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    Item type:Publication, Access status: with files ,
    Synthetic polymers promote cell aggregation and accelerate cathode-associated layer formation in Kyrpidia spormannii EA-1
    (Elsevier, 2026-09-15)
    Rominger, Leonie
    ;
    Deb, Amit
    ;
    Lapp, Christian Jonas
    ;
    Fernandez-Trillo, Francisco (Paco)
    ;
    Gescher, Johannes
    Microbial electrosynthesis using Kyrpidia spormannii EA-1 represents a promising approach for sustainable biotechnology, yet the initial biofilm formation on cathode surfaces remains a bottleneck limiting process efficiency. In this study, we investigated the potential of synthetic polymers to accelerate cell aggregation and cathode colonization by this microorganism in bioelectrochemical systems. Polymers were prepared through conjugation, in aqueous conditions, of a poly(hydrazide) (pAcU) with twelve different aldehydes including aromatic, heterocyclic, and aliphatic aldehydes. Crystal violet staining identified four promising polymer-aldehyde conjugates (with 2-naphthaldehyde, 1H-imidazole-4-carbaldehyde, uracil-5-carbaldehyde, and hexanal), one of which significantly increased crystal-violet-retained surface-attached biomass compared to its aldehyde-only control. Growth kinetics revealed that these polymer-aldehyde conjugates initially reduced apparent planktonic growth rates, which may reflect stress responses, reduced viability, or a shift toward an aggregated, surface-associated lifestyle. Live/dead staining demonstrated that cells became entrapped within aggregates, with viability depending on the specific aldehyde used. Transcriptomic analysis revealed upregulation of sporulation genes, toxin-antitoxin systems, and stress response pathways, alongside downregulation of metabolic transporters and carbon metabolism genes, a response compatible with, but not specific to, a biofilm-associated lifestyle. In a bioelectrochemical reactor, addition of the polymer-2-naphthaldehyde conjugate accelerated cathode coverage, with a cathode-associated layer reaching over 1 mm in height within seven days, compared to 0.17 mm in the biotic control and 0.24 mm in an abiotic polymer-only control, indicating a substantial contribution of both cellular aggregation and polymer deposition to layer formation. These findings indicate that synthetic polymer-aldehyde-conjugates represent a promising strategy to accelerate cathode colonization during the start-up phase of microbial electrosynthesis processes with K. spormannii.
    Publicationtype: Journal Article
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    Item type:Publication, Access status: with files ,
    Efficiency and process development for microbial biomass production using oxic bioelectrosynthesis
    (Elsevier, 2025-03)
    Rominger, Leonie
    ;
    Hackbarth, Max
    ;
    Jung, Tobias
    ;
    Scherzinger, Marvin
    ;
    Rosa, Luis F. M.
    Autotrophic microbial electrosynthesis (MES) processes are mainly based on organisms that rely on carbon dioxide (CO2) as an electron acceptor and typically have low biomass yields. However, there are few data on the process and efficiencies of oxic MES (OMES). In this study, we used the knallgas bacterium Kyrpidia spormannii to investigate biomass formation and energy efficiency of cathode-dependent growth. The study revealed that the process can be carried out with the same electron efficiency as conventional gas fermentation, but overcomes disadvantages, such as the use of explosive gas mixtures. When accounting only for the electron input via electrical energy, a solar energy demand of 67.89 kWh kg–1 dry biomass was determined. While anaerobic MES is ideally suited to produce methane, short-chain alcohols, and carboxylic acids, its aerobic counterpart could extend this important range of applications to not only protein for use in the food and feed sector, but also further complex products
    Publicationtype: Journal Article
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    Item type:Publication, Access status: with files ,
    Entwicklung eines Prozesses zur oxischen mikrobiellen Elektrosynthese mit Kyrpidia spormannii unter besonderer Berücksichtigung der Prozesseffizienz
    (2025)
    Rominger, Leonie
    ;
    Gescher, Johannes
    With the help of microbial electrosynthesis (MES), carbon dioxide from industrial point sources can be converted into chemical energy storages under biocatalysis, using electricity generated from renewable sources. Anoxic MES processes are already being used in industry, for example for the production of acetic acid or methane. However, the biomass yields are low and the range of products is limited. In contrast, oxic microbial electrosynthesis (oMES) enables the produc tion of more valuable products and biomass. However, biofilm-based oMES processes have so far been insufficiently characterised, particularly with regard to their energy efficiency. There is a lack of studies analysing efficiency across different stages of biofilm growth. The influence of oxygen concentration on microbial growth, but also on the efficiency of the process, is not yet sufficiently understood. In addition, there is a lack of methods for continuous biofilm harvesting and investigations into the use of industrial flue gas as a substrate. In this work, the oMES was operated with the Knallgas-bacterium Kyrpidia spormannii. The bioelectrochemical system used allowed non-invasive quantification of the biofilm using optical coherence tomography (OCT). This allowed to record growth kinetics, which determined the potential for the fastest biofilm growth at-375mV to-500mV vs SHE. Furthermore, the Coulombic efficiency could be determined over the process duration. It was 100% in the most efficient phase. At this point, no system-side electron losses occurred, meaning that oMES cultivation achieved the same efficiency as Knallgas fermentation, but without the disadvantage of handling explosive gas mixtures. By modelling biofilm growth, the oxygen demand for the current growth phase of the biofilm could be predicted, and electron losses resulting from oxygen reduction could be reduced. With 35,8kWh for the production of 1kg dry biomass, the energy requirement of the oMES process was also competitive with a two-stage Knallgas fermentation. A method was developed to harvest the biofilm via hydrogen bubbles. The biofilm was able to regenerate after being partially harvested. The harvested biomass had a protein content of around 62%. By adding a synthetic polymer, the initial growth phase of the biofilm until complete electrode coverage could be shortened. Finally, it was shown that the use of industrial flue gas as a substrate did not inhibit growth.
    Publicationtype: Doctoral Thesis
      88  40