiological behavior between supralittoral-dwelling and intertidal-dwelling species, W. striatula showing lower photosynthetic activity under high irradiance. Our results highlight the role of hotobionts in determining lichen zonation on rocky seashores.

A recent field study indicated that thalli of the beard lichen Ramalina usnea undergo diffuse (intercalary) growth throughout their length. We examined thallus sections with TEM to better understand how the highly thickened cell walls of the prosoplectenchymatous cortex behave under conditions of continued expansion. Cell protoplasts were surrounded by massive accumulations of structured electron-dense wall layers interspersed with amorphous, electron-transparent substances, visible as concentric rings in transverse section. Nearest the protoplast, electron-dense wall layers were distinct and more or less alternated with irregular deposits of electron-transparent material. With increasing distance from the protoplast, the electron-dense wall layers were increasingly disrupted and intermixed among the electron-transparent materials. New cell branches grew through the accumulated wall materials, interrupting the layers they penetrated while producing their own concentric wall layers. The differing amounts of cell wall material accumulated was further indication of the different relative ages of such neighbouring cells. These observations suggest that cell walls are disrupted by diffuse tissue expansion and continually replaced by new walls and wall materials deposited to their interior at the interface with the protoplast. This pattern of development, documented previously in R. menziesii and U. longissima, suggests that component cells of lichen prosoplectenchyma behave quite differently from those of diffusely expanding filaments studied in non-lichen-forming fungi, where a single, discrete cell wall is maintained throughout growth.

[EN] The formation of secondary copper deposits, the source of more than half of the world's production, is usually interpreted as abiogenic. In this study of the Las Cruces deposit (southwestern Spain), in situ hybridization and scanning electron microscopy analysis together with integrated genomic and bioinformatic studies on cultures provide compelling evidence that a microbial community controls the current formation of the secondary copper mineralization. The cementation zone of this deposit contains abundant microbial life dominated by sulfate-reducing bacteria that coexist with methanogens and with other prokaryotes having unknown roles. Fractures in the primary massive sulfides are coated by extracellular polymeric substances in which the microbial cells are embedded. Covellite crystals have nucleated within these microbial aggregates, accreting and forming large crystals attached to the vein walls. These results strongly suggest that in situ microbial sulfate reduction can control the formation of secondary copper deposits. Equivalent processes could be widespread in similar deposits elsewhere, but they are probably overlooked due to the presumed low capability for fossilization of the microbes.

According to a widely held view, fungi do not produce parenchymatous tissues. Following up on recent transmission electron microscopy (TEM) evidence that challenged this paradigm in several lichens, we employed scanning electron microscopy (SEM) to investigate the orientation of new anticlinal walls in the single-layered fungal cortex of six species of Collemataceae, a family of gelatinous cyanolichens with diverse surface morphologies. Examination of thallus surfaces in four species of Leptogium (L. austromericanum, L. burnetiae, L. chloromelum, L. marginellum) and two species of Scytinium (S. gelatinosum, S. lichenoides) revealed that recently formed septa adjoin to preceding septa in parenchymatous division. These cortical divisions were evident in the formation and development of thallus wrinkles, folds, isidia, and lobules in the six morphologically distinct taxa. Tomentum, by contrast, arose as filamentous outgrowths of the cortical cells. We conclude that the monostromatic cellular cortex in Collemataceae participates in surface growth and morphogenesis by means of parenchymatous cell divisions, in a remarkable parallel to plant meristems. Cortical cell divisions do not appear to drive morphogenesis, however, as very similar morphologies are achieved in the closely related genus Collema, which lacks a cortex altogether. These results provide evidence that parenchymatous cell division can indeed play a role in morphogenesis of fungal structures and show that SEM is a useful tool for distinguishing the orientation of anticlinal divisions in the cortex of gelatinous lichens.

