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The discovery of cable bacteria has revolutionized our understanding of long-distance biological electron transfer and has provoked the study of their distribution. Cable bacteria are widely distributed in aquatic environments and exhibit superior adaptations at the oxic–anoxic interface. The physiology and available genomes of cable bacteria have provided insights into the factors that control cable bacteria distribution, facilitating the anticipation of their occurrence and management of their ecological benefits. Cable bacteria create redox gradients, alter sediment geochemistry and nutrient cycling, influence microbial activity and networks, and alleviate multiple anthropogenic problems. The impact of cable bacteria can extend to the atmosphere, and their ecological significance may be more far-reaching than was previously believed. Cable bacteria have been identified and detected worldwide since their discovery in marine sediments in Aarhus Bay, Denmark. Their activity can account for the majority of oxygen consumption and sulfide depletion in sediments, and they induce sulfate accumulation, pH excursions, and the generation of electric fields. In addition, they can affect the fluxes of other elements such as calcium, iron, manganese, nitrogen, and phosphorous. Recent developments in our understanding of the impact of cable bacteria on element cycling have revealed their positive contributions to mitigating environmental problems, such as recovering self-purification capacity, enhancing petroleum hydrocarbon degradation, alleviating phosphorus eutrophication, delaying euxinia, and reducing methane emission. We highlight recent research outcomes on their distribution, state-of-the-art findings on their physiological characteristics, and ecological contributions. [ABSTRACT FROM AUTHOR]

The ability of microorganisms to reduce structural Fe in minerals has become recognized as an important mechanism in the oxidation of pollutants in soils and sediments. To better understand the factors controlling the concentration of Fe(II) in natural deposits, samples of clayey till from sites near Havrebjerg and Sparresholm, Denmark, were incubated for up to 160 d with a combination of Pseudomonas bacteria strains. These strains were previously shown to reduce structural Fe(III) to Fe(II) in smectites. According to Eh, pH, microbial activity, and structural Fe(II) content, the incubation could be separated into four phases of which the second phase (from 4 to 10 d after inoculation) generated the most structural Fe(II). Microbial activity increased the structural Fe(II) content from approximately 10% to 20–34% of total clay Fe, a lower level than that obtained for chemically reduced subsamples (76–79%), but more similar to values typical of unweathered tills of Denmark (about 50%). In addition to microbial activity, the particle size (fine or coarse clay) and the Fe(II) content of the clay minerals prior to incubation were very important factors affecting the extent of Fe reduction. The results indicate that structural Fe in clay minerals of clayey till is very reactive and can undergo extensive in situ redox cycling. Electron transfer to structural Fe(III) of the weathered, oxidized clay minerals may renew natural redox barriers in imperfectly drained soils and sediments and thereby control geochemical processes. [ABSTRACT FROM AUTHOR]