Biology subjects

Geelhoed, J. S.

Publications and source records attributed to Geelhoed, J. S..

4 recordsLinked to original sources

bioRxiv2026

Highly efficient bio-catalytic oxygen reduction coupled to long-range electron transport in cable bacteria

Multicellular cable bacteria are capable of transferring electrons over centimeter distances through an internal array of conductive fibers. These long, filamentous bacteria function as a living electrochemical cell, performing sulfide reduction at one end and oxygen reduction at the other end. To investigate how O2 reduction is linked to the long-distance electron transport along the conductive fibers, we performed a detailed electrochemical characterization of native filaments as well as extracted "fiber skeletons" without membranes or cytoplasm. Our data show that fibers skeletons only perform longitudinal electron transport and are not electrochemically active towards oxygen. This opposes a previous proposition that the conductive fiber network displays electrocatalytic behavior towards oxygen. Still, native cable bacterium filaments are capable of high oxygen reduction rates, thus demonstrating that dedicated enzyme systems in the periplasm or inner membrane are responsible for O2 reduction. Together, our data provide empirical support for a model in which diffusible c-type cytochromes mediate electron transport through the periplasm, shuttling electrons between separate respiratory complexes and the conductive fiber network. As such, our study resolves a crucial aspect of the unique electrogenic metabolism in cable bacteria, and clarifies the application potential of the highly conductive fibers in Bio-electrochemical System technologies.

microbiology↗

bioRxiv2025

A hierarchical nickel organic framework confers high conductivity over long distances in cable bacteria

Multi-cellular cable bacteria have evolved a unique machinery that efficiently transports electrons across centimetre-scale distances. Currents flow through a parallel network of periplasmic fibres, which display an extraordinary conductivity for a biological material. However, the conduction mechanism remains elusive as the molecular structure of the fibres has not been resolved. Here, we demonstrate that each fibre embeds a bundle of intertwined nanoribbons, which are built from Nickel Bis(Dithiolene) (NiBiD) repeat units that are formed by linking nickel centres with ethenetetrathiolate ligands. The planar and conjugated NiBiD complexes are aligned and stacked to form an elongated supramolecular coordination network, thus explaining the observed organo-metal electronic properties of the fibres. Our results hence demonstrate that biology is capable of producing extensive metal organic frameworks. These structures enable highly conductive one-dimensional conduits, ensuring efficient charge transport over macroscale distances, thus providing a novel design principle for bio-based, sustainable organo-electronic materials.

molecular biology↗

bioRxiv2020

Efficient long-range conduction in cable bacteria through nickel protein wires

Filamentous cable bacteria display unrivalled long-range electron transport, generating electrical currents over centimeter distances through a highly ordered network of fibers embedded in their cell envelope. The conductivity of these periplasmic wires is exceptionally high for a biological material, but their chemical structure and underlying electron transport mechanism remain unresolved. Here, we combine high-resolution microscopy, spectroscopy, and chemical imaging on individual cable bacterium filaments to demonstrate that the periplasmic wires consist of a conductive protein core surrounded by an insulating shell layer. The core proteins contain a sulfur-ligated nickel cofactor, and conductivity decreases when nickel is oxidized or selectively removed. The involvement of nickel as the active metal in biological conduction is remarkable, and suggests a hitherto unknown form of electron transport that enables efficient conduction in centimeter-long protein structures.

microbiology↗

bioRxiv2017

Transient exposure to oxygen or nitrate reveals ecophysiology of fermentative and sulfate-reducing benthic microbial populations

Conflict of interestThe authors declare no conflict of interest.\n\nShort summaryFermentation coupled to sulfate reduction is a globally important process for the remineralization of organic carbon in marine sediments. The present study uses long-term, replicated continuous culture bioreactors and meta-omics to investigate the ecophysiology of the involved microbial populations at an unprecedented resolution. We reveal complex trophic networks, in which fermenters and sulfate reducers coexist with nitrate- and oxygen respirers, we indicate strategies and niches of the microbial populations, and describe a novel and widespread, yet uncultured fermentative organism. These insights are crucial to understand fermentation coupled to sulfate reduction and relevant to assess microbial dynamics and community-level responses in coastal ecosystems.\n\nFor the anaerobic remineralization of organic matter in marine sediments, sulfate reduction coupled to fermentation plays a key role. Here, we enriched sulfate-reducing/fermentative communities from intertidal sediments under defined conditions in continuous culture. We transiently exposed the cultures to oxygen or nitrate twice daily and investigated the community response. Chemical measurements, provisional genomes and transcriptomic profiles revealed trophic networks of microbial populations. Sulfate reducers coexisted with facultative nitrate reducers or aerobes enabling the community to adjust to nitrate or oxygen pulses. Exposure to oxygen and nitrate impacted the community structure, but did not suppress fermentation or sulfate reduction as community functions, highlighting their stability under dynamic conditions. The most abundant sulfate reducer in all cultures, related to Desulfotignum balticum, appeared to have coupled acetate oxidation to sulfate reduction. We described a novel representative of the widespread uncultured phylum Candidatus Fermentibacteria (formerly candidate division Hyd24-12). For this strictly anaerobic, obligate fermentative bacterium, we propose the name Ca. \"Sabulitectum silens\" and identify it as a partner of sulfate reducers in marine sediments. Overall, we provide insights into the metabolic network of fermentative and sulfate-reducing microbial populations, their niches, and adaptations to a dynamic environment.

microbiology↗