Biology subjects

Wissink, M.

Publications and source records attributed to Wissink, M..

5 recordsLinked to original sources

bioRxiv2026

Adaptation of the freshwater anaerobic methanotroph 'Ca. Methanoperedens vercellensis' to low pH levels reveals membrane lipid remodelling

Anaerobic methanotrophic archaea are key members of the biological methane filter, thereby preventing emissions of this strong greenhouse gas into the atmosphere. Previous studies on freshwater anaerobic methanotrophs targeted the activity of these microorganisms at circumneutral pH whereas molecular ecology studies identified this phylotype also in acidic environments such as peatlands; it is currently unknown whether they can adapt to low pH and remain effective in the biological methane filter in low pH environments. Here we show that a granular enrichment culture of the freshwater methanotroph Ca. M. vercellensis loses activity when experiencing pH stress but remains metabolically active down to pH 5.65 with appropriate adaptation time, indicating that adaptive changes are necessary to accommodate anaerobic methane oxidation at lower pH. Analyses of archaeal lipids revealed an increase in zwitterionic intact polar lipids over anionic lipids as an adaptation. This coincided with a change in granule structure while methane oxidation rate and enrichment state of Ca. M. vercellensis remained stable. We show that Ca. M. vercellensis remains metabolically active at lower pH values, despite increased maintenance energy demands and the need for cytoplasmic pH homeostasis. Our study demonstrates that adaptations to stress by slow-growing microorganisms may require long-term observation and is thereby instrumental for a better understanding of methane cycling in acidic ecosystems.

microbiology↗

bioRxiv2025

Mini-bacterioferritins: Structural insight into a new type of ferritin-like protein from an anaerobic methane-oxidising archaeon

Ferritins are ubiquitous among life forms, as they are essential for iron homeostasis. Here, we unveiled a novel member of the ferritin family, baptised mini-bacterioferritin. The characterised mini-bacterioferritin was isolated from a microbial enrichment dominated by the methanotrophic archaeon Candidatus Methanoperedens BLZ2. Its atomic resolution crystal structure reveals a 12-mer assembly with a diiron ferroxidase centre located within a four-helix bundle. Redox cycling experiments on protein crystals reveal a shift in iron position at the active site, which follows the established ferritin catalytic cycle. The 12-mer sphere-like structure harboured six Fe-coproporphyrin III ligands, positioned at the interdimeric interface, a characteristic previously only found in 24-mer bacterioferritins. Phylogenetics, together with structure predictions of closely related proteins, revealed that mini-bacterioferritins form a new clade within the ferritin family that might conserve ancestral traits. Future research will need to investigate the physiological roles of these enzymes, which were unsuspectingly widely distributed among prokaryotes. TeaserA novel ferritin family, the heme-binding mini-bacterioferritin, assembles as a dodecamer and is widely distributed among microbes.

biochemistry↗

bioRxiv2025

Atomic resolution structures of key enzyme MCR in anaerobic methanotrophy reveal novel and extensive post-translational modifications.

Anaerobic methanotrophic archaea (ANME) are crucial to planetary carbon cycling. They oxidise methane in anoxic niches by transferring electrons directly to nitrate or metal oxides and alternatively to sulfate-reducing bacteria. Due to their physiological complexity, no ANME species have been isolated, hampering the biochemical investigation of the enzymatic processes involved in anaerobic methane oxidation. To study the methane-capturing enzyme of these microorganisms, we circumvented the isolation barrier by exploiting microbial enrichments of freshwater nitrate-reducing ANME-2d grown in bioreactors, and marine ANME-2c in syntrophy with bacterial partners. The crystal structures of their Methyl-Coenzyme M Reductases (MCRs), refined to true atomic resolution, provided the most precise image of the enzyme to date. Despite their physiological differences, these ANMEs have extremely conserved MCR structures, similar to homologs from methanogenic Methanosarcinales, rather than the phylogenetically distant MCR of ANME-1 isolated from Black Sea mats. The three studied MCRs are highly modified, with seven post-translational modifications. Among them was a novel 3(S)-methylhistidine on the {gamma}-chain of both ANME-2d MCRs. Labelling with gaseous krypton did not reveal any internal channels that would facilitate alkane diffusion to the active site as observed in the ethane-specialized enzyme. Based on our data, the methanotrophic MCRs should follow the same radical reaction mechanism proposed for the methane-generating homologues. The described pattern of post-translational modifications underscores the importance of native purification as a powerful approach to discovering intrinsic enzymatic features in uncultivated microorganisms existing in nature.

microbiology↗

bioRxiv2023

Mechanisms of extracellular electron transfer in anaerobic methanotrophic archaea

Anaerobic methanotrophic (ANME) archaea are environmentally important uncultivated microorganisms mitigating the release of the potent greenhouse gas methane. During methane oxidation ANME archaea engage in extracellular electron transfer (EET) with other microorganisms, metal oxides, and electrodes, through a currently unknown mechanism. To shed light on this mechanism, we cultivated ANME-2d archaea (Ca. Methanoperedens) in bioelectrochemical systems and observed strong methane-dependent current (91-93% of total current) associated with high enrichment of Ca. Methanoperedens on the anode (up to 82% of the community) determined by metagenomics and transmission electron microscopy. Electrochemistry and metatranscriptomics indicated that the EET mechanism was similar at various electrode potentials pointing to the involvement of an so far uncharacterized short-range electron transport protein complex and OmcZ nanowires, suggesting a unique EET pathway in all ANME-2 archaea. Our findings furthermore indicate that bioelectrochemical cells might be powerful tools for the cultivation, and possibly isolation, of uncultured electroactive microorganisms.

microbiology↗

bioRxiv2021

Appetitive learning relies on octopamine and dopamine in ants

Associative learning relies on the detection of coincidence between a stimulus and a reward or punishment. In the insect brain, this process is thought to be carried out in the mushroom bodies under control of octopaminergic and dopaminergic neurons. It was assumed that appetitive learning is governed by octopaminergic neurons, while dopamine is required for aversive learning. This view has been recently challenged: Both neurotransmitters seem to be involved in both types of memory in bees and flies. Here, we test which neurotransmitters are required for appetitive learning in ants. We trained Lasius niger ant workers to discriminate two mixtures of linear hydrocarbons and associate one of them with a sucrose reward. We analysed the behaviour of the trained ants using machine learning and found that they preferred the rewarded odour over the other, a preference that was stable for at least 24 hours. We then treated the ants before learning with either epinastine, an octopamine receptor blocker, or with flupentixol, a dopamine receptor blocker. Ants with blocked octopamine receptors did not remember the rewarded odour. Octopamine signalling is thus necessary for the formation of appetitive memory. In contrast, ants with blocked dopamine receptors initially learned the rewarded odour but failed to retrieve this memory 24 hours later. Dopamine is thus required for long-term memory consolidation during appetitive conditioning, independent of short-term memory formation. Our results show that appetitive learning depends on both octopamine and dopamine signalling in ants.

animal behavior and cognition↗