Endolithic Microorganisms Research Articles

Adaptation of the Endolithic Biome in Antarctic Volcanic Rocks.

Endolithic microorganisms, ranging from microeukaryotes to bacteria and archaea, live within the cracks and crevices of rocks. Deception Island in Antarctica constitutes an extreme environment in which endoliths face environmental threats such as intense cold, lack of light in winter, high solar radiation in summer, and heat emitted as the result of volcanic eruptions. In addition, the endolithic biome is considered the harshest one on Earth, since it suffers added threats such as dryness or lack of nutrients. Even so, samples from this hostile environment, collected at various points throughout the island, hosted diverse and numerous microorganisms such as bacteria, fungi, diatoms, ciliates, flagellates and unicellular algae. These endoliths were first identified by Scanning Electron Microscopy (SEM). To understand the molecular mechanisms of adaptation of these endoliths to their environment, genomics techniques were used, and prokaryotic and eukaryotic microorganisms were identified by metabarcoding, sequencing the V3-V4 and V4-V5 regions of the 16S and 18S rRNA genes, respectively. Subsequently, the sequences were analyzed by bioinformatic methods that allow their metabolism to be deduced from the taxonomy. The results obtained concluded that some of these microorganisms have activated the biosynthesis routes of pigments such as prodigiosin or flavonoids. These adaptation studies also revealed that microorganisms defend themselves against environmental toxins by activating metabolic pathways for the degradation of compounds such as ethylbenzene, xylene and dioxins and for the biosynthesis of antioxidant molecules such as glutathione. Finally, these Antarctic endolithic microorganisms are of great interest in astrobiology since endolithic settings are environmentally analogous to the primitive Earth or the surfaces of extraterrestrial bodies.

Dispersal of endolithic microorganisms in vesicular volcanic rock: Distribution, settlement and pathways revealed by 3D X‐ray microscopy

AbstractPleistocene basanitic rocks of Vesteris Seamount in the Greenland Sea had been found to exhibit an endolithic habitat largely consisting of marine fungi that dwell within abundant vesicles, therefore representing cryptoendoliths. For the first time, we demonstrate that 3D X‐ray microscopy can unravel how microorganisms access and migrate through vesicular rock. The fossil assemblages occur within a set of vesicles connected by microcracks. Such microcracks, which are ubiquitous features in submarine volcanic rocks, enable the dispersal of marine microorganisms in the rock. This study suggests that this pathway for the colonization of marine volcanic rocks forms in consequence of early tensional stress due to variable rates of cooling of the lava flow. Subsequently, the interconnected vesicles get populated by rock‐dwelling microorganisms. This cryptoendolithic habitat exists at least since the Paleoproterozoic.

Statistical trends in culture methods of endolithic bacteria extracted from Quartz, K-Feldspar (Jurassic) and Calcite (Quaternary) in semi-arid areas in Colombia

Microbial endolithic communities are ubiquitous in many deserts around the globe. They have been found in many different lithologies, including quartz, plagioclase and calcite. The use of culture methods in geomicrobiology is important because most bacteria are non-cultivable, which makes it very difficult to characterize and describe them. In this study, endolithic bacteria and yeast were cultured in three rock-forming minerals (quartz, K-feldspar and calcite) with standard culture methodologies. It was demonstrated that these endolithic microorganisms could grow in noble agar enriched with a mineral different from the one they were extracted. Microbes were also cultured in a nutritive broth under some physicochemical factors (sugar, salt, pH and temperature) to study their possible tolerance to different ecological conditions. These results were combined with Multiple Factorial Analysis to identify statistical trends between their morphologies (pigment, size and Gram stain), chemical elements and their tolerance to physicochemical factors. Our results show that it might exist a relationship between pigments in microbial colonies,their tolerance to pH9, salinity and temperature conditions; and that Gram-negative bacillus might have a high adaptive ability to different enriched minimum media. Characterizing microbial communities associated with lithic substrates in the laboratory could be helpful for future planning in the search for life on Mars.

Depth wide distribution and metabolic potential of chemolithoautotrophic microorganisms reactivated from deep continental granitic crust underneath the Deccan Traps at Koyna, India.

