Publications

Alga-dominated geothermal spring communities in Yellowstone National Park (YNP), USA, have been the focus of many studies, however, relatively little is known about the composition and community interactions which underpin these ecosystems. Our goal was to determine, in three neighboring yet distinct environments in Lemonade Creek, YNP, how cells cope with abiotic stressors over the diurnal cycle. All three environments are colonized by two photosynthetic lineages, Cyanidioschyzon and Galdieria, both of which are extremophilic Cyanidiophyceae red algae. Cyanidioschyzon, a highly specialized obligate photoautotroph, dominated cell counts at all three Lemonade Creek environments. The cell cycle of Cyanidioschyzon in YNP matched that observed in synchronized cultures, suggesting that light availability plays a strong role in constraining growth of this alga in its natural habitat. Surprisingly, the mixotrophic and physiologically more flexible Galdieria, was a minor component of these algal populations. Arsenic detoxification at Lemonade Creek occurred via complementary gene expression by different eukaryotic and prokaryotic lineages, consistent with this function being shared by the microbial community, rather than individual lineages completing the entire pathway. These results demonstrate the highly structured nature of these extreme habitats, particularly regarding arsenic detoxification.

Formate dehydrogenases catalyze the reversible oxidation of formate to carbon dioxide. These enzymes play an important role in CO2 reduction and serve as nicotinamide cofactor recycling enzymes. More recently, the CO2-reducing activity of formate dehydrogenases, especially metal-containing formate dehydrogenases, has been further explored for efficient atmospheric CO2 capture. In this sense, molecular hydrogen (H2) as the fuel of the future represents an efficient, cheap and environmentally friendly reducing agent when produced from renewable sources. Hydrogenases are enzymes that catalyze the reversible oxidation of H2. Herein, the functional interplay between the soluble [NiFe] hydrogenase from upriavidus necator and the molybdenum-dependent formate dehydrogenase from Rhodobacter capsulatus was investigated in a coupled biocatalytic system. H2-driven CO2 reduction (H2CO2R) using methyl viologen as an artificial electron mediator gave a higher product yield of formate than using NAD+ as the physiological electron mediator. The enzymes were stable under anaerobic conditions for 18 h, making the coupled reaction suitable for biotechnological purposes.

CO2 mineralization is a crucial carbon capture and utlization technique because it can sequester CO2 emissions permanently. There are various CO2 mineralization technological pathways, all of which are based on the reaction of CO2 with the metal oxides present in cementitious materials and virgin minerals. However, there are techno-economic obstacles that hinder their deployment, as well as various knowledge gaps regarding the prospective supply chains. Although these pathways have several differences, such as process configuration and costs, each is usually addressed individually and comparative analysis is lacking. In this contribution, we aim to address this knowledge gap via investigating the entire supply chain of each technology and contrasting their differences by presenting a case study from the German federal state of North Rhine-Westphalia. Methodologically, several approaches and tools are used, such as cost modeling and geographic information systems. Herein, we investigate the advantages and limitations by assessing six scenarios representing the different configurations of the relevant supply chains. Most scenarios are deemed infeasible at lower carbon prices, with only three considered viable below 100 €/ton CO2. Also, while concrete curing and concrete waste processes are constrained by material availability and logistics, CO2 mineralization of virgin minerals offers a more abundant alternative, albeit at a higher levelized cost. Therefore, the study provides valuable insights for the design of optimal and efficient CO2 mineralization supply chains, highlighting the need for a balanced approach that leverages the strengths of different pathways.

The pathogen Pseudomonas aeruginosa enhances its virulence and antibiotic resistance upon formation of durable biofilms. The exopolysaccharides Pel, Psl and alginate essentially contribute to the biofilm matrix, but their secretion mechanisms are barely understood. Here, we reveal the architecture of the outer membrane complex PelBC for Pel export, where the essential periplasmic ring of twelve lipoproteins PelC is mounted on top of the nanodisc-embedded β-barrel PelB. The PelC assembly is stabilized by electrostatic contacts with the periplasmic rim of PelB and via the membrane-anchored acyl chains. The negatively charged interior of the PelB β-barrel forms a route for the cationic Pel exopolysaccharide. The β-barrel is sealed at the extracellular side, but molecular dynamic simulations suggest that the short loop Plug-S is sufficiently flexible to open a tunnel for the exopolysaccharide transport. This gating model is corroborated by single-channel conductivity measurements, where a deletion of Plug-S renders a constitutively open β-barrel. Our structural and functional analysis offers a comprehensive view on this pathogenicity-relevant complex and suggests the route taken by the exopolysaccharide at the final secretion step.