Some definitions of the term ‘lichen’ have often emphasized the role of the mycobiont as exhabitant in the symbiosis. Mastodia tessellata and Turgidosculum ulvae, both forming lichen-like associations with foliose algae, have traditionally defied that definition. In this study, we delve into the poorly known association of T. ulvae with Blidingia minima. Using four molecular markers (nrLSU, nrSSU, RPB1, mtSSU) we show that T. ulvae is a member of the family Verrucariaceae, closely related to the marine species Verrucaria ditmarsica. The presence of bitunicate asci and single-cell ascospores is confirmed. Our analysis of a fragment of the rbcL marker demonstrates that the photosynthetic partner belongs to B. minima, although relationships within this taxon remain unclear. Transmission electron microscopy allowed us to illustrate how T. ulvae interacts with Blidingia cells, and how haustoria in that species differ from those previously investigated in other marine lichen-forming fungi.

How growth is distributed within the morphologically diverse thalli of lichens is still poorly known and the anatomical mechanisms involved are not well understood. This work applies electron microscopy (SEM and TEM) to examine cell- and tissue-level events in the umbilicate thallus of Lasallia pustulata, whose pattern of expansion was the subject of a previous field study. Stacks of epinecral tissue accumulating at the thallus surface showed broadening bases and recurring rupture attributable to diffuse expansion of the living tissue below. Cortical cells, dividing anticlinally, adjoined septa to previous septa, indicating parenchymatous divisions. These observations are all consistent with previous contentions that mature, organized tissues within the thallus are capable of continued diffuse growth. They provide a developmental explanation for the morphology of the epinecral layer and suggest that anatomical characteristics may be helpful in recognizing diffuse growth patterns. Parenchymatous cell divisions, believed until recently to never occur in lichen thallus tissues, are shown to play a developmental role in the diffuse growth of the umbilicate lichen thallus.

Aim The hypotheses proposed to explain the high percentage of bipolar lichens in Antarctica have never been explicitly tested. We used the strictly bipolar, coastal lichenized fungus Mastodia tessellata (Verrucariaceae, Ascomycota) and its photobionts (Prasiola, Trebouxiophyceae, Chlorophyta) as model species to discern whether this extraordinary disjunction originated from vicariance or long-distance dispersal. Location Coasts of Antarctica, Tierra del Fuego (Chile), Alaska (USA) and British Columbia (Canada). Methods Based on a comprehensive geographical (315 specimens and 16 populations from Antarctica, Tierra del Fuego and North America) and molecular sampling (three and four loci for the fungus and algae respectively), we implemented explicit Bayesian methods to compare alternative hypotheses of speciation and migration, and performed dating analyses for the fungal and algal partner, in order to infer the timing of the colonization events and the direction of gene flow among distant, disjunct areas. Results Mastodia tessellata comprises two fungal species which in turn associate with three photobiont lineages along the studied distribution range. Independent estimation of divergence ages for myco- and photobionts indicated a middle to latest Miocene species split in the Southern Hemisphere, and a late Miocene to Pleistocene acquisition of the bipolar distribution. Comparison of migration models and genetic diversity patterns suggested an austral origin for the bipolar species. Main conclusions The complex evolutionary history of Mastodia tessellata s.l. can be explained by a combination of vicariant and long-distance dispersal mechanisms. We provide novel evidence of a pre-Pleistocene long-term evolution of lichens in Antarctica as well as for bipolar distributions shaped by Southern to Northern Hemisphere migratory routes without the need for stepping stones.

Ecologists have long studied primary succession, the changes that occur in biological communities after initial colonization of an environment. Most of this work has focused on succession in plant communities, laying the conceptual foundation for much of what we currently know about community assembly patterns over time. Because of their prevalence and importance in ecosystems, an increasing number of studies have focused on microbial community dynamics during succession. Here, we conducted a meta-analysis of bacterial primary succession patterns across a range of distinct habitats, including the infant gut, plant surfaces, soil chronosequences, and aquatic environments, to determine whether consistent changes in bacterial diversity, community composition, and functional traits are evident over the course of succession. Although these distinct habitats harbor unique bacterial communities, we were able to identify patterns in community assembly that were shared across habitat types. We found an increase in taxonomic and functional diversity with time while the taxonomic composition and functional profiles of communities became less variable (lower beta diversity) in late successional stages. In addition, we found consistent decreases in the rRNA operon copy number and in the high-efficient phosphate assimilation process (Pst system) suggesting that reductions in resource availability during succession select for taxa adapted to low-resource conditions. Together, these results highlight that, like many plant communities, microbial communities also exhibit predictable patterns during primary succession.

