Participación microbiana en la formación de magnesita dentro de un ambiente lacustre evaporítico: Mioceno de la Cuenca de Madrid

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEBanco de Santanderpu

Magnesite formation by microbial activity: Evidence from a Miocene hypersaline lake

This paper provides an ancient analogue for biologically mediated magnesite in lacustrine hypersaline environments. Thin beds of massive to crudely laminated magnesitic marls occur interbedded with mudstone and evaporite facies deposited in a saline lake-mudflat sedimentary system during the Lower Miocene in the Madrid Basin, Central Spain. Exposure of this succession in a recently excavated tunnel and in collected cores offered a good opportunity to study magnesite precipitates that have been preserved in unaltered conditions by primary evaporitic minerals. Specifically, magnesite arranged as host matrix between and enclosed by displacive halite and glauberite crystals occurs closely associated with abundant microfossils embedded in sheets of organic matter, interpreted as the remains of extracellular polymeric substances (EPS). Even, many magnesite clots are seen to have resulted from the agglutination of fossilized bacterial bodies forming a biofilm. The close and pervasive association of microorganisms and magnesite is used as evidence that microbes played a fundamental role in the precipitation of this mineral. Additional traces of microorganisms and microbial activity observed in magnesite beds include the isotopic ratios in the carbonates, with the δ13C(PDB) value averaging −6.2‰, the presence of carbonaceous film-like structures and the association with patchly-distributed pyrite and celestite minerals. On the basis of the combined sedimentological, mineralogical, chemical and morphological signatures of the magnesitic deposits, it is postulated that carbonate crystals precipitated in microbial mats. Magnesite crystals together with celestite, local barite, and/or pyrite have been also observed to replace silicate and sulphate minerals. It is suggested that magnesite precipitation was biochemically coupled with the early dissolution of the associated sedimentary minerals. Microbes may have used the associated minerals as source of energy and/or of essential elements

Endomycorrhizae in Miocene paleosols: Implications in biotite weathering and accumulation of dolomite in plant roots (SW Madrid Basin, Spain)

This work provides evidence of arbuscular mycorrhizae (or endomycorrizhae) and their role in mineral weathering and soil carbonate production from Miocene paleosols. Formation of the paleosols-bearing mycorrhizae took place in marginal lacustrine and distal-fan deposits in the Madrid Basin. Endomycorrizhae fossils are preserved as carbonate in biotite-filled rhizoliths. Fossilized mycorrhizae are morphologically identical to those of living counterparts and consist of two linked parts. The extraradicular segment surrounding the root is represented by a calcitic mycelium comprising spores and two types of hyphae that are seen to attach and to corrode the mineral grains. The intraradicular part is made of a network of branched filaments, hyphal coils, arbuscules and likely vesicles that are mixed with the cortical root cells of the plants fossilized as dolomicrosparite aggregates. The preferential formation of the dolomite aggregates on biotite grains in rhizoliths is interpreted to reflect a focused interest of the plants on this mineral and indicates the mineral may have been used as a source of plant nutrients. The close association of the carbonate with the silicate further suggests that the precipitation of dolomite in the root cells and the weathering of the biotite resulted from interrelated processes. Main mechanisms to produce mineral dissolution include organic acids and chelate secretions by the plant roots and fungi which would remove nutrients. These results confirm that carbonate paleosols provide an excellent reservoir of information on ecological interactions and biogeochemical cycling, and expand the range of biogenic processes and their resultant products involved in the formation of carbonate soils. This approach has broad applications given the abundance of carbonate paleosols and the endomycorrhiza record dating back 400 million years

The role of microbial mats in the movement of stones on playa lake surfaces

This paper sheds light into the debated mechanisms that move rocks across low gradient surfaces during storm episodes. Microbial mats are recognised to play a crucial role in sediment destabilisation and the subsequent motion of rocks in a playa lake from central Spain. Widespread countless scars are present on the playa lake sediment surface, each terminating at a stone, and/or a mound of overfolded fragments of microbial mats. All available objects, including cobble-sized stones, on the surface were transported for several metres leaving behind furrow-like tracks. The starting point of the trackswas found underwater on a surface veneered by microbial mats poorly attached to the substrate. The flotation and transportation of the microbial upper layer by wind-generatedwater currents are suggested to be a critical element promoting the destabilisation and subsequent transportation of the attached sediment, including the rocks. The sudden exposure of bubble-separated sediment is also envisaged as a source of buoyancy required to lift out the rocks at the starting point of the tracks and to reduce the friction on the base of the rock. At the end of the tracks the rocks and the sedimentmounds often overlap,which reveals that rockswere embedded and transported by sediment rafts across the playa lake surface. The combination of the specific sedimentary and weather conditions involved in the transportation of rocks occurs periodically in mudflats. The implications are that this is not a local phenomenon, but rather, is a geographically widespread sedimentary process that may have occurred repeatedly throughout geological time. The effects of storm episodes can be inferred in ancient mudflat deposits by the assemblage of variablysized stones and microbial-mat related structures

Silicate bioweathering and biomineralization in lacustrine microbialites: ancient analogues from the Miocene Duero Basin, Spain

