Biology subjects

Digel, L.

Publications and source records attributed to Digel, L..

4 recordsLinked to original sources

bioRxiv2025

Extracellular electron transfer in cable bacteria enables growth rates comparable to aerobic respiration

Cable bacteria are filamentous sulphide-oxidisers performing long-distance electron transfer in redox-stratified sediments by transporting electrons over centimetre-scale distances to reduce oxygen. Here, we show that the freshwater cable bacterium Electronema aureum GS can respire insoluble electron acceptors under anoxic conditions via a versatile extracellular electron transfer (EET) system, supporting growth rates comparable to those under aerobic conditions. Using electrochemical and molecular biology analyses, we demonstrate that E. aureum GS engages in both direct and mediated electron transfer to electrodes, including at +600 mV vs. Ag/AgCl--an unusually high redox potential typically not accessed by electroactive bacteria. Two distinct cell-surface redox components were identified, which are metal-dependent, pH-sensitive, and heat-labile, consistent with outer-membrane-localised cytochromes. Moreover, the redox shuttle riboflavin accumulated extracellularly and enhanced current production in bioelectrochemical systems, indicating a role for soluble mediators in cable bacteria. Together, these findings reveal a previously unrecognised respiratory flexibility in E. aureum GS and highlight EET as a key alternative strategy for energy conservation in fluctuating redox environments.

microbiology↗

bioRxiv2025

The 3D architecture of the ctenophore aboral organ and the evolution of complex integrative centers in animals

The ability to sense and respond to environmental cues is fundamental to animal behavior and survival. In ctenophores - early-branching marine animals - a syncytial nerve net underlies complex behaviors such as geotaxis, feeding, and escape. At the center of this system is the aboral organ (AO), a dense sensory hub that detects motion, light, and pressure and coordinates ciliary movement. However, the AOs cellular architecture and its integration with the nerve net remain poorly understood. Here, using volume electron microscopy in Mnemiopsis leidyi, we reveal that the syncytial nerve net converges and condenses around the AO, forming synaptic connections with diverse effector cells. We annotated 17 distinct cell types, including candidate light and pressure sensors, novel ciliated and secretory cells, and non-synaptic vesicle-rich cells likely involved in volume transmission. Our data shows that signal processing within the AO relies on both synaptic and non-synaptic communication. Gene expression profiling of conserved transcription factors indicates that the AO is a functionally convergent, evolutionarily distinct sensory structure that retains minimal homology. Our findings redefine the ctenophore AO as a highly integrated, multilayered sensory system critical for behavioral regulation.

evolutionary biology↗

bioRxiv2023

Comparative electric and ultrastructural studies of cable bacteria reveal new components of conduction machinery

Cable bacteria encompass at least two genera, and they are known to vary greatly in habitat preferences and filament thickness. We systematically investigated variations and similarities in cellular structures and electrical properties of different cable bacteria strains. Using SEM, TEM, STEM-EDX and ToF-SIMS, we characterized shared features of cable bacteria, such as inner and outer membranes, surface layer and cell junction architecture, as well as strain specific features, like the number and size of periplasmic conductive fibers (PCFs). Our data indicates that the PCFs are organized as loose stranded rope-like structures. With spatially resolved elemental analysis we detected nickel-containing co-factors within the PCF of cable bacteria strains in both genera suggesting a conserved conduction mechanism. Electrical conductivity of different cable bacteria strains showed a range of values covering three orders of magnitude indicating an unknown metabolic adaptation. Using cryogenic electron tomography we discovered multiple polar chemosensory arrays, abundant cytoplasmic inner membrane-attached vesicles (IMVs), polysomes and inner membrane invaginations that shed light on cable bacteria metabolism including complex motility control mechanisms, localized protein synthesis, and membrane remodeling. We propose that the IMVs discovered in this work are novel metabolic hubs closely connected to the unique conductive fiber structure of cable bacteria.

microbiology↗

bioRxiv2022

Syncytial nerve net in a ctenophore sheds new light on the early evolution of nervous systems

A fundamental breakthrough in neurobiology has been the formulation of the neuron doctrine by Santiago Ramon y Cajal, which states that the nervous system is composed of discrete individual cells. Electron microscopy later confirmed the doctrine and allowed the identification of synaptic connections. Here we use volume electron microscopy and 3D reconstructions to characterize the nerve net of a cydippid-phase ctenophore, belonging to one of the earliest-branching animal lineages. We found that neurons of its subepithelial nerve net do not follow Cajals neuron doctrine but instead show a continuous plasma membrane forming a syncytium. This is more similar to the reticulate theory of the nervous system put forward by Camillo Golgi. Additionally, we were able to identify new sensory cell types and describe simple neuro-sensory circuits for cydippid-phase ctenophores. Together with the ctenophore-specific synaptic architecture and the presence of an extensive repertoire of lineage-specific neuropeptides our morphological data provide substantial evidence for the independent evolution of the nervous system of ctenophores and the remaining animals.

evolutionary biology↗