Following the retreat of a glacier, microbial colonization paves the way for future plant successions as nutrients are gradually introduced into the ecosystem. Characterizing the dynamics of this initial microbial colonization process is a key to understanding how these rapidly receding glacier areas are colonized. This study examines primary successions of bacteria, fungi and algae in two glacier forefields chronosequences on opposite slopes of Cordillera Darwin (Tierra del Fuego, Chile). Both slopes (southern and northern) show contrasting climate factors along with rapid rates of plant succession. Through a high-throughput sequencing approach, we identified Cyanobacteria as the dominant bacteria in younger soils close to the glacier terminus, whereas abundances of Alphaproteobacteria and Acidobacteria increased with soil surface age. Lichen-forming fungi and parasitic fungi were the most abundant fungal groups in younger succession stages, while saprophytic and mycorrhizal orders dominated later stages. The order Prasiolales predominated algal communities close to the glacier terminus, while Microthamniales and Chlamydomonadales orders dominated subsequent succession stages. Our observations reflect a changing community structure over time of the three microbial groups examined, and the replacement of taxa during the succession. Changes in composition are especially marked between the youngest succession states and subsequent ones in both forefields. Simultaneous analysis of bacterial, fungal and algal communities revealed the different trajectories of the three groups, with bacterial and fungal communities showing more marked succession patterns. Our results point to more relevant roles for bacteria at the initial stages of succession, while fungi could play a dominant role over bacteria as succession progresses. The ubiquity of algal taxa along the chronosequences was also observed. The two glacier forefields showed different microbial temporal dynamics, indica

The hyper-arid central region of the Namib Desert is characterized by quartz desert pavement terrain that is devoid of vascular plant covers. In this extreme habitat the only discernible surface covers are epilithic lichens that colonize exposed surfaces of quartz rocks. These lichens are highly susceptible to disturbance and so field surveys have been limited due to concerns about disturbing this unusual desert feature. Here we present findings that illustrate how non-destructive surveys based upon advanced photogrammetry techniques can yield meaningful and novel scientific data on these lichens. We combined 'structure from motion analysis,' computer vision and GIS to create 3-dimensional point clouds from two-dimensional imagery. The data were robust in its application to estimating absolute lichen cover. An orange Stellarangia spp. assemblage had coverage of 22.8% of available substrate, whilst for a black Xanthoparmelia spp. assemblage coverage was markedly lower at 0.6% of available substrate. Hyperspectral signatures for both lichens were distinct in the near-infra red range indicating that Xanthoparmelia spp. was likely under relatively more moisture stress than Stellarangia spp. at the time of sampling, and we postulate that albedo effects may have contributed to this in the black lichen. Further transformation of the data revealed a colonization preference for west-facing quartz surfaces and this coincides with prevailing winds for marine fog that is the major source of moisture in this system. Furthermore, a three-dimensional 'fly through' of the lichen habitat was created to illustrate how the application of computer vision in microbiology has further potential as a research and education tool. We discuss how advanced photogrammetry could be applied in astrobiology using autonomous rovers to add quantitative ecological data for visible surface colonization on the surface of Mars.

Cryptic microbial communities develop within rocky substrates in Antarctica’s McMurdo Dry Valleys as a stress avoidance strategy. They may be cryptoendolithic within pore spaces of weathered rocks, or develop in cracks and fissures as chasmoendolithic communities and are characterised by coloured bands of colonisation. Here we used a precision drill to recover fractions from black, white, green and red layers within colonised granite and sandstone. We combined backscattered scanning electron microscopy and high-throughput sequencing to identify major taxa in each band. We confirmed the presence of algal and fungal lichen symbionts, cyanobacteria and free-living algae, plus a diverse heterotrophic bacterial and archaeal component. A clear delineation at the community level was observed. The relatively biodiverse and heterogenous lichen communities occurred in weathered sandstone cliffs, whilst in granite and sandstone boulders, cyanobacterial communities were dominant. Differences between coloured bands of colonisation within each community were less clear. The study demonstrates that endolithic microbial communities can be recovered using a drill technology similar to that planned for the search for endolithic biosignatures on Mars.