Biomass is a finite yet increasingly demanded renewable energy resource, creating the need
to identify utilization pathways that deliver both financial returns and societal benefits. Existing
assessments often emphasize economic performance and global warming potential while
overlooking environmental externalities and inconsistently accounting for avoided and re-
moved CO₂-equivalent (CO₂eq) emissions. These gaps limit their ability to guide pathway-
level trade-off assessment and policy design.
This study presents a novel framework that integrates techno-economic analysis, life cycle
assessment, and monetization of environmental externalities to derive two central metrics: net
private benefit (NPB) and net social benefit (NSB). Expressing results per unit of biomass
input allows consistent comparison across heterogeneous pathways, such as heat, biochar,
and carbon removal credits. The framework distinguishes among types of emissions and re-
source use, incorporates multiple environmental impact categories, and links private and so-
cietal perspectives to support investment and policy decisions.
The framework’s application to miscanthus utilization in Germany compares bioenergy (BE)
and biochar carbon removal (BCR). BE yields positive NPB and avoids emissions and re-
source use but does not achieve permanent CO₂eq emission removal. BCR removes CO₂eq
emissions long-term but results in negative NPB. Both pathways, however, show positive NSB,
highlighting synergies and conflicts between private incentives and societal value.
Overall, this framework enables a holistic assessment of biomass utilization pathways. By
integrating economic and environmental dimensions, standardizing emissions and resource
use accounting, and harmonizing metrics, it provides a structured basis for evaluating trade-
offs across biomass utilization pathways regarding their private and social benefits.

The opportunistic pathogen Pseudomonas aeruginosa ensures its survival by forming mechanically and chemically resistant biofilms, with cationic exopolysaccharide Pel as an abundant constituent of the structural matrix. Despite its biomedical relevance, the mechanisms of Pel synthesis and secretion via the trans-envelope protein machinery are not understood. Here, we examine the structure of the outer membrane export complex PelBC embedded in synthetic nanodiscs and polymer-extracted particles. Both environments preserve the unique architecture of the complex, where the β-barrel PelB is capped with the dodecameric ring of PelC lipoproteins. Cryogenic electron microscopy shows that the polymer-extracted PelB β-barrel is tightly associated with phospholipids and lipid A molecules, and the membrane-facing PelC ring may stabilize lipids of the periplasmic leaflet in defined positions. All-atom molecular dynamics simulation of PelBC in the asymmetric outer membrane of P. aeruginosa corroborate the structural findings and visualize how the essential C-terminal helix of PelC forms multiple electrostatic contacts with the periplasmic leaflet of the outer membrane. Those interactions reduce the lateral mobility of the lipids, stabilize the position of the ring at the interface and may guide folding and assembly of the polysaccharide export machinery.

Extremophilic red microalgae are promising platforms for sustainable biotechnology, combining robust growth under selective thermoacidophilic conditions with production of thermostable phycobiliproteins and carbon-rich biomass. However, reactor-dependent effects on growth, product formation and biomass composition remain insufficiently resolved. Here, we systematically evaluated the extremophilic red microalga Cyanidioschyzon merolae across cultivation scales and reactor formats and benchmarked its performance against the well-established Galdieria javensis and Limnospira platensis. In small-scale multi-cultivator photobioreactors and microfluidic growth chambers, C. merolae showed superior growth, reaching a maximum growth rate of 0.034 ± 0.001 h^-1 and 8.3 ± 0.3 g l^-1 cell dry weight. Microfluidic cultivation enabled growth analysis at single-cell resolution and matched growth rates obtained in photobioreactors. To identify scalable production strategies, C. merolae was further cultivated in a flat-panel photobioreactor and a custom-designed internally illuminated photobioreactor. The custom-designed photobioreactor delivered the highest biomass concentration and productivity, yielding 11.5 ± 0.6 g l^-1 cell dry weight and 1.07 ± 0.06 g l^-1 d^-1, and comparable yields with regard to R-phycocyanin and R-allophycocyanin. Biomass analysis revealed substantial carbon and nitrogen contents, starch accumulation up to > 20 % of cell dry weight, and fatty acids dominated by palmitic, linoleic and oleic acids. Despite its reduced cell wall fraction, C. merolae contained structurally diverse, cultivation-dependent polysaccharides. These results establish C. merolae as a versatile chassis for thermostable pigment production and renewable feedstock generation, highlighting photobioreactor design as a key determinant of productivity and biomass quality.

This article examines the debate about what non-experts can assess when determining who
qualifies as an expert. We focus in particular on the debate about metacriteria for expertise
that non-experts can rely on. We make three central claims about what non-experts can
actually infer about experts: (1) metacriteria are not indicators of expertise; (2) instead,
they are indicators of experience and lack of epistemic integrity, with the latter marking
whether the preconditions for any meaningful assessment of expertise or experience are
even given; (3) by reframing the discussion about metacriteria of expertise in this way, we
situate the debate about the identification of experts within the broader debate on trust in
science. We argue that indicators of experience and lack of epistemic integrity are best
understood as indicators of epistemic trustworthiness. We also connect our analysis of
these indicators of epistemic trustworthiness to questions raised in the context of epistemic
trespassing. In particular, we argue that what distinguishes problematic epistemic tres-
passing from fruitful boundary crossing is that trespassing experts lack the required
experience (i.e., specialist tacit knowledge).