Characterization of inorganic carbon (C) utilizing microorganisms from deep crystalline rocks is of major scientific interest owing to their crucial role in global carbon and other elemental cycles. In this study we investigate the microbial populations from the deep [up to 2,908 meters below surface (mbs)] granitic rocks within the Koyna seismogenic zone, reactivated (enriched) under anaerobic, high temperature (50°C), chemolithoautotrophic conditions. Subsurface rock samples from six different depths (1,679-2,908 mbs) are incubated (180 days) with CO2 (+H2) or HCO3 - as the sole C source. Estimation of total protein, ATP, utilization of NO3 - and SO4 2- and 16S rRNA gene qPCR suggests considerable microbial growth within the chemolithotrophic conditions. We note a better response of rock hosted community towards CO2 (+H2) over HCO3 -. 16S rRNA gene amplicon sequencing shows a depth-wide distribution of diverse chemolithotrophic (and a few fermentative) Bacteria and Archaea. Comamonas, Burkholderia-Caballeronia-Paraburkholderia, Ralstonia, Klebsiella, unclassified Burkholderiaceae and Enterobacteriaceae are reactivated as dominant organisms from the enrichments of the deeper rocks (2335-2,908 mbs) with both CO2 and HCO3 -. For the rock samples from shallower depths, organisms of varied taxa are enriched under CO2 (+H2) and HCO3 -. Pseudomonas, Rhodanobacter, Methyloversatilis, and Thaumarchaeota are major CO2 (+H2) utilizers, while Nocardioides, Sphingomonas, Aeromonas, respond towards HCO3 -. H2 oxidizing Cupriavidus, Hydrogenophilus, Hydrogenophaga, CO2 fixing Cyanobacteria Rhodobacter, Clostridium, Desulfovibrio and methanogenic archaea are also enriched. Enriched chemolithoautotrophic members show good correlation with CO2, CH4 and H2 concentrations of the native rock environments, while the organisms from upper horizons correlate more to NO3 -, SO4 2- , Fe and TIC levels of the rocks. Co-occurrence networks suggest close interaction between chemolithoautotrophic and chemoorganotrophic/fermentative organisms. Carbon fixing 3-HP and DC/HB cycles, hydrogen, sulfur oxidation, CH4 and acetate metabolisms are predicted in the enriched communities. Our study elucidates the presence of live, C and H2 utilizing Bacteria and Archaea in deep subsurface granitic rocks, which are enriched successfully. Significant impact of depth and geochemical controls on relative distribution of various chemolithotrophic species enriched and their C and H2 metabolism are highlighted. These endolithic microorganisms show great potential for answering the fundamental questions of deep life and their exploitation in CO2 capture and conversion to useful products.

Amplicon Sequencing of Rock-Inhabiting Microbial Communities from Joshua Tree National Park, USA.

ABSTRACTEndolithic microorganisms have been reported to date in hot and cold drylands worldwide, where they represent the prevailing life forms ensuring ecosystem functionality, playing a paramount role in global biogeochemical processes. We report here an amplicon sequencing characterization of rocks collected from Joshua Tree National Park (JTNP), USA.

Fossilized Endolithic Microorganisms in Pillow Lavas from the Troodos Ophiolite, Cyprus

The last decade has revealed the igneous oceanic crust to host a more abundant and diverse biota than previously expected. These underexplored rock-hosted deep ecosystems dominated Earth’s biosphere prior to plants colonized land in the Ordovician, thus the fossil record of deep endoliths holds invaluable clues to early life and the work to decrypt them needs to be intensified. Here, we present fossilized microorganisms found in open and sealed pore spaces in pillow lavas from the Troodos Ophiolite (91 Ma) on Cyprus. A fungal interpretation is inferred upon the microorganisms based on characteristic morphological features. Geochemical conditions are reconstructed using data from mineralogy, fluid inclusions and the fossils themselves. Mineralogy indicates at least three hydrothermal events and a continuous increase of temperature and pH. Precipitation of 1) celadonite and saponite together with the microbial introduction was followed by 2) Na and Ca zeolites resulting in clay adherence on the microorganisms as protection, and finally 3) Ca carbonates resulted in final fossilization and preservation of the organisms in-situ. Deciphering the fossil record of the deep subseafloor biosphere is a challenging task, but when successful, can unlock doors to life’s cryptic past.

