Surface characterisation reveals substrate suitability for Cyanobacterial phototaxis

Cyanobacteria respond to light stimulation, activating localized assembly of type IV pili for motility. The resulting phototactic response is highly dependent on the nature of the incoming light stimulus, and the final motility parameters depend on the surface properties. Conventionally, phototaxis studies are carried out on hydrogel surfaces, such as agarose, with surface properties, that vary in time due to experimental conditions. This study considers five substrates, widely utilized in microfluidic technology, to identify the most suitable alternative for performing reliable and repeatable phototaxis assays. The surfaces are characterized via a contact angle goniometer to determine the surface energy, white light interferometry for roughness, zeta-potentials and AFM force distance curves for charge patterns, and XPS for surface composition. Cell motility assays showed 1.25 times increment on surfaces with a water contact angle of 80 compared to a reference glass surface. To prove that motility can be enhanced, polydimethylsiloxane (PDMS) surfaces were plasma treated to alter their surface wettability. The motility on the plasma-treated PDMS showed similar performance as for glass surfaces. In contrast, untreated PDMS surfaces displayed close to zero motility. We also describe the force interctions of cells with the test surfaces using DLVO (Derjaguin-Landau-Verwey-Overbeek) and XDLVO (extended DLVO) theories. The computed DLVO/XDLVO force-distance curves are compared with those obtained using atomic force microscopy. Our findings show that twitching motility on tested surfaces can be described mainly from adhesive forces and hydrophobicity/hydrophilicity surface properties

Editorial: Advances in the environmental distribution of less studied elements

International audienceThis Research Topic focused on the advancements in our understanding of theenvironmental processes governing the transport and fate of several elements within naturalbiogeochemical cycles. The target elements were a group characterized by potentialenvironmental impacts, including emerging contaminants (e.g., critical elements) andradionuclides

Fractionation of inherited and spiked antimony (Sb) in fluvial/estuarine bulk sediments: Unexpected anomalies in parallel selective extraction protocols

Selective extractions are widely used in sediment, soil and sludge samples to assess trace element carrier phases, mobility and potential bioaccessibility. Commonly used selective parallel extractions were applied to natural and isotopically-labelled bulk sediments from the Gironde fluvial-estuarine system and the Rhône River (France) to determine the solid phase fractionation of antimony (Sb), a priority contaminant in EU and US regulations and an important radionuclide in decay series occurring in the environment after nuclear power plant accidents. Antimony fractions obtained from several, parallel selective extraction solutions targeting Fe/Mn oxides (i.e., hydroxylamine-, oxalate- and ascorbate-based, herein assigned as fractions from “F2” solutions) and acid-soluble operationally defined phases (HCl- and HNO3-based, herein assigned as fractions from “F4” solutions) were compared (i) between each other's, and (ii) with those of other trace elements (Co, Cu, Ni, Pb, Zn, Th and U) in the same extractions. The solid fractionation of inherited Sb and spiked Sb was studied by applying a complete set of parallel selective extractions to isotopically-labelled sediments of the Gironde Estuary. Results suggest protocol-related and sediment-dependent anomalies in Sb selective extractions, compared to results expected from the operationally-defined extraction scheme and obtained for other trace elements. In fact, Sb fractions extracted with oxalate- and ascorbate-based solutions were greater than acid-soluble fractions (1M HCl and 1M HNO3) in the Garonne/Gironde fluvial estuarine sediments. A similar anomaly occurred for oxalate-based extractions of Sb in Rhône River sediments. These observations suggest that reducing conditions and the presence of strongly complexing organic ligands in the environment may mobilise respectively 2-fold and ~5-fold more Sb from natural bulk sediment and from sediments spiked with isotopically-labelled Sb than the acid-soluble fraction, usually used to assess the reactive, potentially bioaccessible fractions. The underestimation of the reactive, potentially bioaccessible fractions of Sb may bias the environmental interpretation of Sb solid fractionation and should be taken into account when assessing stable Sb cycles and Sb radionuclide dispersion scenarios in continent-ocean transition systems

Historical mass balance of cadmium decontamination trends in a major European continent-ocean transition system: Case study of the Gironde Estuary

