Biological electron transport is classically thought to occur over nanometre distances, yet recent studies suggest that electrical currents can run along centimetre-long cable bacteria. The phenomenon remains elusive, however, as currents have not been directly measured, nor have the conductive structures been identified. Here we demonstrate that cable bacteria conduct electrons over centimetre distances via highly conductive fibres embedded in the cell envelope. Direct electrode measurements reveal nanoampere currents in intact filaments up to 10.1 mm long (>2000 adjacent cells). A network of parallel periplasmic fibres displays a high conductivity (up to 79 S cm−1), explaining currents measured through intact filaments. Conductance rapidly declines upon exposure to air, but remains stable under vacuum, demonstrating that charge transfer is electronic rather than ionic. Our finding of a biological structure that efficiently guides electrical currents over long distances greatly expands the paradigm of biological charge transport and could enable new bio-electronic applications.
Multicellularity is a key evolutionary innovation, leading to coordinated activity and resource sharing among cells, which generally occurs via the physical exchange of chemical compounds. However, filamentous cable bacteria display a unique metabolism in which redox transformations in distant cells are coupled via long-distance electron transport rather than an exchange of chemicals. This challenges our understanding of organismal functioning, as the link among electron transfer, metabolism, energy conservation, and filament growth in cable bacteria remains enigmatic. Here, we show that cells within individual filaments of cable bacteria display a remarkable dichotomy in biosynthesis that coincides with redox zonation. Nanoscale secondary ion mass spectrometry combined with 13C (bicarbonate and propionate) and 15N-ammonia isotope labeling reveals that cells performing sulfide oxidation in deeper anoxic horizons have a high assimilation rate, whereas cells performing oxygen reduction in the oxic zone show very little or no label uptake. Accordingly, oxygen reduction appears to merely function as a mechanism to quickly dispense of electrons with little to no energy conservation, while biosynthesis and growth are restricted to sulfide-respiring cells. Still, cells can immediately switch roles when redox conditions change, and show no differentiation, which suggests that the “community service” performed by the cells in the oxic zone is only temporary. Overall, our data reveal a division of labor and electrical cooperation among cells that has not been seen previously in multicellular organisms.
Enzyme-based electrochemical biosensors are an inspiration for the development of (bio)analytical techniques. However, the instability and reproducibility of the reactivity of enzymes, combined with the need for chemical reagents for sensing remain challenges for the construction of useful devices. Here we present a sensing strategy inspired by the advantages of enzymes and photoelectrochemical sensing, namely the integration of aerobic photocatalysis and electrochemical analysis. The photosensitizer, a bioinspired perfluorinated Zn phthalocyanine, generates singlet-oxygen from air under visible light illumination and oxidizes analytes, yielding electrochemically-detectable products while resisting the oxidizing species it produces. Compared with enzymatic detection methods, the proposed strategy uses air instead of internally added reactive reagents, features intrinsic baseline correction via on/off light switching and shows C-F bonds-type enhanced stability. It also affords selectivity imparted by the catalytic process and nano-level detection, such as 20 nM amoxicillin in μl sample volumes.
Since their inception, DNA aptamers were regarded as the turning point for biochemical sensing in real samples; however up to now their promises are far from being fulfilled. Especially aptamers for small molecules pose a challenge for both selection and characterization. The lack of a universally accepted and robust quality control protocol for the characterization of aptamer performances coupled with the observation of inconsistent data sets in literature, prompted us to address the issue comparing different analytical methodologies to validate (or disprove) the binding capabilities of aptamer sequences. We chose three aptamers for ampicillin, a β-Lactam antibiotic; used several detection strategies described in literature. The colorimetric gold nanoparticles (AuNPs) assay used in the original paper describing the aptamer sequences was repeated with conflicting results. The three sequences were then tested with three different instrumental techniques to assess their Kd and binding mechanism in homogeneous solutions. Coupling the thermodynamic data obtained with Isothermal Titration Calorimetry (ITC) with the structural information on the binding event given by Native Electro Spray Ionization Mass spectrometry (Native ESI-MS) and 1H-NMR it was possible to verify that the three sequences do not show any specific binding with the target ampicillin. To verify the influence of the AuNPs on the binding event, the experiments were repeated in presence of AuNPs both with ITC and 1H-NMR, again without any results. By offering a cross-referenced and robust analitycal approach to aptamer characterization we aim at elucidating the potentialities of aptamer for small organic molecules, especially when ultrasensitive analytical application are involved
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