Intricate tunnels in garnets from soils and river sediments in Thailand - Possible endolithic microborings.

Garnets from disparate geographical environments and origins such as oxidized soils and river sediments in Thailand host intricate systems of microsized tunnels that significantly decrease the quality and value of the garnets as gems. The origin of such tunneling has previously been attributed to abiotic processes. Here we present physical and chemical remains of endolithic microorganisms within the tunnels and discuss a probable biological origin of the tunnels. Extensive investigations with synchrotron-radiation X-ray tomographic microscopy (SRXTM) reveal morphological indications of biogenicity that further support a euendolithic interpretation. We suggest that the production of the tunnels was initiated by a combination of abiotic and biological processes, and that at later stages biological processes came to dominate. In environments such as river sediments and oxidized soils garnets are among the few remaining sources of bio-available Fe2+, thus it is likely that microbially mediated boring of the garnets has trophic reasons. Whatever the reason for garnet boring, the tunnel system represents a new endolithic habitat in a hard silicate mineral otherwise known to be resistant to abrasion and chemical attack.

Life in Extreme Habitats: Diversity of Endolithic Microorganisms from Cold Desert Ecosystems of Eastern Pamir

ABSTRACT The aim of this study was to identify cyanobacteria diversity in rock communities from the cold desert ecosystem in Eastern Pamir Mountains (Tajikistan) and assess if the rock type and rock`s porosity can be indicators of microbial diversity in this extreme environment. Seven samples were collected in July 2015 from hillsides (ca 4000–4500 m a.s.l.) of the Eastern Pamir Mountains. Petrographic and scanning microscopy (SEM) allowed for the characterization of the rocks inhabited by endolithic communities as granite, gneiss and limestone with variable porosity. Based on next-generation sequencing (NGS) of amplicon of V3–V4 hypervariable region of 16S rRNA gene, we established that Actinobacteria, Proteobacteria and Cyanobacteria dominated the endolithic communities of microorganisms in the rocks studied, which distinguishes these communities from those described for other cold arid regions. Chroococcidiopsis and Leptolyngbya were dominant genera in the cyanobacterial communities according to cultur...

Ambient inclusion trails and microboring structures on Early Cambrian microfossils

Ambient inclusion trails (AITs) are microtubular structures on various substrates that have occurred widely through the geologic record. They are thought to be generated by the migration of inclusion grains (pyrite, magnetite, carbonaceous spherules), termed ″terminal propelled grains″, through a substrate driven by pressure solution from the in situ thermal decomposition of organic matter. AITs have been reported frequently from Archean rocks, and also commonly occurring with phosphatized fossils through late Neoproterozoic and Cambrian. During this timeframe, bioturbation was also becoming more intense, and some analogous, AIT-like structures may be more appropriately interpreted as endolithic micro-organisms or borings of predatory animals. It is thus crucial to reduce potential ambiguity between these types of structures, and provide keys for distinguishing AITs and real biogenic structures. From the Early Cambrian Kuanchuanpu Fm. in Xixiang, Southern Shaanxi, China, numerous microfossils hosting AITs were collected and examined, with recognition of two types of co-occurring micro-borings in addition to AITs. Type 1 micro-boring structures appear as long, unbranched, cylindrical filaments with isodiametric spheroidal expansions on the surface of steinkerns or moulds of small shelly fossils (SSFs); these structures correlate well with casts of known endolithic cyanobacterial fossils, Endoconchia lata . Type 2 micro-boring structures are comprised of dense networks of microborings and microtunnels on the phosphatized fossil materials, and are interpreted as trace fossils of endolithic fungi. Such a co-occurrence enables us to make direct comparisons between the variations in microtubular structures. We have made detailed observations of their morphological and taphonomic features, which collectively reveal that they are substantially different in both formation and mechanism of preservation. In the initial stage of formation of Type 1 structures, E. lata bored within the original calcite shells of SSFs, with the resulting borings preserved as phosphatic casts during phosphatization. Type 2 structures were caused by infestation of endolithic fungi on the phosphatized fossils while there were still much residual organic materials available for their probably heterotrophic life mode, leaving dense traces of boring behavior. With deeper burial and occurring later in the taphonomic sequence, thermal decomposition of the surrounding organic remains released gases that propelled small inclusions to move through the substrates, forming AIT tunnels. Some peculiar spherical grains preserved in the distal ends of AITs have been discovered and examined with Laser-Raman and EDS mapping. These data revealed that organic carbon is their major component. The intact spherical profiles without evidence of compression in their tunnel-facing backsides, and the perfect fit of the grain margins and AIT outlines suggest that these carbonaceous grains may have themselves been responsible for AIT formation rather than passive accumulation or secondary filling. Such rare carbonaceous terminal propelled grains of AITs not only explains the morphological diversity (rounded cross sections) of AIT tunnels, but also provide us with a new approach to investigate the taphonomic environment of the fossil-enriched strata. Raman geothermometry of these carbonaceous materials indicates that the Kuanchuanpu Fm. in this area underwent very low-grade metamorphism, with a peak metamorphic temperature estimated at 232–261°C. This implies that the fossils are mostly free from metamorphic overprints, and roughly constrains the upper limits of AIT formation. In general, as indirectly biogenic structures, the distribution of AITs is random and shows no preference for fossil taxonomy and no particular pattern. However, for those AITs that occurred on protoconodonts, there is an intriguing distribution pattern that AITs traveled around the outskirts of protoconodont spines, forming distinctive spiral grooves. Such a phenomenon may provide auxiliary evidence of their original composition by the following interpretations. The half-open grooves indicate the original composition of protoconodont spines were relatively soft material as opposed to hard bioapatite. The polygonal cross sections suggest, in this case, that the propelled grains were euhedral pyrite crystals, which were usually resulted by the decomposition of more recalcitrant organic materials. Our interpretation is that euhedral pyrite crystals moved from inside of the spines and were trapped by surrounding hard substrate, forming spiral grooves on the fossil-sediment interface. Our observations are consistent with the hypothesis that the original composition of the protoconodont spines are mainly organic, such as chitin, with secondary phosphatization—this hypothesis presents a more favorable scenario for the observed morphologies of the AITs formed by migration of euhedral pyrite crystals through a relatively soft substrate.