Global patterns in diversity were estimated for cyanobacteria-dominated hypolithic communities that colonize ventral surfaces of quartz stones and are common in desert environments. A total of 64 hypolithic communities were recovered from deserts on every continent plus a tropical moisture sufficient location. Community diversity was estimated using a combined t-RFLP fingerprinting and high throughput sequencing approach. The t-RFLP analysis revealed desert communities were different from the single non-desert location. A striking pattern also emerged where Antarctic desert communities were clearly distinct from all other deserts. Some overlap in community similarity occurred for hot, cold and tundra deserts. A further observation was that the producer-consumer ratio displayed a significant negative correlation with growing season, such that shorter growing seasons supported communities with greater abundance of producers, and this pattern was independent of macroclimate. High-throughput sequencing of 16S rRNA and nifH genes from four representative samples validated the t-RFLP study and revealed patterns of taxonomic and putative diazotrophic diversity for desert communities from the Taklimakan Desert, Tibetan Plateau, Canadian Arctic and Antarctic. All communities were dominated by cyanobacteria and among these 21 taxa were potentially endemic to any given desert location. Some others occurred in all but the most extreme hot and polar deserts suggesting they were relatively less well adapted to environmental stress. The t-RFLP and sequencing data revealed the two most abundant cyanobacterial taxa were Phormidium in Antarctic and Tibetan deserts and Chroococcidiopsis in hot and cold deserts. The Arctic tundra displayed a more heterogenous cyanobacterial assemblage and this was attributed to the maritime-influenced sampling location. The most abundant heterotrophic taxa were ubiquitous among samples and belonged to the Acidobacteria, Actinobacteria, Bacteroidetes, a

Symbiotic associations between green algae (Chlorophyta) and fungi give rise to morphologically and eco-physiologically distinct entities, or so-called, lichens. In one of the most peculiar of these associations, the partners are species of the macroscopic genus Prasiola (Trebouxiophyceae) and the ascomycete Mastodia tessellata (Verrucariaceae). This is the only known case of a lichen symbiosis involving a foliose green alga. Despite intense research targeted at understanding the biology of this particular association, little is known about the genetic variability of its symbionts. This study focuses on the photobiont partner of this lichen and was designed to explore and compare its genetic diversity along a latitudinal axis from Alaska to Antarctica. Molecular sequence data were generated for three loci: two nuclear markers (nrITS, RPL10A) and one plastid-encoded marker (tufA). The usefulness of the Prasiola nrITS and RPL10A data was examined at the species and intraspecific levels. We used the population assignment tests implemented in BAPS and STRUCTURE and two algorithmic species delimitation procedures (ABGD, GMYC) to generate species boundary discovery hypotheses, which were subsequently tested using Bayes factors. Population genetic differentiation and structure were also assessed through fixation indices, polymorphism statistics and haplotype networks. Based on the results of the species validation method, we propose that at least two species of Prasiola associate with the lichen-forming fungus Mastodia tessellata. Of these, P. borealis is broadly distributed in Alaska, Tierra del Fuego and the Antarctic Peninsula, whereas the second, undescribed, species is restricted to the Antarctic Peninsula. We detected significant phylogeographic substructure in P. borealis, including greater haplotype diversity in the Tierra del Fuego populations. Our findings provide new data that will be useful to unravel the cryptic diversity and phylogeographic patterns of the gr

