Final Report Summary - SEDBIOGEOCHEM2.0 (Hardwiring the ocean floor: the impact of microbial electrical circuitry on biogeochemical cycling in marine sediments)
Electron transfer is fundamental to life, and as a consequence, biological systems have evolved the capacity to generate electrical currents across a range of spatial scales. In photosynthesis and cellular respiration, electrons are channelled over nanometre distances, through quantum-mechanical tunnelling between redox co-factors embedded in membrane bound enzymes. Similarly, dissimilatory metal-reducing bacteria are known to develop conductive appendages, known as “nanowires”, which are capable of shuttling electrons to solid electron acceptors outside the cell, thus enabling electron transport over longer distances, up to 10 micrometers. Recently, this known length scale of biological electron transmission has been extended by three orders of magnitude, via the discovery of cable bacteria, which induce electrical currents bridging centimetre-scale distances. Experiments demonstrate that that electrons are passed on from cell to cell along the longitudinal axis of bacterial filaments. This discovery entails that microbial mediated electron transport takes place over vastly greater distances than previously recognized, as it extends the known length scale of biological electron transmission by three orders of magnitude.
The capability of cable bacteria to perform long-distance electron transport makes that the seafloor operates like a natural battery, and the SEDBIOGEOCHEM2.0 project has examined and quantified the important implications for the biogeochemical cycling in natural environments. To this end, the project has carried out research on three fronts: field studies, laboratory experiments, and model development. Prior to the start of the project, cable bacteria had only been grown in the laboratory, and it was unclear how important they were for natural biogeochemical cycling in the seafloor. During the ERC project, we were able to demonstrate that cable bacteria are active in a range of natural marine habitats (salt marshes, mangroves, seasonal hypoxic basins) across the globe. Moreover, laboratory experiments carried under controlled conditions, unraveled the carbon metabolism of the cable bacteria and demonstrated how the growth and development of a cable bacteria population strongly impacts the biogeochemical cycling of various elements (carbon, calcium, iron, phosphorus...) in marine sediments. In addition, we have demonstrated that cable bacteria induce rapid redox teleconnections in the seafloor, thus allowing redox signals to penetrate the seafloor over a time scale of minutes, rather than days or weeks. Finally, we developed a new computer simulation model that is capable of quantitatively simulating the solute depth profiles and biogeochemical transformations in electro-active marine sediments.
The capability of cable bacteria to perform long-distance electron transport makes that the seafloor operates like a natural battery, and the SEDBIOGEOCHEM2.0 project has examined and quantified the important implications for the biogeochemical cycling in natural environments. To this end, the project has carried out research on three fronts: field studies, laboratory experiments, and model development. Prior to the start of the project, cable bacteria had only been grown in the laboratory, and it was unclear how important they were for natural biogeochemical cycling in the seafloor. During the ERC project, we were able to demonstrate that cable bacteria are active in a range of natural marine habitats (salt marshes, mangroves, seasonal hypoxic basins) across the globe. Moreover, laboratory experiments carried under controlled conditions, unraveled the carbon metabolism of the cable bacteria and demonstrated how the growth and development of a cable bacteria population strongly impacts the biogeochemical cycling of various elements (carbon, calcium, iron, phosphorus...) in marine sediments. In addition, we have demonstrated that cable bacteria induce rapid redox teleconnections in the seafloor, thus allowing redox signals to penetrate the seafloor over a time scale of minutes, rather than days or weeks. Finally, we developed a new computer simulation model that is capable of quantitatively simulating the solute depth profiles and biogeochemical transformations in electro-active marine sediments.