Diversity and stability of coral endolithic microbial communities at a naturally high pCO2 reef.

The health and functioning of reef-building corals is dependent on a balanced association with prokaryotic and eukaryotic microbes. The coral skeleton harbours numerous endolithic microbes, but their diversity, ecological roles and responses to environmental stress, including ocean acidification (OA), are not well characterized. This study tests whether pH affects the diversity and structure of prokaryotic and eukaryotic algal communities associated with skeletons of Porites spp. using targeted amplicon (16S rRNA gene, UPA and tufA) sequencing. We found that the composition of endolithic communities in the massive coral Porites spp. inhabiting a naturally high pCO2 reef (avg. pCO2 811μatm) is not significantly different from corals inhabiting reference sites (avg. pCO2 357μatm), suggesting that these microbiomes are less disturbed by OA than previously thought. Possible explanations may be that the endolithic microhabitat is highly homeostatic or that the endolithic micro-organisms are well adapted to a wide pH range. Some of the microbial taxa identified include nitrogen-fixing bacteria (Rhizobiales and cyanobacteria), algicidal bacteria in the phylum Bacteroidetes, symbiotic bacteria in the family Endozoicomoniaceae, and endolithic green algae, considered the major microbial agent of reef bioerosion. Additionally, we test whether host species has an effect on the endolithic community structure. We show that the endolithic community of massive Porites spp. is substantially different and more diverse than that found in skeletons of the branching species Seriatopora hystrix and Pocillopora damicornis. This study reveals highly diverse and structured microbial communities in Porites spp. skeletons that are possibly resilient to OA.

The Study of Growth of Calogaya sp. PLM8 on Cyrus the Great’s Tomb, UNESCO World Heritage Site in Iran

