Electrogenic sulfur oxidation mediated by cable bacteria and its ecological effects.

At the sediment-water interfaces, filamentous cable bacteria transport electrons from sulfide oxidation along their filaments towards oxygen or nitrate as electron acceptors. These multicellular bacteria belonging to the family Desulfobulbaceae thus form a biogeobattery that mediates redox processes between multiple elements. Cable bacteria were first reported in 2012. In the past years, cable bacteria have been found to be widely distributed across the globe. Their potential in shaping the surface water environments has been extensively studied but is not fully elucidated. In this review, the biogeochemical characteristics, conduction mechanisms, and geographical distribution of cable bacteria, as well as their ecological effects, are systematically reviewed and discussed. Novel insights for understanding and applying the role of cable bacteria in aquatic ecology are summarized.

Cable Bacteria Skeletons as Catalytically Active Electrodes.

Cable bacteria are multicellular, filamentous bacteria that use internal conductive fibers to transfer electrons over centimeter distances from donors within anoxic sediment layers to oxygen at the surface. We extracted the fibers and used them as free-standing bio-based electrodes to investigate their electrocatalytic behavior. The fibers catalyzed the reversible interconversion of oxygen and water, and an electric current was running through the fibers even when the potential difference was generated solely by a gradient of oxygen concentration. Oxygen reduction as well as oxygen evolution were confirmed by optical measurements. Within living cable bacteria, oxygen reduction by direct electrocatalysis on the fibers and not by membrane-bound proteins readily explains exceptionally high cell-specific oxygen consumption rates observed in the oxic zone, while electrocatalytic water oxidation may provide oxygen to cells in the anoxic zone.

Syncytial nerve net in a ctenophore adds insights on the evolution of nervous systems.

A fundamental breakthrough in neurobiology has been the formulation of the neuron doctrine by Santiago Ramón y Cajal, which stated that the nervous system is composed of discrete cells. Electron microscopy later confirmed the doctrine and allowed the identification of synaptic connections. In this work, we used volume electron microscopy and three-dimensional reconstructions to characterize the nerve net of a ctenophore, a marine invertebrate that belongs to one of the earliest-branching animal lineages. We found that neurons in the subepithelial nerve net have a continuous plasma membrane that forms a syncytium. Our findings suggest fundamental differences of nerve net architectures between ctenophores and cnidarians or bilaterians and offer an alternative perspective on neural network organization and neurotransmission.