Biology subjects

Kruse, S.

Publications and source records attributed to Kruse, S..

7 recordsLinked to original sources

bioRxiv2025

Human dimension of Holocene wildfire dynamics in boreal eastern Siberia

Severe wildfire seasons in the Republic of Sakha (Yakutia) raise questions regarding long-term fire dynamics and their drivers. However, data on long-term fire history remains scarce across eastern Siberia. We present the first composite of reconstructed wildfire dynamics in Yakutia throughout the Holocene, based on eight newly contributed records of macroscopic charcoal in lake sediments in combination with published data. Increased biomass burning occurred in the Early Holocene, c. 10,000 years BP, before shifting to lower levels at c. 6000 years BP. Independent simulations of climate-driven burned area in an individual-based forest model reproduce this reconstructed Holocene trend (rs = 0.85), but the correlation on centennial timescales turns negative in the Late Holocene (rs = -0.70). This mismatch suggests that climate alone cannot explain Late Holocene wildfire dynamics. We propose that a human dimension needs to be considered. By example of the settlement of the pastoralist Sakha people c. 800 years BP, we show that implementing reduced fuel availability from Indigenous land management in the forest model leads to improved centennial-scale correlations (rs = 0.96). This study highlights the need for a better understanding of the poorly reported human dimension of past fire dynamics in eastern Siberia.

ecology↗

bioRxiv2023

Tibetan terrestrial and aquatic ecosystems collapsed with cryosphere loss inferred from sedimentary ancient metagenomics

Glacier and permafrost shrinkage and land-use intensification threaten diverse mountain wildlife and affect nature conservation strategy. Our understanding of alpine ecological dynamics is, however, insufficient because time series portraying ecosystem complexity adequately are missing. Here, we present an ancient metagenomic record tracing 317 terrestrial and aquatic taxa, including mammals, fish, plants, and microorganisms retrieved from a lake sediment core from the southeastern Tibetan Plateau covering the last 18,000 years. We infer that steppe-meadow turned into woodland at 14 ka (cal BP) controlled by warming-induced cryosphere loss, further driving a change of herbivore dominance from wild yak to deer. Network analyses reveal that root hemiparasitic and cushion plants are keystone taxa, likely altering the terrestrial ecosystem via facilitation. These findings refute the hypothesis of top-down control by large herbivores in the alpine ecosystem. We also find that glacier mass loss significantly contributes to considerable turnover in the aquatic community at 14 ka, transitioning from glacier-related (blue-green) algae to abundant non-glacier-preferring picocyanobacteria, macrophytes, fish, and fish-eating otters. Human impact contributes little to shaping the alpine ecosystems. By applying network analysis, we provide the first sedaDNA-based assessment of the stress-gradient hypothesis. As cryosphere loss is ongoing due to climate warming, prioritizing the protection of habitats with rich nurse plants that aid neighbors in adapting to stressful conditions is likely to be a more beneficial conservation measure than livestock reduction in the Tibetan Plateau. Significance statementMerging ancient metagenomics and network analysis gives new insights into conserving the Tibetan alpine ecosystem under ongoing warming and human perturbations. We investigated the assembly of the Yak steppe-meadow ecosystem and an alpine lake system in response to cryosphere changes over the past [~]18,000 years on the Tibetan Plateau. Large herbivores cannot be a cost-effective natural climate solution to stabilize the Tibetan alpine ecosystem because they are not keystone taxa at the ecosystem scale. Furthermore, there is no support that land use considerably shapes the alpine communities and ecosystems. Protection policy should thus prioritize focus on alpine areas with intense land use and rich in root hemiparasitic and cushion plants because these taxa act as facilitators in the ecosystem.

ecology↗

bioRxiv2023

Stress response of fire salamander larvae differs between habitat types

Different habitats can impose varying selection pressures on individuals of the same species. Larvae of the European fire salamander (Salamandra salamandra) can inhabit two different habitats: streams and ponds. Streams are characterised by lower predation risk and intraspecific density and higher food availability than ponds. Thus, ponds are considered a less suitable habitat. To investigate the differential impacts of the two habitats on larval physiology, we measured the stress response of larvae living in the two different habitats. After successfully validating the measure of water-borne corticosterone (CORT) concentrations in fire salamander larvae, we measured the baseline and stress-induced CORT of 64 larvae from two pond and two stream locations in the field. We found larvae in ponds to be more stressed than larvae in streams. Additionally, we performed a reciprocal transplant experiment and tested whether larvae can adapt their stress response to changing habitat conditions. After two weeks of transfer, we did not find an increase in CORT when comparing stress-induced CORT values with baseline CORT values in larvae transferred into ponds. However, larvae transferred into streams exhibited an increase in the stress-induced CORT response. Moreover, transfer into ponds as well as larvae originating from ponds showed reduced growth rates, indicating that ponds might be the more stressful habitat, as it negatively affected larval physiology. These results show that noninvasive hormone measurements can provide information on habitat quality and potential adaptation and thus emphasis the potential for its use in conservation efforts.

ecology↗

bioRxiv2022

An Epitope-Focused Trypanosome-Derived Vaccine Platform Elicits High-Affinity Antibodies and Immunity Against Fentanyl Effects

