A new species of bacteria that functions like electrical wiring has recently been discovered on a brackish beach in Oregon. The species was named Candidatus Electrothrix yaqonensis in honor of the Yaquina tribe of Native Americans that once lived in and around Yaquina Bay, where the bacteria were found.
This species is a type of cable bacteria: rod-shaped microbes that are connected at both ends to one another to create a chain and which share an outer membrane, forming filaments several centimeters long. Cable bacteria are found in marine and freshwater sediments and, unusually among bacteria, are electrically conductive. This is due to their special metabolism, in which electrons generated by oxidizing sulfides in their deeper layers are sent to their surface layer, where they are received by oxygen and nitric acid.
The 25 species of cable bacteria known so far have been organized into two genera, Candidatus Electrothrix, which live in saltwater, and Candidatus Electronema, which live in fresh and brackish water. The new species discovered in this study has the genes and metabolic pathways of both the genera but is believed to be a bridge to an earlier branch of the Candidatus Electrothrix lineage, and so was classified as part of that genus.
The recently discovered species may provide new insights into how cable bacteria evolved and how they can function in diverse environments, Cheng Li, a postdoctoral researcher at Oregon State University and coauthor of the research, explained in a statement.
High Electrical Conductivity
Candidatus Electrothrix yaqonensis is distinct from existing cable bacteria in its appearance. Cable bacteria have outer shells that feature ridges, which spread out like mountains. The ridges of the new species are much thicker than those of previously known species, reaching an average thickness of about 228 nanometers, up to three times thicker than what has been seen before. The new species’ ridges are arranged in a spiral-like pattern on the surface of the filament, and their overall shape is more angular than that of other species.
But the most striking difference is that the new species’ filament is surrounded by a thick, transparent sheath. According to the authors of the paper outlining the discovery, this is a structure not previously seen. This sheath does not conduct electricity and is thought to protect the filament from the environment and foreign enemies.
Inside the new bacteria’s ridge is a fiber containing a nickel-centered metal complex, which functions as a “biological wire” that efficiently transports electrons along the filament. It is as if the structure itself was designed with an engineering intent.
The physical performance of the bacteria as a conductor is impressive. When the researchers placed microscopically isolated filaments on a gold electrode and applied a voltage, a graph showing the change in current and voltage produced a linear, symmetrical I-V curve—implying high electrical conductivity. The new species’ electrical resistance was approximately 370 kilo-ohms, which is equal to or better than that of known cable bacteria.
A Genetic Mosaic
Genomic analysis revealed that the new species has genetic features of both the Candidatus Electrothrix and Candidatus Electronema genera. This phenomenon, where genetically distinct material is intermingled within a single individual, is known as “mosaicism.” For example, this can be seen in the novel bacteria’s cytochrome, a type of protein involved in electron transport. Typically in the genus Candidatus Electrothrix, bacteria have a single heme (a complex composed of a divalent iron atom and a porphyrin). But the new species, like some other types of cable bacteria, is equipped with a cytochrome with two hemes.
This new species is also unique in the way it adapts to saline environments. Candidatus Electrothrix species, which live in saltwater, typically use an electron-transfer enzyme called “sodium-transporting NADH-quinone oxidoreductase (NQR)” to regulate osmotic pressure. But this enzyme is absent in Candidatus Electrothrix yaqonensis, which instead has several proteins— “sodium and proton exchange transporters (NHE)”—that exchange sodium ions and protons across the cell membrane. This is thought to be the result of adaptation to the unique environment of brackish water, where salinity fluctuates.
Further studies will reveal the mechanism of the unique sheath formation of Candidatus Electrothrix yaqonensis as well as the self-assembling process of its conductive fibers. According to the research team, this new species, because it combines high-electrical conductivity and environmental adaptability, has the potential to be used as a new material in the field of bioelectronics. Potentially it could help with the creation of biodegradable electronic devices and biosensors in the future. Its characteristics may also be useful for remediation of heavy metals and organic pollutants in sedimentary environments.
This story originally appeared on WIRED Japan and has been translated from Japanese.
