Groundwater electro-bioremediation via diffuse electro-conductive zones: A critical review.

Microbial electrochemical technologies (MET) can remove a variety of organic and inorganic pollutants from contaminated groundwater. However, despite significant laboratory-scale successes over the past decade, field-scale applications remain limited. We hypothesize that enhancing the electrochemical conductivity of the soil surrounding electrodes could be a groundbreaking and cost-effective alternative to deploying numerous high-surface-area electrodes in short distances.

Interaction of living cable bacteria with carbon electrodes in bioelectrochemical systems.

Unlabelled: Cable bacteria are filamentous bacteria that couple the oxidation of sulfide in sediments to the reduction of oxygen via long-distance electron transport over centimeter distances through periplasmic wires. However, the capability of cable bacteria to perform extracellular electron transfer to acceptors, such as electrodes, has remained elusive. In this study, we demonstrate that living cable bacteria actively move toward electrodes in different bioelectrochemical systems.

Accelerated nitrogen cycling on Mediterranean seagrass leaves at volcanic CO vents.

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 at a volcanic CO vent near Ischia Island (Italy), with OA affecting both N gain and loss while the epiphytic microbial community structure remains largely unaffected.

Examining the resistance and resilience of anode-respiring Shewanella oneidensis biohybrid using microsensors.

Immobilizing electro-active microbes within polymer matrices (thereby forming biohybrids) is a promising approach to accelerate microbial attachment to electrodes and increase the biofilm robustness. However, little is known on the fine scale chemical environment that develops within the electro-active biohybrids. Herein, we develop a biohybrid by immobilizing a culture of Shewanella oneidensis MR1 in agar matrix on the surface of a graphite electrode poised at +0.

Microsensor for total dissolved sulfide (TDS).

Total Dissolved Sulfide (TDS) concentrations can either be derived from simultaneous measurement of pH and one of the sulfide species or determined indirectly in samples following an acidification step. Here we report a microsensor that allows for direct measurement of TDS in aquatic media without the need for pH monitoring. An acidic chamber placed in front of a commercial, amperometric HS microsensor allows for the in-situ conversion of dissolved ionic sulfide species to HS, which in turn is oxidized at the transducer anode.

Nested interactions between chemosynthetic lucinid bivalves and seagrass promote ecosystem functioning in contaminated sediments.

In seagrass sediments, lucinid bivalves and their chemoautotrophic bacterial symbionts consume HS, relying indirectly on the plant productivity for the presence of the reduced chemical. Additionally, the role of lucinid bivalves in N provisioning to the plant (through N fixation by the symbionts) was hypothesized. Thus, lucinids may contribute to sediment detoxification and plant fitness.

Snorkels enhance alkanes respiration at ambient and increased hydrostatic pressure (10 MPa) by either supporting the TCA cycle or limiting alternative routes for acetyl-CoA metabolism.

The impact of piezosensitive microorganisms is generally underestimated in the ecology of underwater environments exposed to increasing hydrostatic pressure (HP), including the biodegradation of crude oil components. Yet, no isolated pressure-loving (piezophile) microorganism grows optimally on hydrocarbons, and no isolated piezophile at all has a HP optimum <10 MPa (e.g.

The role of epiphytes in seagrass productivity under ocean acidification.

Ocean Acidification (OA), due to rising atmospheric CO, can affect the seagrass holobiont by changing the plant's ecophysiology and the composition and functioning of its epiphytic community. However, our knowledge of the role of epiphytes in the productivity of the seagrass holobiont in response to environmental changes is still very limited. CO vents off Ischia Island (Italy) naturally reduce seawater pH, allowing to investigate the adaptation of the seagrass Posidonia oceanica L.

Dissimilatory nitrate reduction by a freshwater cable bacterium.

Cable bacteria (CB) are filamentous Desulfobulbaceae that split the energy-conserving reaction of sulfide oxidation into two half reactions occurring in distinct cells. CB 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.

Effect of salinity on cable bacteria species composition and diversity.

Cable bacteria (CB) are Desulfobulbaceae that couple sulphide oxidation to oxygen reduction over centimetre distances by mediating electric currents. Recently, it was suggested that the CB clade is composed of two genera, Ca. Electronema and Ca.

