A significant fraction of Earth’s prokaryotic biomass is produced in the continental deep biosphere, but the exact size, diversity and evolution of this important habitat is still incompletely understood. In several studies, we targeted ancient microbial activity in the deep subsurface by analyzing inter alia the lipid biomarker content of fracture calcites. We detected fatty acids (mainly straight-chained and branched C_12:0 to C_20:0) of biological origin in calcites from various fracture systems of the continental crust (Fennoscandian and Greenlandic shields), including a broad depth interval (down to 1000 m) and different precipitation ages (back to 410 Ma; e.g., Drake et al., 2015, 2021, 2023, 2024). In locations where calcite co-occurred with pyrite, different branched C_15:0 and C_17:0 acids were found (e.g., Drake et al., 2018, 2021, 2023, 2024), which represent biomarkers of sulfate reducers. In addition, α,ω-diacids of unknown source were sometimes present. Based on our results, it seems that fatty acids are well preserved in facture calcites from the deep continental subsurface over long geological time scales. Such enhanced preservation likely derives from the physicochemical properties of the carboxyl groups of the fatty acids, matching those of Ca²⁺-ions on the calcite surface (e.g., Suess, 1970; Zullig and Morse, 1988). In addition, fatty acids and diacids may also serve as an initial nucleation site for calcite precipitation in the fractures, thereby being entrapped in the mineral lattice. Fracture calcite from the deep continental subsurface may therefore constitute an important archive for lipid biomarkers of ancient subsurface microorganisms.

A key innovation in the evolution of calcareous sponges was the ability to form calcite spicules. Several genes involved in this process have been characterized in the model organism Sycon ciliatum. These genes are expressed in active sclerocytes during different stages of spicule formation and are, in some cases, specific to certain spicule types. Many lack clear orthologs in other sponge classes, suggesting they represent genetic innovations dating back to the last common ancestor of extant Calcarea.

Here, we investigate the evolution of key biomineralization genes in Calcarea using genomic, transcriptomic, and proteomic data from both major subclasses, Calcinea and Calcaronea. Our results reveal that several of these genes are orthologous within Calcarea and absent from other sponge lineages. These findings support the growing body of evidence that spicule formation evolved multiple times independently in different sponge classes. Within Calcarea, gene innovation followed by duplication and neofunctionalization has refined the biomineralization toolkit, giving rise to spicule-type-specific functions.

Aquifer sediments, formed under varying depositional conditions, exhibit significant heterogeneity in their sedimentary architecture causing variability in their hydraulic and biogeochemical properties. The spatial arrangement of these properties controls the net turnover of biogeochemically reactive and environmentally relevant solutes in floodplains. However, the interlinkage between reactive and hydraulic properties is still enigmatic. This study proposes using sedimentary facies analyses to reconstruct the paleoenvironmental conditions that control the abundance and spatial distribution of aquifer materials, their potential as electron donors, and their hydraulic conductivity. The approach is applied to a Holocene aquifer in the Ammer floodplain in South-West Germany, which consists mainly of organic-rich tufa successions with varying contents of total organic carbon (TOC), peat lenses, as well as of gravel- and clay layers. The spatial extent of sedimentary features and baseline reactive properties (TOC, hydraulic conductivity) were constrained by combining sedimentological observations and bulk geochemical analyses. Based on the insights gained from the paleoenvironmental reconstruction, a facies-based virtual aquifer resembling the sedimentological makeup of the Ammer floodplain was generated and used to perform flow and transport simulations, using exposure of groundwater to TOC as proxy for reactivity. The study demonstrates that the spatial arrangement of facies and their combined biogeochemical and hydraulic properties determine over which range of times the breakthrough of nitrate is to be expected, highlighting the importance of sedimentological insights for groundwater-quality projections.

The project seeks to generate an overview of the water resources situation in the Palo Colorado community, Mexico. This community was chosen as the study site because it is located within a mining region with a high degree of marginalization, where further studies on water assessment and supply are necessary. The region was many abandoned mining projects, where the wastes and tailings were left exposed to weatherization. The abandoned sinkholes were later floded and used as water reservoirs for domestic and agricultural uses. Preliminary analyses show that the water from two of its main dams, “La Cruz Dam” and “Chica Dam”, is contaminated with potentially toxic elements (EPTs), such as Cr, Hg and Pb above the maximum permissible limits of the drinking water normativity. Furthermore, the presence of this heavy metals has been linked to health issues within the inhabitants of the community. The objective of the study is to diagnose and evaluate water quality, and the sustainable use of water resources, through hydrogeochemical studies to understand the mechanisms that govern the liberation, mobility and fate of the PTEs in order to develope a remediation strategy or water treatment solution.

Cells of magnetotactic bacteria (MTB) typically contain single crystals of magnetite that have strain-specific and distinct morphologies. Crystal habits deviate from the equilibrium form, the octahedron; categories including ‘cubooctahedral’, ‘prismatic’ and ‘bullet-shaped’ are widely used in the MTB literature [1]. These morphologies have been used as biomarkers, can affect the magnetic properties of the crystals and cells [2], and may offer insight into the genetic background of control over crystal growth. However, the exact morphologies of the magnetite nanocrystals have not been systematically determined.

We performed electron tomography (ET) by obtaining tilt series of high-angle annular dark-field (HAADF) images in a scanning transmission electron microscope (STEM), since the HAADF image contrast is not affected by diffraction and is directly proportional to specimen thickness. Magnetite shapes were characterized in various MTB strains containing octahedral, ‘prismatic’, ‘ladyfinger’- and ‘bullet-shaped’ particles. While the crystals of the first two types were bound by well-defined, indexable facets, the latter two types had irregular surfaces consisting of short segments of low-index faces. A common feature of all magnetite types was a pervasive presence of voids inside the nanocystals, suggesting a growth process dominated by particle attachment. ‘Non-classical’ crystal growth by the attachment and recrystallization of precursor nanoparticles is well known in several mineral systems; however, it is surprising that euhedral, single magnetite crystals form in this way. Provided that our interpretation of the growth process is correct, the current view of the genetic control over magnetite formation in MTB might need to be revised [3].

References

[1] Pósfai, M. et al., Phylogenetic significance of composition and crystal morphology of magnetosome minerals, Frontiers in Microbiology, 4 (2013) 67524.

[2] Kovács, A. et al., Influence of crystal shape and orientation on the magnetic microstructure of bullet-shaped magnetosomes synthesized by magnetotactic bacteria, Geo-Bio Interfyaces, 1 (2024) p.e1.

[3] We acknowledge support from the National Research, Development and Innovation Office (Hungary) under grant RRF-2.3.1-21-2022-00014.