Cable bacteria form a group of multicellular prokaryotes that enable electron transfer over centimeter-scale distances within marine and freshwater sediments. To this end, the periplasm of these filamentous bacteria contains specialized conductive fibers, which extend along the full length of each filament and incorporate a novel Ni-containing NiBiD cofactor. Currently, the cable bacteria include two recognized genera, Candidatus Electrothrix and Candidatus Electronema, but the genetic and morphological diversity within the clade remains underexplored. Here, we report the isolation and characterization of a novel cable bacteria species from an intertidal estuarine mudflat within Yaquina Bay (Oregon, USA). A clonal enrichment culture of a single strain (designated YB6) was generated, and filaments were subjected to genomic, morphological, spectroscopic, and electrical characterization. Strain YB6 shares key physiological traits with other cable bacteria, such as long-distance electron conduction and the presence of the nickel bis(dithiolene) cofactor. At the same time, YB6 exhibits distinctive morphological features, including pronounced surface ridges that are up to three times wider than in other cable bacteria. Additionally, filaments are extensively enveloped by extracellular sheaths. Genomic analysis reveals that strain YB6 harbors metabolic pathways and genes found in both the Ca. Electrothrix and Ca. Electronema genera. Phylogenetic and phylogenomic analyses indicate that strain YB6 represents a novel species (average nucleotide identity <95%) that forms an early branch within the Ca. Electrothrix clade. The proposed name is Ca. Electrothrix yaqonensis sp. nov., honoring the Yako’n tribe of Native Americans whose ancestral lands encompassed Yaquina Bay. ... Read more

Cable bacteria are filamentous, multicellular microorganisms that display an exceptional form of biological electron transport across centimeter-scale distances. Currents are guided through a network of nickel-containing protein fibers within the cell envelope. Still, the mechanism of long-range conduction remains unresolved. Here, we characterize the conductance of the fiber network under dry and wet, physiologically relevant, conditions. Our data reveal that the fiber conductivity is high (median value: 27 S cm⁻¹; range: 2 to 564 S cm⁻¹), does not show any redox signature, has a low thermal activation energy (E_a = 69 ± 23 meV), and is not affected by humidity or the presence of ions. These features set the nickel-based conduction mechanism in cable bacteria apart from other known forms of biological electron transport. As such, conduction resembles that of an organic semi-metal with a high charge carrier density. Our observation that biochemistry can synthesize an organo-metal-like structure opens the way for novel bio-based electronic technologies. ... Read more