Cable bacteria: widespread filamentous electroactive microorganisms protecting environments

Suppressing sediment nutrient release via electrokinetic drainage of porewater: apparent paradox and underlying mechanisms

Sediment nitrogen and phosphorus release drives internal eutrophication in many waterbodies, with nutrient-rich porewater serving as the key pathway for nutrient transfer to overlying water. In this study, electrokinetic geosynthetics (EKGs) were employed as electrodes to drain porewater and suppress sediment nutrient release. Five treatment groups with varying voltage gradients and power-on modes were tested. Nitrogen and phosphorus were primarily drained as ammonium (NH4+) and phosphate (PO43-), respectively. The total nitrogen removal from sediments was 16-20 times greater than that of phosphorus; however, the increase in nitrogen concentration in the overlying water was also nearly 10 times higher than that of phosphorus. This apparent paradox likely resulted from two key mechanisms. On one hand, NH4+ was rapidly mobilized and drained under the electric field, whereas PO43- required a series of acidification reactions before it could be released and transported. On the other hand, even when phosphate entered the overlying water, it was readily re-adsorbed or precipitated by the sediment, while nitrogen continued to accumulate through ongoing biogeochemical processes. Despite the differing removal efficiencies, electrokinetic drainage of porewater reduced sediment nutrient content in situ and suppressed nutrient enrichment in the overlying water, offering a promising strategy for the mitigation of internal eutrophication.

Multidisciplinary methodologies used in the study of cable bacteria

Cable bacteria are a unique type of filamentous microorganism that can grow up to centimetres long and are capable of long-distance electron transport over their entire lengths. Due to their unique metabolism and conductive capacities, the study of cable bacteria has required technical innovations, both in adapting existing techniques and developing entirely new ones. This review discusses the existing methods used to study eight distinct aspects of cable bacteria research, including the challenges of culturing them in laboratory conditions, performing physical and biochemical extractions, and analysing the conductive mechanism. As cable bacteria research requires an interdisciplinary approach, methods from a range of fields are discussed, such as biogeochemistry, genomics, materials science, and electrochemistry. A critical analysis of the current state of each approach is presented, highlighting the advantages and drawbacks of both commonly used and emerging methods.

Cable bacteria: Living electrical conduits for biogeochemical cycling and water environment restoration

Since the discovery of multicellular cable bacteria in marine sediments in 2012, they have attracted widespread attention and interest due to their unprecedented ability to generate and transport electrical currents over centimeter-scale long-range distances. The cosmopolitan distribution of cable bacteria in both marine and freshwater systems, along with their substantial impact on local biogeochemistry, has uncovered their important role in element cycling and ecosystem functioning of aquatic environments. Considerable research efforts have been devoted to the potential utilization of cable bacteria for various water management purposes during the past few years. However, there lacks a critical summary on the advances and contributions of cable bacteria to biogeochemical cycles and water environment restoration. This review aims to provide an up-to-date and comprehensive overview of the current research on cable bacteria, with a particular view on their participation in aquatic biogeochemical cycles and promising applications in water environment restoration. It systematically analyzes (i) the global distribution of cable bacteria in aquatic ecosystems and the major environmental factors affecting their survival, diversity, and composition, (ii) the interactive associations between cable bacteria and other microorganisms as well as aquatic plants and infauna, (iii) the underlying role of cable bacteria in sedimentary biogeochemical cycling of essential elements including but not limited to sulfur, iron, phosphorus, and nitrogen, (iv) the practical explorations of cable bacteria for water pollution control, greenhouse gas emission reduction, aquatic ecological environment restoration, as well as possible combinations with other water remediation technologies. It is believed to give a step-by-step introduction to progress on cable bacteria, highlight key findings, opportunities and challenges of using cable bacteria for water environment restoration, and propose directions for further exploration.