Knowledge on lichen and microbial colonization as well as associated biodeterioration processes of the stone cultural heritage is needed to establish proper conservation programs, but is still poor for stonework in semi-arid regions. In this study, lichen diversity was characterized on seven monumental buildings of the Pasargadae UNESCO-world heritage site (Iran). The risk of biodeterioration processes associated to lichen occurrence on two types of limestones, and the lichen resilience to mechanical cleaning intervention were examined. Physico-chemical substrate features and climatic conditions, combined with the agricultural surrounding and tourist disturbance, supported a pervasive colonization by species-poor epi- and endolithic communities, and fast recolonization processes by nitrophytic species after mechanical removal. The endolithic growth of some lichens and the penetration of hyphal structures of epilithic ones, examined by light and electron microscopy, were associated to stone disintegration and dissolution at the lichen-rock interface. Endolithic cyanobacteria were detected under lichen thalli, likely contributing to deterioration processes. Colonization and deterioration patterns did not appear peculiar with respect to previous investigations on similar communities in different climatic regions, and were mostly related to the different examined lithologies, indicating lichens as harmful biodeteriogens of the sedimentary rock materials used in the stone cultural heritage of semi-arid regions.

PREMISE OF THE STUDY: Lichen-forming fungi produce diverse vegetative tissues, some closely resembling those of plants. Yet it has been repeatedly affirmed that none is a true parenchyma, in which cellular compartments are subdivided from all adjacent neighbors by cross walls adjoining older cross walls. METHODS: Using transmission electron microscopy (TEM), we tested this assumption by examining patterns of septum formation in the parenchyma-like cortex of three lichens of different phylogenetic affinities: Sticta canariensis, Leptogium cyanescens, and Endocarpon pusillum. KEY RESULTS: In the cortex of all three lichens, new septa adjoined perpendicularly or obliquely to previous septa. Septal walls possessed an electron-transparent core (median) layer covered on both sides by layers of intermediate electron density. At septal junctures, the core layer of the newer septum was not continuous with that of the older septum. Amorphous, electron-dense material often became deposited in the core region of older septal walls, and the septum gradually delaminated along its median into what could then be recognized as the distinct walls of neighboring cells. However, cells maintained continuity at pores, where adjacent remnants of the electron-transparent core layer suggested septal partition rather than secondary establishment of a lateral wall connection via anastomosis. CONCLUSIONS: Although fungal tissues first arise by the coalescence of filaments early in lichen ontogeny, the mature cortical tissues of some lichens are comparable to true parenchyma in the unrestricted orientation of their septal cross walls and the resulting ontogenetic relationship among neighboring cell compartments.

Laser irradiation of lichen thalli on heritage stones serves for the control of epilithic and endolithic biolog- ical colonizations. In this work we investigate rock samples from two quarries traditionally used as source of monumental stone, sandstone from Valonsadero (Soria, Spain) and granite from Alpedrete (Madrid, Spain), in order to find conditions for efficient laser removal of lichen thalli that ensure preservation of the lithic substrate. The samples presented superficial areas colonized by different types of crustose lichens, i.e. Candelariella vitellina, Aspicilia viridescens, Rhizocarpon disporum and Protoparmeliopsis muralis in Valonsadero samples and P. cf. bolcana and A. cf. contorta in Alpedrete samples. A comparative laser cleaning study was carried out on the mentioned samples with ns Q-switched Nd:YAG laser pulses of 1064 nm (fundamental radiation), 355 nm (3rd harmonic) and 266 nm (4th harmonic) and sequences of IR-UV pulses. A number of techniques such as UV-Vis absorption spectroscopy, stereomicroscopy, scan- ning electron microscopy (SEM) at low vacuum, SEM with backscattered electron imaging (SEM-BSE), electron dispersive spectroscopy (EDS) and FT-Raman spectroscopy were employed to determine the best laser irradiation conditions and to detect possible structural, morphological and chemical changes on the irradiated surfaces. The results show that the laser treatment does not lead to the complete removal of the studied lichen thalli, although clearly induces substantial damage, in the form of loss of the lichen upper cortex and damage to the algal layer. In the medium term these alterations could result in the destruction of the lichen thalli, thus providing a degree of control of the biodeterioration processes of the lithic substrate and reducing the chances of subsequent lichen recolonization.