The Miocene dolomite-chert microbialites studied here offer a complete record of the geochemical cycles of silicate weathering and the subsequent formation of secondary products. The microbialites were formed in lacustrine systems during the Miocene of the Duero Basin, central Spain. Mineralogical, chemical and petrographic results provide evidence of the mediation of microbes in early weathering and by-product formation processes. Irrespective of the composition, the surfaces of the grains were subject to microbial attachment and concomitant weathering. Palaeo-weathering textures range from surface etching and pitting to extensive physical disaggregation of the minerals. Extreme silicate weathering led to the complete destruction of the silicate grains, whose prior existence is inferred from pseudomorphs exhibiting colonial textures like those recognized in the embedding matrix. Detailed petrographic and microanalytical examinations of theweathering effects in K-feldspars show that various secondary products with diverse crystallinity and chemical composition can coexist in the interior of a mineral. The coexistence of by-products is indicative of different microenvironmental conditions, likely created by microbial reactions. Thus, the presence of varied secondary products can be used as a criterion of biogenicity. Intensive alteration of P-bearing feldspars suggests that mineral weathering may have been driven by the nutrient requirements of the microbial consortium involved in the precipitation of dolomite. The rock record provides useful information on mineral weathering mediated by microbes

Tgfβ2 and 3 are coexpressed with their extracellular regulator Ltbp1 in the early limb bud and modulate mesodermal outgrowth and BMP signaling in chicken embryos

<p>Abstract</p> <p>Background</p> <p>Transforming growth factor β proteins (Tgfβs) are secreted cytokines with well-defined functions in the differentiation of the musculoskeletal system of the developing limb. Here we have studied in chicken embryos, whether these cytokines are implicated in the development of the embryonic limb bud at stages preceding tissue differentiation.</p> <p>Results</p> <p>Immunohistochemical detection of phosphorylated Smad2 and Smad3 indicates that signaling by this pathway is active in the undifferentiated mesoderm and AER. Gene expression analysis shows that transcripts of <it>tgfβ2 </it>and <it>tgfβ3 </it>but not <it>tgfβ1 </it>are abundant in the growing undifferentiated limb mesoderm. Transcripts of <it>tgfβ2 </it>are also found in the AER, which is the signaling center responsible for limb outgrowth. Furthermore, we show that Latent Tgfβ Binding protein 1 (LTBP1), which is a key extracellular modulator of Tgfβ ligand bioavailability, is coexpressed with <it>Tgfβs </it>in the early limb bud. Administration of exogenous Tgfβs to limb buds growing in explant cultures provides evidence of these cytokines playing a role in the regulation of mesodermal limb proliferation. In addition, analysis of gene regulation in these experiments revealed that Tgfβ signaling has no effect on the expression of master genes of musculoskeletal tissue differentiation but negatively regulates the expression of the BMP-antagonist Gremlin.</p> <p>Conclusion</p> <p>We propose the occurrence of an interplay between Tgfβ and BMP signaling functionally associated with the regulation of early limb outgrowth by modulating limb mesenchymal cell proliferation.</p

Confluence of Cellular Degradation Pathways During Interdigital Tissue Remodeling in Embryonic Tetrapods

Digits develop in the distal part of the embryonic limb primordium as radial prechondrogenic condensations separated by undifferentiated mesoderm. In a short time interval the interdigital mesoderm undergoes massive degeneration to determine the formation of free digits. This fascinating process has often been considered as an altruistic cell suicide that is evolutionarily-regulated in species with different degrees of digit webbing. Initial descriptions of interdigit remodeling considered lysosomes as the primary cause of the degenerative process. However, the functional significance of lysosomes lost interest among researcher and was displaced to a secondary role because the introduction of the term apoptosis. Accumulating evidence in recent decades has revealed that, far from being a unique method of embryonic cell death, apoptosis is only one among several redundant dying mechanisms accounting for the elimination of tissues during embryonic development. Developmental cell senescence has emerged in the last decade as a primary factor implicated in interdigit remodeling. Our review proposes that cell senescence is the biological process identified by vital staining in embryonic models and implicates lysosomes in programmed cell death. We review major structural changes associated with interdigit remodeling that may be driven by cell senescence. Furthermore, the identification of cell senescence lacking tissue degeneration, associated with the maturation of the digit tendons at the same stages of interdigital remodeling, allowed us to distinguish between two functionally distinct types of embryonic cell senescence, "constructive" and "destructive."This work was supported by a grant (BFU2017-84046-P) from the Spanish Science and Innovation Ministry to JM

Activin/TGFβ and BMP crosstalk determines digit chondrogenesis

AbstractThe progress zone (PZ) is a specialized area at the distal margin of the developing limb where mesodermal cells are kept in proliferation and undifferentiated, allowing limb outgrowth. At stages of digit morphogenesis the PZ cells can undergo two possible fates, either aggregate initiating chondrogenic differentiation to configure the digit blastemas, or to die by apoptosis if they are incorporated in the interdigital mesenchyme. While both processes are controlled by bone morphogenetic proteins (BMPs) the molecular basis for such contrasting differential behavior of the autopodial mesoderm remains unknown. Here we show that a well-defined crescent domain of high BMP activity located at the tip of the forming digits, which we termed the digit crescent (DC), directs incorporation and differentiation of the PZ mesenchymal cells into the digit aggregates. The presence of this domain does not correlate with an exclusive expression domain of BMP receptors and its abrogation by surgical approaches or by local application of BMP antagonists is followed by digit truncation and cell death. We further show that establishment of the DC is directed by Activin/TGFβ signaling, which inhibits Smad 6 and Bambi, two specific BMP antagonists expressed in the interdigits and progress zone mesoderm. The interaction between Activin/TGFβ and BMP pathways at the level of DC promotes the expression of the chondrogenic factor SOX9 accompanied by a local decrease in cell proliferation. Characteristically, the DC domain is asymmetric, it being extended towards the posterior interdigit. The presence of the DC is transitorily dependent of the adjacent posterior interdigit and its maintenance requires also the integrity of the AER

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