Karina Krarup Sand

Summary: Iceland was among the last large islands settled by humans, with colonization (Landnám) in the late 9th century CE (Common Era) and is often portrayed as an ecological disaster driven by the Norse settlers. Here, we revisit this narrative through environmental DNA (eDNA) and multiproxy analyses of sediment cores from Lake Tjörnin in central Reykjavík, one of Iceland’s earliest and longest-occupied settlements. Originally a marine embayment, Tjörnin became a freshwater lake around 660 CE. Our record reveals a human presence decades before the long-accepted arrival date of 877 CE, marked by the Landnám volcanic tephra. Early settlement brought livestock, barley cultivation, and other introduced taxa that enhanced nutrient cycling and unexpectedly increased local biodiversity. Contrary to the conventional view of rapid deforestation, eDNA shows that birch and willow expanded during the settlement period, likely supported by deliberate management. Pronounced ecological and land use shifts occurred after 1200 CE, but these were coeval with the Little Ice Age cooling, compounded by volcanic eruptions, storm surges, and plague, rather than anthropogenic degradation. Crop cultivation ceased, arboreal taxa retracted, and grazing pressure maintained open landscapes. Even more profound ecological changes came after c. 1750 CE with urbanization and industrialization, as wastewater discharge, heavy-metal pollution, and fossil fuel use reshaped Tjörnin’s ecosystem. These findings challenge the prevailing model of Norse-induced environmental collapse, revealing instead a dynamic human–environment relationship shaped by both cultural practices and external stressors. By applying eDNA to a long-occupied urban catchment, we demonstrate the power of genomic methods to refine settlement chronologies, reassess ecological baselines and changes, and integrate natural and cultural histories. This approach offers a model for revisiting human–environment interactions in urban centers worldwide.

Horizontal gene transfer is one of the most important drivers of bacterial evolution. Transformation by uptake of extracellular DNA is traditionally not considered to be an effective mode of gene acquisition, simply because extracellular DNA is degraded in a matter of days when it is suspended in e.g. seawater. Recently the age span of stored DNA was increased to at least 2 Ma. Here, we show that Acinetobacter baylyi can incorporate 60 bp DNA fragments adsorbed to common sedimentary minerals and that the transformation frequencies scale with mineral surface properties. Our work highlights that ancient environmental DNA can fuel the evolution of contemporary bacteria. In contrast to heritable stochastic mutations, the processes by which bacteria acquire new genomic material during times of increased stress and needs, indicate a non-random mechanism that may propel evolution in a non-stochastic manner.

Mineral-polymer composites found in nature exhibit exceptional structural properties essential to their function, and transferring these attributes to the synthetic design of functional materials holds promise across various sectors. Biomimetic fabrication of nanocomposites introduces new pathways for advanced material design and explores biomineralization strategies. This study presents a novel approach for producing single platelet nanocomposites composed of CaCO₃ and biomimetic peptoid (N-substituted glycines) polymers, akin to the bricks found in the brick-and-mortar structure of nacre, the inner layer of certain mollusc shells. The significant aspect of the proposed strategy is the use of organic peptoid nanosheets as the scaffolds for brick formation, along with their controlled mineralization in solution. Here, we employ the B28 peptoid nanosheet as a scaffold, which readily forms free-floating zwitterionic bilayers in aqueous solution. The peptoid nanosheets were mineralized under consistent initial conditions (σ_calcite = 1.2, pH 9.00), with variations in mixing conditions and supersaturation profiles over time aimed at controlling the final product. Nanosheets were mineralized in both feedback control experiments, where supersaturation was continuously replenished by titrant addition and in batch experiments without a feedback loop. Complete coverage of the nanosheet surface by amorphous calcium carbonate was achieved under specific conditions with feedback control mineralization, whereas vaterite was the primary CaCO₃ phase observed after batch experiments. Thermodynamic calculations suggest that time-dependent supersaturation profiles as well as the spatial distribution of supersaturation are effective controls for tuning the mineralization extent and product. We anticipate that the control strategies outlined in this work can serve as a foundation for the advanced and scalable fabrication of nanocomposites as building blocks for nacre-mimetic and functional materials.

