Biology subjects

Sonntag, A.

Publications and source records attributed to Sonntag, A..

5 recordsLinked to original sources

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↗

bioRxiv2024

Bumblebees increase their learning flight altitude in dense environments

Bumblebees rely on visual memories acquired during the first outbound flights to relocate their nest. While these learning flights have been extensively studied in sparse environments with few objects, little is known about how bees adapt their flight in more dense, cluttered, settings that better mimic their natural habitats. Here we investigated how environmental complexity influences the first outbound flights of bumblebees. In a large arena we tracked the bees 3D positions to examine the flight patterns, body orientations, and nest fixations across environmental conditions characterised by different object constellations around the nest entrance. In cluttered environments, bees prioritised altitude gain over horizontal distance, suggesting a strategy to overcome obstacles and visual clutter. Body orientation patterns became more diverse in dense environments, indicating a balance between nest-oriented learning and obstacle avoidance. Notably, bees consistently preferred to fixate the location of the nest entrance from elevated positions above the dense environment across all conditions. Our results reveal significant changes in the 3D flight structure, body orientations, and nest fixation behaviours as object density increases. This highlights the importance of considering 3D space and environmental complexity in understanding insect navigation.

animal behavior and cognition↗

bioRxiv2024

Bumblebees locate goals in 3D with absolute height estimation from ventral optic flow

When foraging, flying animals like bees are often required to change their flight altitude from close to the ground to above the height of the vegetation to reach their nest or a food source. While the mechanisms of navigating towards a goal in two dimensions are well investigated, the explicit use of height as a source for navigation in three dimensions remains mostly unknown. Our study aims to unravel which strategies bumble-bees use for height estimation and whether they rely on global or local cues. We expanded a 2D goal localization paradigm, where a goal location is indicated by cylindrical landmarks, to the third dimension by using spherical landmarks to indicate a feeders position in 3D and examined the search pattern of bumblebees. Additionally, we assessed the ability of bees to estimate the height of a feeder based on local landmarks and global references such as the ground floor. The search distribution for a feeders position in 3D was less spatially concentrated compared to in 2D. Assessing the bees height estimation ability, we found that bees could estimate a feeders height using the ground floor as a reference. However, the feeder needed to be sufficiently close to the ground floor for the bees to choose correctly. When bumblebees are faced with the challenge of foraging in a 3D environment where the height of a food source and landmark cues are important, they demonstrate the ability to learn and return to a specific flower height. This suggests they rely on ventral optic flow for goal height estimation in bumblebees.

animal behavior and cognition↗

bioRxiv2023

Switching perspective: Comparing ground-level and bird's-eye views for bees navigating clutter

Animals navigating in three dimensions encounter different perspectives of their world, often transitioning from birds eye views at higher altitudes to ground views closer to the ground. How they integrate this information to pinpoint a goal location is virtually unknown. Here we tested the ability of bumblebees to use both types of views when homing in a dense environment in the vicinity of their inconspicuous nest entrance. Our combined modelling and experimental approach examined various views for localising a goal in dense settings. Whereas, birds-eye views performed best in simulations of current nest-centered snapshot homing models, behavioural experiments revealed that bumblebees predominantly relied on ground views when pinpointing nest entrances in dense environments. These findings reveal the limitations of snapshot-homing models and suggest that bumblebees use a combination of navigational tools to successfully find their way home in dense environments. This is not only relevant for understanding bee navigation, but also for other animals and humans navigating in 3D as well as the development of technologies inspired by natural systems, such as autonomous flying robots.

animal behavior and cognition↗

bioRxiv2019

Changes in lipid composition and ultrastructure associated with functional maturation of the cuticle during adult maize leaf development

Although extensive prior work has characterized cuticle composition, function, ultrastructure and development in many plant species, much remains to be learned about how these features are interrelated. Moreover, very little is known about the adult maize leaf cuticle in spite of its significance for agronomically important traits in this major crop. We analyzed cuticle composition, ultrastructure, and permeability along the developmental gradient of partially expanded adult maize leaves to probe the relationships between these features. The water barrier property is acquired at the cessation of cell expansion. Wax types and chain lengths accumulate asynchronously along the developmental gradient, while overall wax load does not vary. Cutin begins to accumulate prior to establishment of the water barrier and continues thereafter. Ultrastructurally, pavement cell cuticles consist of an epicuticular layer, a thin cuticle proper that acquires an inner, osmiophilic layer during development, and no cuticular layer. Cuticular waxes of the adult maize leaf are dominated by alkanes and wax esters localized mainly in the epicuticular layer. Establishment of the water barrier coincides with a switch from alkanes to esters as the major wax type, and the emergence of an osmiophilic (likely cutin-rich) layer of the cuticle proper.\n\nHiglight statementChemical, ultrastructural and functional analysis of cuticle development in partially expanded adult maize leaves revealed important roles for wax esters and an osmiophilic, likely cutin-rich, layer in protection from dehydration.

plant biology↗