The tomb of Cyrus the Great, the most important monument in Pasargadae, has been listed as a world heritage site by UNESCO. Like many other stone monuments, the tomb has been affected by the colonization of microbial communities, especially lichens that were subjected to physical elimination in 2006. In the present study, recolonization of Calogaya sp. PLM8, a crustose lichen and its role in biodeterioration of Cyrus the Great tomb have been evaluated. Calogaya sp. PLM8 commonly colonized on this monument with significant distribution in the different facades. The interface of Calogaya sp. PLM8 with the underlying substrate has been investigated using the periodic acid-Schiff staining, scanning electron microscopy and energy-dispersive spectroscopy techniques. The results showed that both colonization of the lichen on the surface and symbiont cells penetration into the stone had caused extensive physical and chemical biodeterioration of the substrate. Besides the presence of the symbionts in the endolithic niches, other lithobiont microorganisms have been detected inside the stones. The presence of these endolithic microorganisms seems to be conditioned by the presence of the epilithic lichen thallus and its effects on the formation of microenvironments in the colonized stone. The lithobiont communities interact both geophysically and geochemically with the lithic substrate, inducing biodeterioration alteration in the tomb of Cyrus the Great.

Microbial Endoliths on East Adriatic Limestone Coast: Morphological vs. Molecular Diversity

ABSTRACTFor the first time, a combined genotype-phenotype diversity analysis of endolithic microorganisms by pyrosequencing and microscopy was carried out across the intertidal and supratidal ranges of the Adriatic limestone coast. The coastal profiles represent ecotones between the sea and land, which express gradients of water supply, solar illumination, and salinity. The use of scanning electron microscopy imagery of resin casts showed that euendolith penetration remained shallow in the uppermost zones and was progressively deeper in the lower ranges where the water supply was more frequent. Microbial genotypes and phenotypes along the coastal profile showed large differences in dominance of taxa, but less in their diversity. The linkage between morphotypes observed along the profile and sequences was achieved by sequencing single cells/filaments, which were morphologically identified prior to their amplification. Molecular signatures of Hormathonema spp., Hyella caespitosa, Scytonema endolithicum, Solentia paulocellulare and Kyrtuthrix dalmatica were found on the profile and their specific placement was confirmed by morphological observations. Most sequences obtained were affiliated with Cyanobacteria (43%), Alphaproteobacteria (18%), and Gammaproteobacteria (7%). A total of 13 cyanobacterial morphospecies and 17 genotypes were found. Most cyanobacterial sequences belonged to the Pleurocapsales (33%), only 2% of the sequences belonged to the Nostocales and Oscillatoriales. The sequences corresponding to the cyanobacterial genus Hormathonema exhibited the highest abundances among all detected sequences, which is consistent with the microscopic observations in other parts of the world. The results of our investigation underline the importance of a combined approach in comparing the molecular data with microscopic observations in all phases of the study. Further RNA studies are needed to identify the actively growing parts of the endolithic community.

Euendolithic Conchocelis stage (Bangiales, Rhodophyta) in the skeletons of live stylasterid reef corals

Stylasterids are azooxanthellate lace corals, which may show an unusual colouration in coral reef ecosystems, ranging from red to purple on the light-exposed side of their colonies. In the present study, it was discovered that the calcareous skeletons of such corals are actually invaded and eroded by cryptic carbonate boring algae that represent Conchocelis phases in the life cycle of bangialean rhodophytes. For the first time, the shape, organisation and distribution of Conchocelis filaments within the skeletons of two different genera of lace corals are reported and documented by light and electron microscopy. Such description and characterisation of Conchocelis can help to distinguish between morphologically and taxonomically different endolithic microorganisms penetrating coral skeletons, including their recognition in fossil borings as indicators of depositional depth, i.e. of the extent of the photic zone and light conditions in ancient marine environments. The results are discussed in the light of a possible symbiotic or parasitic relationship between Conchocelis phases and their stylasterid host corals.

Survival, DNA Integrity, and Ultrastructural Damage in Antarctic Cryptoendolithic Eukaryotic Microorganisms Exposed to Ionizing Radiation.

Life dispersal between planets, planetary protection, and the search for biosignatures are main topics in astrobiology. Under the umbrella of the STARLIFE project, three Antarctic endolithic microorganisms, the melanized fungus Cryomyces antarcticus CCFEE 515, a hyaline strain of Umbilicaria sp. (CCFEE 6113, lichenized fungus), and a Stichococcus sp. strain (C45A, green alga), were exposed to high doses of space-relevant gamma radiation (60Co), up to 117.07 kGy. After irradiation survival, DNA integrity and ultrastructural damage were tested. The first was assessed by clonogenic test; viability and dose responses were reasonably described by the linear-quadratic formalism. DNA integrity was evaluated by PCR, and ultrastructural damage was observed by transmission electron microscopy. The most resistant among the tested organisms was C. antarcticus both in terms of colony formation and DNA preservation. Besides, results clearly demonstrate that DNA was well detectable in all the tested organisms even when microorganisms were dead. This high resistance provides support for the use of DNA as a possible biosignature during the next exploration campaigns. Implication in planetary protection and contamination during long-term space travel are put forward. Key Words: Biosignatures-Ionizing radiation-DNA integrity-Eukaryotic microorganisms-Fingerprinting-Mars exploration. Astrobiology 17, 126-135.