Retrieval of modern and ancient environmental DNA (eDNA) from sediments has revolutionized our ability to study past and present ecosystems. Little emphasis has been placed, however, on the fundamentals of the DNA–sediment associations in environmental settings. Consequently, our understanding of mineralogic controls and geochemical processes that take place on the DNA–sediment interface, and its implications for eDNA taphonomy and provenance, remain extremely limited. Here, we apply interfacial geochemical principles to elucidate how depositional processes and the stability of DNA–sediment associations in different environments can influence our interpretation and identify possible interpretational biases arising from neglecting mineral and geochemical controls on eDNA taphonomy. We use atomic force microscopy to show how interfacial geochemical interactions drive DNA adsorption behavior and we outline how to increase the scope and resolution of ecological interpretations from eDNA by combining mineralogic composition information with experimental adsorption data. We bring the concepts together and propose how to integrate sediment provenance as well as mineralogic and geochemical principles in eDNA taphonomy analysis for improved reconstruction of past ecosystems and monitoring of modern ecosystems from eDNA data. We provide a conceptual understanding of how eDNA taphonomy and sediment provenance can be addressed and further applied to enhance the scope, resolution, and accuracy of modern and past ecological reconstructions based on eDNA data.

The role of mineral surfaces in environmental processes, particularly their influence on DNA preservation, biofilm formation, and genetic transfer, has garnered attention due to its implications for the spread of antibiotic resistance genes (ARg). Despite the recognized significance of mineral-mediated DNA transfer, this mechanism remains poorly understood. Here we investigate the intricate interplay between soil minerals, bacteria, and DNA, to better understand the mechanisms driving ARg propagation in natural environments. We here study the uptake of mineral adsorbed DNA into the natural competent bacteria b. subtilis and further explore the influence of minerals on the viability and subsequent biofilm formation of both b. subtilis and A. baylyi. We further adsorbed DNA to mineral surfaces and allowed biofilm formation while monitoring the propagation of the ARg through out the biofilms. All the results are set in context of mineral surface properties such as surface charge, charge densities and surface area. Our results showed that the surface properties of the mineral surfaces are highly influencing the transformation efficiencies, viability and biofilm formation where in particular a high number of positive charged surface sites enhance biofilm formation and viability and inhibit transformation. The influence of the mineral surfaces diminishes as the biofilm develops and propagation of mineral adsorbed ARg are seen widely across the mineral surfaces. Our results have implication for mitigations strategies and reconcile mineral surfaces as hot spots for the propagation of antibiotic resistance-which indeed can be driven by transformation in the absence of bacteria carrying the traits. In principle all it takes is one successful transfer event from a mineral adsorbed ARg.

The extraction of environmental DNA (eDNA) from sediments is providing ground‐breaking views of past ecosystems and biodiversity. Despite this rich source of information, it is still unclear which sediments favor preservation and why. Here, we used atomic force microscopy and molecular dynamics simulations to explore the DNA‐mineral interaction to assess how mineralogy and interfacial geochemistry play a role in the preservation of environmental DNA on mineral substrates. We demonstrate that mineral composition, surface topography, and surface charge influence DNA adsorption behavior as well as preservation. Modeling and experimental data show that DNA damage can be induced by mineral binding if there is a strong driving force for adsorption. The study shows that knowledge of the mineralogical composition of a sediment and the environmental conditions can be useful for assessing if a deposit is capable of storing extracellular DNA and to what extent the DNA would be preserved. Our data adds to the understanding of eDNA taphonomy and highlights that, for some mineral systems, fragmented DNA may not represent old DNA.

Summary: Environmental DNA (eDNA) from the 2-million-year-old Kap København Formation of northern Greenland has revealed an ecosystem of plants and animals with no contemporary analogue ¹ . Here, we reconstruct the microbial (bacterial, archaeal, and viral) communities that thrived at the site during this time. By leveraging a novel analytical framework that integrates taxonomic profiling, DNA damage estimates, and functional reconstructions, we identify and distinguish pioneer microbial communities from later permafrost microbial assemblages. We show that at the time of sediment deposition, the terrestrial input at the Kap København site originated from a palustrine wetland, suggesting warmer, non-permafrost conditions. During this period, the detection of methanogenic archaea and signals of their carbon metabolism is consistent with Kap København and similar northern ecosystems contributing moderate methane emissions. Intriguingly, we discover a remarkable nucleotide sequence similarity—exceeding 98%—between pioneer methanogens and present-day analogues in thawing permafrost. This aligns with the concept of “time-traveling” microbes ² surviving across geological time and waiting for conditions to turn favourable rather than evolving to adapt to changing conditions. Importantly, in contrast to the plant and animal communities of the Kap København, a striking similarity in microbial composition to that of a contemporary thawing Arctic suggests that microbial communities may serve as the first indication of broader climate-driven ecosystem disruptions.