Biology subjects

Marzocchi, U.

Publications and source records attributed to Marzocchi, U..

4 recordsLinked to original sources

bioRxiv2025

Extracellular electron transfer in cable bacteria enables growth rates comparable to aerobic respiration

Cable bacteria are filamentous sulphide-oxidisers performing long-distance electron transfer in redox-stratified sediments by transporting electrons over centimetre-scale distances to reduce oxygen. Here, we show that the freshwater cable bacterium Electronema aureum GS can respire insoluble electron acceptors under anoxic conditions via a versatile extracellular electron transfer (EET) system, supporting growth rates comparable to those under aerobic conditions. Using electrochemical and molecular biology analyses, we demonstrate that E. aureum GS engages in both direct and mediated electron transfer to electrodes, including at +600 mV vs. Ag/AgCl--an unusually high redox potential typically not accessed by electroactive bacteria. Two distinct cell-surface redox components were identified, which are metal-dependent, pH-sensitive, and heat-labile, consistent with outer-membrane-localised cytochromes. Moreover, the redox shuttle riboflavin accumulated extracellularly and enhanced current production in bioelectrochemical systems, indicating a role for soluble mediators in cable bacteria. Together, these findings reveal a previously unrecognised respiratory flexibility in E. aureum GS and highlight EET as a key alternative strategy for energy conservation in fluctuating redox environments.

microbiology↗

bioRxiv2023

Electrically controlled interaction between cable bacteria and carbon electrodes

Cable bacteria couple the oxidation of sulphide in sediments to the reduction of oxygen via long-distance electron transfer through periplasmic wires. While direct electron transfer between cable bacteria cells belonging to the same filament is a well-known phenomenon, electron transfer from the filament to electrodes has remained elusive. In this study, we demonstrate that living cable bacteria are attracted to electrodes in different bioelectrochemical systems. Carbon felt and carbon fibre electrodes poised at +200 mV against an Ag/AgCl reference attracted live cable bacteria from the sediment. When the applied potential was switched off, cable bacteria retracted from the electrode. qPCR and scanning electron microscopy corroborated this finding and revealed cable bacteria adhered onto the electrode surface. These experiments raise new possibilities to cultivate cable bacteria and utilise them for important applications in bioelectrochemical systems.

microbiology↗

bioRxiv2023

Accelerated Nitrogen Cycling on Seagrass Leaves in a High-CO2 World

Seagrass meadows form highly productive and diverse ecosystems in coastal areas worldwide, where they are increasingly exposed to ocean acidification (OA). Efficient nitrogen (N) cycling and uptake are essential to maintain plant productivity, but the effects of OA on N transformations in these systems are poorly understood. Here we show that complete N cycling occurs on leaves of the Mediterranean seagrass Posidonia oceanica, with OA affecting both N gain and loss while the prokaryotic community structure remains largely unaffected. Daily leaf-associated N2 fixation contributed to 35% of the plants N demand under ambient pH, whereas it contributed to 45% under OA. Nitrification potential was only detected under OA, and N-loss via N2 production increased, although the balance remained decisively in favor of enhanced N gain. Our work highlights the role of the N-cycling microbiome in seagrass adaptation to OA, with key N transformations accelerating towards increased N gain.

ecology↗

bioRxiv2020

Dissimilatory Nitrate Reduction To Ammonium In The Cable Bacterium Ca. Electronema Sp. GS

Cable bacteria are filamentous Desulfobulbaceae that split the energy-conserving reaction of sulphide oxidation into two half reactions occurring in distinct cells. Cable bacteria can use nitrate, but the reduction pathway is unknown, making it difficult to assess their direct impact on the N-cycle. Here we show that the freshwater cable bacterium Ca. Electronema sp. GS performs dissimilatory nitrate reduction to ammonium (DNRA). 15NO3--amended sediment with Ca. Electronema sp. GS showed higher rates of DNRA and nitrite production than sediment without Ca. Electronema sp. GS. Electron flux from sulphide oxidation, inferred from electric potential measurements, matched the electron flux needed to drive cable bacteria-mediated nitrate reduction. Ca. Electronema sp. GS expressed a complete nap operon for periplasmic nitrate reduction to nitrite, and genes encoding a periplasmic multiheme cytochrome (pMHC), homolog to a pMHC that can catalyse nitrite reduction to ammonium in Ca. Maribeggiatoa. Phylogenetic analysis suggests that the capacity for DNRA was acquired in multiple events through horizontal gene transfer from different organisms, before cable bacteria split into different salinity niches. The architecture of the nitrate reduction system suggests absence of energy conservation through oxidative phosphorylation, indicating that cable bacteria primarily conserve energy through the half reaction of sulfide oxidation.

microbiology↗