Epilithic and endolithic microorganisms and deterioration on stone church facades subject to urban pollution in a sub-tropical climate

Weathering of two church facades in Rio de Janeiro was caused substantially by salts, mainly halite and gypsum, detected by SEM and chemical analyses, which cause physical stresses by deposition within the rock. Biofilm populations, determined by SEM and as operational taxonomic units (OTUs), degraded stone by penetration, solubilization and redeposition of minerals on their surfaces. Endolithic cyanobacteria were associated with gypsum deposits. Microbiomes were typical for high-stress environments, high salt, intense insolation, low water and low nutrients (eg halophilic Rubrobacter, Salinicola, Sterigmatomyces). The main colonizers on the church most affected by traffic (Nossa Senhora da Candelária – CA) were Actinobacteria; Gammaproteobacteria (chiefly Pseudomonas) were predominant on the site situated in a leafy square (São Francisco de Paula – SF). Major Gammaproteobacteria on CA were halophilic Halomonas and Rhodobacteriaceae. Fungal OTUs on both churches were principally dimorphic, yeast-like basidiomycetes. Many OTUs of thermophilic microorganisms (eg the Thermomicrobia class, Chloroflexi) were present. This is the first use of next generation sequencing (NGS) to study microbial biofilm interactions with metamorphic and granite buildings in an intensely urban, sub-tropical climate.

Prevalence of potential nitrogen‐fixing, green sulfur bacteria in the skeleton of reef‐building coral Isopora palifera

AbstractMicrobial endoliths, which inhabit interior pores of rocks, skeletons and coral, are ubiquitous in terrestrial and marine environments. In this study, various colored layers stratified the endolithic environment within the skeleton of Isopora palifera; however, there was a distinct green‐pigmented layer in the skeleton (beneath the living coral tissue). To characterize diversity of endolithic microorganisms, 16S ribosomal RNA gene amplicon pyrosequencing was used to investigate bacterial communities in the green layer of eight I. palifera coral colonies retrieved from two locations on Green Island, Taiwan. The dominant bacterial group in the green layer belonged to the bacterial phylum Chlorobi, green sulfur bacteria capable of anoxygenic photosynthesis and nitrogen fixation. Specifically, bacteria of the genus Prosthecochloris were dominant in this green layer. To our knowledge, this is the first study to provide a detailed profile of endolithic bacteria in coral and to determine the prevalence of Prosthecochloris in the green layer. Based on our findings, we infer that these bacteria may have an important functional role in the coral holobiont in the nutrient‐limited coral reef ecosystem.

Mapping the lithic colonization at the boundaries of life in Northern Victoria Land, Antarctica

The endolithic microbial communities of the Antarctic represent a borderline lifestyle in the most hostile ice-free areas of the continent. The extreme adaptation of microbes in these communities renders them very sensitive to environmental changes. To date, the actual distribution of these communities has never been investigated; yet, this information would define the geographic limits for life at present and supply a useful tool for monitoring any possible future variation related to climate change. In this study, most of the outcrops of Northern and of one site in Southern Victoria Land were recorded by altitudinal and sea distance gradients. The presence of endolithic life was determined by in situ observation, by microscopic observation of rock fragments in the laboratory, and, for doubtful samples, by culture experiment. Colonizers were present in more than 87 % of the visited sites. The presence of lithic life in Victoria Land appears to be wider than that reported 14 years earlier. The colonization trend follows climatic variation, with epiliths prevailing in coastal sites and decreasing towards the interior, while chasmoendoliths and cryptoendoliths increase and become predominant from the coast towards the inland sites. Typical cryptoendolithic colonization was exclusive on porous rocks as sandstone, chasmoendolithic colonization occurred even in less porous but translucent rocks as granite and quartz. Multivariate analysis of the combined results clearly indicates the pivotal role of the rock type in the colonization of endolithic micro-organisms; sandstone allows lithobionts to push themselves towards areas characterized by harsher conditions.