Zebra Mussel Holobionts Fix and Recycle Nitrogen in Lagoon Sediments.

Bivalves are ubiquitous filter-feeders able to alter ecosystems functions. Their impact on nitrogen (N) cycling is commonly related to their filter-feeding activity, biodeposition, and excretion. A so far understudied impact is linked to the metabolism of the associated microbiome that together with the host constitute the mussel's holobiont.

Meiofauna improve oxygenation and accelerate sulfide removal in the seasonally hypoxic seabed.

Oxygen depleted areas are widespread in the marine realm. Unlike macrofauna, meiofauna are abundant in hypoxic sediments. We studied to what extent meiofauna affect oxygen availability, sulfide removal and microbial communities.

Uncovering diversity and metabolic spectrum of animals in dead zone sediments.

Ocean deoxygenation driven by global warming and eutrophication is a primary concern for marine life. Resistant animals may be present in dead zone sediments, however there is lack of information on their diversity and metabolism. Here we combined geochemistry, microscopy, and RNA-seq for estimating taxonomy and functionality of micrometazoans along an oxygen gradient in the largest dead zone in the world.

Electrogenic sulfide oxidation mediated by cable bacteria stimulates sulfate reduction in freshwater sediments.

Cable bacteria are filamentous members of the Desulfobulbaceae family that oxidize sulfide with oxygen or nitrate by transferring electrons over centimeter distances in sediments. Recent studies show that freshwater sediments can support populations of cable bacteria at densities comparable to those found in marine environments. This is surprising since sulfide availability is presumably low in freshwater sediments due to sulfate limitation of sulfate reduction.

Parallel artificial and biological electric circuits power petroleum decontamination: The case of snorkel and cable bacteria.

Degradation of petroleum hydrocarbons (HC) in sediments is often limited by the availability of electron acceptors. By allowing long-distance electron transport (LDET) between anoxic sediments and oxic overlying water, bioelectrochemical snorkels may stimulate the regeneration of sulphate in the anoxic sediment thereby accelerating petroleum HC degradation. Cable bacteria can also mediate LDET between anoxic and oxic sediment layers and thus theoretically stimulate petroleum HC degradation.

Capping with activated carbon reduces nutrient fluxes, denitrification and meiofauna in contaminated sediments.

Sediment capping with activated carbon (AC) is an effective technique used in remediation of contaminated sediments, but the ecological effects on benthic microbial activity and meiofauna communities have been largely neglected. This study presents results from a 4-week experiment investigating the influence of two powdered AC materials (bituminous coal-based and coconut shell-derived) and one control material (clay) on biogeochemical processes and meiofauna in contaminated sediments. Capping with AC induced a 62-63% decrease in denitrification and a 66-87% decrease in dissimilatory nitrate reduction to ammonium (DNRA).

Transient bottom water oxygenation creates a niche for cable bacteria in long-term anoxic sediments of the Eastern Gotland Basin.

Cable bacteria have been reported in sediments from marine and freshwater locations, but the environmental factors that regulate their growth in natural settings are not well understood. Most prominently, the physiological limit of cable bacteria in terms of oxygen availability remains poorly constrained. In this study, we investigated the presence, activity and diversity of cable bacteria in relation to a natural gradient in bottom water oxygenation in a depth transect of the Eastern Gotland Basin (Baltic Sea).

Effect of settled diatom-aggregates on benthic nitrogen cycling.

The marine sediment hosts a mosaic of microhabitats. Recently it has been demonstrated that the settlement of phycodetrital aggregates can induce local changes in the benthic O distribution due to confined enrichment of organic material and alteration of the diffusional transport. Here, we show how this microscale O shift substantially affects benthic nitrogen cycling.

Electric coupling between distant nitrate reduction and sulfide oxidation in marine sediment.

Filamentous bacteria of the Desulfobulbaceae family can conduct electrons over centimeter-long distances thereby coupling oxygen reduction at the surface of marine sediment to sulfide oxidation in deeper anoxic layers. The ability of these cable bacteria to use alternative electron acceptors is currently unknown. Here we show that these organisms can use also nitrate or nitrite as an electron acceptor thereby coupling the reduction of nitrate to distant oxidation of sulfide.