Poorly antigenic small molecules pose challenges for the production of clinically efficacious antibodies. To address this, we have developed an immunization platform derived from the antigenic surface coat of the African trypanosome. Through sortase-based conjugation of antigens to the trypanosome surface coat protein variant surface glycoprotein (VSG), we created the VAST (VSG-immunogen Array by Sortase Tagging). We used VAST to elicit protective immunity to the effects fentanyl. Immunizing mice with fentanyl-VAST generated serological memory and protection from fentanyl challenge. Employing single-cell RNAseq, we then developed a streamlined method that synergizes with the VAST to identify immunization-elicited memory B cells and the antibodies they encode. All antibodies selected by this method displayed picomolar affinities for fentanyl. Passive immunization protected animals from fentanyl, while crystallography revealed that the mAbs bind fentanyl in an unusually deep pocket suited to small molecules, demonstrating the ability of the VAST to elicit high-quality therapeutic antibodies.

immunology↗

bioRxiv2021

Regional opportunities for Siberian tundra conservation in the next 1000 years

The biodiversity of tundra areas in northern high latitudes is threatened by invasion of forests under global warming. However, poorly understood nonlinear responses of the treeline ecotone mean the timing and extent of tundra losses are unclear but policymakers need such information to optimize conservation efforts. Our individual based model LAVESI, developed for the Siberian tundra-taiga ecotone, can help improve our understanding. Consequently, we simulated treeline migration trajectories until the end of the millennium, causing a loss of tundra area when advancing north. Our simulations reveal that the treeline follows climate warming with a severe, century-long time lag, which is overcompensated by infilling of stands in the long run even when temperatures cool again. Our simulations reveal that only under ambitious mitigation strategies (RCP 2.6) will ~30% of original tundra areas remain in the north but separated into two disjunct refugia.

ecology↗

bioRxiv2019

Interspecies metabolite transfer in a co-culture of Dehalococcoides and Sulfurospirillum leads to rapid and complete tetrachloroethene dechlorination

Microbial communities involving dehalogenating bacteria assist in bioremediation of areas contaminated with halocarbons. To understand molecular interactions between dehalogenating bacteria, we co-cultured Sulfurospirillum multivorans, dechlorinating tetrachloroethene (PCE) to cis-1,2-dichloroethene (cDCE), and Dehalococcoides mccartyi strains BTF08 or 195, dehalogenating PCE to ethene. The co-cultures were cultivated with lactate as electron donor. In this co-culture, the bacterial cells formed aggregates and D. mccartyi established an unusual, barrel-like morphology. An extracellular matrix surrounding bacterial cells in the aggregates enhanced cell-to-cell contact. PCE was dehalogenated to ethene at least three times faster in the co-culture. The dehalogenation was carried out via PceA of S. multivorans, and PteA (a recently described PCE dehalogenase) and VcrA of D. mccartyi BTF08, as supported by protein abundance. The co-culture was not dependent on exogenous hydrogen and acetate, suggesting a syntrophic relationship in which the obligate hydrogen consumer D. mccartyi consumes hydrogen and acetate produced by S. multivorans. The cobamide cofactor of the reductive dehalogenase - mandatory for D. mccartyi - was also produced by S. multivorans. D. mccartyi strain 195 dechlorinated cDCE in the presence of norpseudo-B12 produced by S. multivorans, but D. mccartyi strain BTF08 depended on an exogenous lower cobamide ligand. This observation is important for bioremediation, since cofactor supply in the environment might be a limiting factor for PCE dehalogenation to ethene, described for D. mccartyi exclusively. The findings from this co-culture give new insights into aggregate formation and the physiology of D. mccartyi within a bacterial community.

microbiology↗

bioRxiv2017

Hydrogen production by Sulfurospirillum spp. enables syntrophic interactions of Epsilonproteobacteria

Hydrogen-producing bacteria are of environmental and biotechnological importance in anoxic environments, since hydrogen is an important electron donor for prokaryotes and of interest as an alternative energy source. Epsilonproteobacteria, inhabiting ecologically, clinically or biotechnologically relevant environments, are currently considered to be hydrogen-oxidizing bacteria exclusively. Here, we report hydrogen production for a genus of free-living Epsilonproteobacteria, Sulfurospirillum spp. inhabiting sediments, wastewater plants, bioelectrodes, oil reservoirs, contaminated areas, or marine habitats. The amount of hydrogen production was largely different in two subgroups of Sulfurospirillum spp., represented by S. cavolei and S. multivorans. The former is shown to be the more potent hydrogen producer and excretes acetate as sole organic acid, while the latter exhibited a more flexible fermentation, producing additionally lactate and succinate. The observed hydrogen production could be assigned to a group 4 hydrogenase similar to Hydrogenase 4 (Hyf) in E. coli. We propose that Sulfurospirillum spp. produce molecular hydrogen with electrons derived from pyruvate oxidation by pyruvate:ferredoxin oxidoreductase and reduced ferredoxin. This hypothesis is supported by comparative proteome data, in which both PFOR and ferredoxin as well as hydrogenase 4 are up-regulated. A co-culture experiment with S. multivorans and Methanococcus voltae cultivated with lactate as sole substrate shows a syntrophic interaction between both organisms, since the former cannot grow fermentatively on lactate alone and the latter relies on hydrogen as electron donor. This opens up new perspectives on microbial communities, since Epsilonproteobacteria could play a yet unrecognized role as hydrogen producers in anoxic microbial communities.

microbiology↗