Biology subjects

Niedermeyer, T. H. J.

Publications and source records attributed to Niedermeyer, T. H. J..

3 recordsLinked to original sources

bioRxiv2026

Curation of mass spectrometry reference data for improved identification and dereplication of cyanobacterial specialized metabolites

High-resolution tandem mass spectrometry (HRMS/MS) is a powerful tool for screening organic compounds in complex samples. A critical step in identifying candidate structures is the comparison of sample HRMS/MS spectra with those in reference spectral libraries. The effectiveness of this spectral matching hinges on two key factors: (i) how well the librarys content aligns with the suspect compound list, and (ii) the quality and diversity of the reference spectra for each compound. Yet, the scarcity of natural product reference materials on the market often necessitates non-targeted analysis. In this study, we systematically acquired and curated HRMS/MS reference spectra for specialized metabolites from cyanobacteria, which are vastly underrepresented in current libraries. Previously, MassBank EU included spectra for only 14 such compounds. We have significantly expanded the publicly available data, contributing 2911 unique spectra representing 150 distinct cyanobacterial metabolites. A proof-of-concept analysis demonstrates up to 5-fold increased annotation success and revealed shortcomings in current libraries, underscoring the need for continued data enrichment. In particular, future efforts should prioritize the inclusion of HRMS/MS spectra for diverse adduct ions to improve identification confidence and broaden analytical coverage.

pharmacology and toxicology↗

bioRxiv2025

Aetokthonotoxin, the causative agent of vacuolar myelinopathy, uncouples oxidative phosphorylation due to protonophore activity

Aetokthonotoxin (AETX) is an emerging environmental toxin produced by the freshwater cyanobacterium Aetokthonos hydrillicola. Accumulating in the food chain, it causes vacuolar myelinopathy, a neurological disease affecting a wide range of wildlife characterized by the development of large intra-myelinic vacuoles in the white matter of the brain. So far, the mode of action of AETX is unknown. After discovering that AETX is cytostatic and arrests cancer cell lines in G1-phase, metabolomic profiling of AETX-treated cells as well as an assessment of the physico-chemical properties of the compound suggested that AETX is a weakly acidic uncoupler of mitochondrial respiration. We confirmed this hypothesis by in vitro assays on mammalian cells, finding that AETX has the expected effects on the mitochondrial network morphology, mitochondrial membrane potential, and oxygen consumption rates, resulting in affected ATP generation. We confirmed that AETX is capable of transporting protons across lipid bilayers. In summary, we demonstrate that AETX is a protonophore that uncouples oxidative phosphorylation in mitochondria, the primary event of AETX intoxication. Significance statementAetokthonotoxin (AETX) is an emerging cyanotoxin. Produced by the cyanobacterium Aetokthonos hydrillicola, it is transferred through the food chain, affects the nervous system, and eventually causes mortality in animals of various taxa. Our finding that AETX is an unspecific uncoupler of mitochondrial respiration implies that it might also be harmful for human health upon ingestion and trophic accumulation. First steps towards a full risk assessment are needed. An important aspect in this regard is the elucidation of the toxins mode of action. We anticipate our findings to be a starting point for the development of an adverse outcome pathway addressing the formation of vacuolar myelinopathy, expanding the significance of our results to the future risk assessment of other environmental neurotoxins.

pharmacology and toxicology↗

bioRxiv2023

More than just an Eagle Killer: The freshwater cyanobacterium Aetokthonos hydrillicola produces highly toxic dolastatin derivatives

Cyanobacteria are infamous producers of toxins. While the toxic potential of planktic cyanobacterial blooms is well documented, the ecosystem level effects of toxigenic benthic and epiphytic cyanobacteria are an understudied threat. The freshwater epiphytic cyanobacterium Aetokthonos hydrillicola has recently been shown to produce the "eagle killer" neurotoxin aetokthonotoxin causing the fatal neurological disease Vacuolar Myelinopathy. The disease affects a wide array of wildlife in the southeastern United States, most notably waterfowl and birds of prey, including the bald eagle. In an assay for cytotoxicity, we found the crude extract of the cyanobacterium to be much more potent than pure aetokthonotoxin, prompting further investigation. Here, we describe the isolation and structure elucidation of the aetokthonostatins, linear peptides belonging to the dolastatin compound family, featuring a unique modification of the C-terminal phenylalanine derived moiety. Using immunofluorescence microscopy and molecular modeling, we confirmed that aetokthonostatin acts as a potent tubulin binder. We also show that aetokthonostatin inhibits reproduction of the nematode C. elegans, resulting in increased population lethality of the combined action of the two toxins produced by A. hydrillicola. Bioinformatic analysis revealed the aetokthonostatin biosynthetic gene cluster encoding a non-ribosomal peptide synthe-tase/polyketide synthase accompanied by a unique tailoring machinery. The biosynthetic activity of a specific N-terminal methyltransferase was confirmed by in vitro biochemical studies, establishing a mechanistic link between the gene cluster and its product. Significance StatementCyanotoxins have adverse effects on ecosystems. Our understanding of their potential risk has recently been expanded by the discovery of aetokthonotoxin, produced by the cyanobacterium Aetokthonos hydrillicola growing on invasive plants. Via trophic transfer, it acts as a neurotoxin causing mortality in animals including top predators like Bald Eagles. Closer examination of A. hydrillicola revealed that it also produces highly toxic dolastatin derivatives. A. hydrillicola is the first cultured cyanobacterium producing dolastatin derivatives, allowing us to uncover biosynthetic gene clusters of this compound family. In contrast to all other known dolastatin-producers, which are marine cyanobacteria, A. hydrillicola thrives in freshwater reservoirs, making it a potential threat also for human health. Monitoring of the cyanobacterium and its toxins is strongly recommended.

microbiology↗