Foliicolous lichens are formed by diverse, highly specialized fungi that establish themselves and complete their life cycle within the brief duration of their leaf substratum. Over half of these lichen-forming fungi are members of either the Gomphillaceae or Pilocarpaceae, and associate with Trebouxia-like green algae whose identities have never been positively determined. We investigated the phylogenetic affinities of these photobionts to better understand their role in lichen establishment on an ephemeral surface. Thallus samples of Gomphillaceae and Pilocarpaceae were collected from foliicolous communities in southwest Florida and processed for sequencing of photobiont marker genes, algal cultivation and/or TEM. Additional specimens from these families and also from Aspidothelium (Thelenellaceae) were collected from a variety of substrates globally. Sequences from rbcL and nuSSU regions were obtained and subjected to Maximum Likelihood and Bayesian analyses. Analysis of 37 rbcL and 7 nuSSU algal sequences placed all photobionts studied within the provisional trebouxiophycean assemblage known as the Watanabea clade. All but three of the sequences showed affinities within Heveochlorella, a genus recently described from tree trunks in East Asia. The photobiont chloroplast showed multiple thylakoid stacks penetrating the pyrenoid centripetally as tubules lined with pyrenoglobuli, similar to the two described species of Heveochlorella. We conclude that Heveochlorella includes algae of potentially major importance as lichen photobionts, particularly within (but not limited to) foliicolous communities in tropical and subtropical regions worldwide. The ease with which they may be cultivated on minimal media suggests their potential to thrive free-living as well as in lichen symbiosis.

Foliicolous lichens complete their life cycles upon non-deciduous leaves in humid tropical and subtropical environments. The anatomy of these lichens and its adaptations to this specialized niche have received only limited attention. The present work examines the structural organization in seven species of the Gomphillaceae that colonize palm leaves in south-west Florida, USA. Thalli with their leaf substratum were embedded in resin and examined with SEM in backscattered electron detection mode. All species showed a continuous, covering epilayer of fungal origin that consisted of relatively sparse, scattered cell lumina of reduced diameter connected by cell wall-derived material. Fungal cells were intermixed below this layer, with algal cells often resting directly on the substratum. Interactions between symbionts were mainly limited to wall-to-wall contacts without penetration. The epilayer showed continuity with the fungal prothallus at the perimeter of the thalli. Crystalline deposits in the upper portions of thalli were common, particularly in the species of Gyalectidium examined. All thalli were entirely epicuticular; some covered the stomata of the leaf beneath. It is suggested that the prominence of non-living wall materials and mineral crystals in thallus structure might serve to minimize the metabolic cost of fungal tissue in climates where warm temperatures at night result in higher rates of respiration.

The cyanobacterium Microcystis aggregates into colonies with a mucilaginous sheath that constitutes a special microhabitat for many microorganisms that associate to it. Here, we examine the notorious, yet scarcely studied case of epiphytic association by the cyanobacterium Pseudanabaena sp. to colonial Microcystis. Co-cultivation of Pseudanabaena with different Microcystis strains evidenced strong specificity in the interaction, with dramatically different outcomes in each case, including (1) inability of Pseudanabaena to access the slime of Microcystis, (2) neutral co-existence of epiphytic Pseudanabaena and Microcystis, and (3) rapid epiphytic proliferation of Pseudanabaena, followed by lysis and rapid decay of Microcystis cells. Whereas strain-specific oligopeptide production could not explain the observed specificity, differences in slime microstructures among Microcystis strains revealed by low-temperature scanning electron microscopy suggest that slime structural features might initially determine the ability of Pseudanabaena to colonize Microcystis, subsequently driving the outcome of the interaction. Furthermore, even under “neutral” co-existence, Pseudanabaena proliferation results in an increase in density that leads to colony settling, implying potential selective losses under natural conditions. Both the selective and antagonistic characters of the interaction indicate that epiphytic Pseudanabaena have the potential to contribute to the dynamics of strains in natural Microcystis communities.