The Interlayer Regions of Sheet Silicates as a Favorable Habitat for Endolithic Microorganisms

Dark-colored rocks that attenuate photosynthetically active radiation (PAR) are generally thought to be poor substrates for endolithic colonization. In this study we show that the internal space of the common dark-colored mica mineral, biotite, is a favorable microhabitat for the growth of filamentous cyanobacteria. Laboratory incubation experiments demonstrated that filamentous cyanobacteria with a cell diameter of ≤3 μm were able to colonize biotite interlayers. Light transmittance measurements on solid biotite sheets showed that PAR (400–690 nm) transmission is sufficient to allow for cyanobacterial growth in the interlayer regions of the mineral. Of note is that damaging UV radiation is attenuated by more than one order of magnitude at the corresponding depth, most likely by the iron contained within the mineral, showing that the interlayer region represents a UV protected microhabitat with respect to the mineral surface. The interlayer region is therefore a favorable environment for small cells that cannot rely only on UV screening compounds. These results show that biotite, and by extension other layered silicate minerals, are a hitherto unrecognized habitat suitable for endolithic microorganisms with potential implications in research fields such as astrobiology.

Relative roles of endolithic algae and carbonate chemistry variability in the skeletal dissolution of crustose coralline algae

Abstract. The susceptibility of crustose coralline algae (CCA) skeletons to dissolution is predicted to increase as oceans warm and acidify. Skeletal dissolution is caused by bioerosion from endolithic microorganisms and by chemical processes associated with undersaturation of carbonate minerals in seawater. Yet, the relative contribution of algal microborers and seawater carbonate chemistry to the dissolution of organisms that cement reefs under projected pCO2 and temperature (pCO2-T) scenarios have not been quantified. We exposed CCA skeletons (Porolithon onkodes) to four pCO2-T treatments (pre-industrial, present-day, SRES-B1 "reduced" pCO2, and SRES-A1FI "business-as-usual" pCO2 emission scenarios) under natural light cycles vs. constant dark conditions for 8 weeks. Dissolution rates of skeletons without photo-endoliths were dramatically higher (200%) than those colonized by endolithic algae across all pCO2-T scenarios. This suggests that daytime photosynthesis by microborers counteract dissolution by reduced saturation states resulting in lower net erosion rates over day–night cycles. Regardless of the presence or absence of phototrophic microborers, skeletal dissolution increased significantly under the spring A1FI "business-as-usual" scenario, confirming the CCA sensitivity to future oceans. Projected ocean acidity and temperature may significantly disturb the stability of reef frameworks cemented by CCA, but surficial substrates harbouring photosynthetic microborers will be less impacted than those without algal endoliths.

Detection of endolithic spatial distribution in marble stone.

The penetration of endolithic microorganisms, which develop to depths of several millimetres or even centimetres into the stone, and the diffusion of their extracellular substances speeds up the stone deterioration process. The aim of this study was to investigate, using a confocal laser scanning microscopy with a double-staining, a marble rock sample by observing the endolithic spatial distribution and quantifying the volume they occupied within the stone, in order to understand the real impact of these microorganisms on the conservation of stone monuments. Often the only factors taken into account by biodeterioration studies regarding endolithic microorganisms, are spread and depth of penetration. Despite the knowledge of three-dimensional spatial distribution and quantification of volume, it is indispensable to understand the real damage caused by endolithic microorganisms to stone monuments. In this work, we analyze a marble rock sample using a confocal laser scanning microscopy stained with propidium iodide and Concavalin-A conjugate with the fluorophore Alexa Fluor 488, comparing these results with other techniques (SEM microscope, microphotographs of polished cross-sections and thin-section, PAS staining methods), An image analysis approach has also been applied. The use of confocal laser scanning microscopy with double staining shows clear evidence of the presence of endolithic microorganisms (cyanobacteria and fungi) as well as the extracellular polymeric substance matrix in a three-dimensional architecture as part of the rock sample, this technique, therefore, seems very useful when applied to restoration interventions on stone monuments when endolithic growth is suspected.