Despite the effective remediation efforts following the end of the metallurgic activity thirty years ago upstream the Lot River watershed, the levels of cadmium (Cd) accumulated in wild oysters from the downstream Gironde Estuary still exceed nowadays the admissible human consumption limit (5 mg/kg, d.w.). The main goal of this work is to quantify the role of sediments as long-term intra-estuarine sources or sinks of Cd and the transport of this contaminant towards the estuary mouth taking as case study the example of the highly turbid Gironde Estuary. The original estimation for the annual net fluxes of the suspended particulate matter ( and particulate Cd () presented in this work between 1990 and 2020 indicates that 80% of the Cd discharged into the ocean is in dissolved form (Cdd). The values of vary proportionally to those of and ranged between 0.1 and 1.4 t/y, with a ten-year average decreasing from 0.8 to 0.6 t/y for the past 30 years. The differences between ten-year total (Cdp + Cdd) gross and net fluxes show that Cd has effectively been stored in estuarine sediments. This Cd storage was of about 43, 22 and 13 t for the 1990s, 2000s and 2010s, respectively. However, during years of low gross fluxes, estuarine sediments act as additional, secondary sources of bio-available/dissolved Cd into the water column, potentially relating to the continued observations of high Cd concentrations in wild oysters at the estuary mouth. In addition to the natural solubility of Cdp along the salinity and turbidity gradients of the estuary, natural and anthropogenic remobilization of bottom sediment particles further contribute to its mobilization from the particle phase, along with other numerous inorganic/organic pollutants. The mass balances presented in this work could support a new sediment management policy potentially more beneficial to the estuarine ecosystem

Tellurium and selenium sorption kinetics and solid fractionation under contrasting estuarine salinity and turbidity conditions

International audienceTellurium (Te) is a Technology Critical Element (TCE) and a relevant product of nuclear fission. It has an unknown environmental biogeochemical cycle, mostly related to current analytical challenges in measuring its ultra-trace dissolved concentrations in complex environmental matrices. It is therefore generally compared to its geochemical pair selenium (Se), which shows a narrow range between diet essentiality and toxicity properties. Batch experiments using isotopically-labelled stable Te and Se were performed with fresh suspended particulate matter (SPM) from the fluvial part of the Gironde Estuary, simulating both estuarine salinity (S = 0 vs S = 32) and turbidity (100 mg L−1 vs 1000 mg L−1) gradients to understand the importance of the particulate phases in Te reactivity under estuarine conditions and verify the resemblance to Se behaviour. These experiments addressed sorption kinetics, sorption isotherms and fractionation from selective extractions of final equilibrated SPM. Results showed a strong, salinity-independent affinity of Te for the particulate phases (log10 Kd ~ 4.9 L kg−1), following a Langmuir-type isotherm. Contrastingly, Se adsorbs clearly less to estuarine SPM (log10 Kd ~ 2.5 L kg−1), following a Freundlich-type isotherm. Both isotherms and selective extractions highlighted differences between Te and Se sequestration. Selective extractions suggested higher mobility of particulate Se in contrast to Te. Based on these results the paper sets a first dispersion scenario on the environmental fate of radioactive Te and Se after hypothetical nuclear power plant accidental releases in coastal aquatic systems such as the Garonne-Gironde fluvial-estuarine system

Relationship between decalcification and pH_F for an acute OA response.

<p>Relationship between mean decalcified surfaces (%) in <i>P. pavonica</i> and coastal pH_F values for all sites and times (n = 15): (RH) ‘La Restinga harbour’, (R) ‘La Restinga’, (AB) ‘Arenas Blancas’, (CM) ‘Charco Manso’ and (C) ‘La Cometa’ (control). s_est stands for standard error of estimate.</p

Effects of Ocean Acidification on the Brown Alga <i>Padina pavonica</i>: Decalcification Due to Acute and Chronic Events

<div><p>Since the industrial revolution, anthropogenic CO₂ emissions have caused ocean acidification, which particularly affects calcified organisms. Given the fan-like calcified fronds of the brown alga <i>Padina pavonica</i>, we evaluated the acute (short-term) effects of a sudden pH drop due to a submarine volcanic eruption (October 2011–early March 2012) affecting offshore waters around El Hierro Island (Canary Islands, Spain). We further studied the chronic (long-term) effects of the continuous decrease in pH in the last decades around the Canarian waters. In both the observational and retrospective studies (using herbarium collections of <i>P. pavonica</i> thalli from the overall Canarian Archipelago), the percent of surface calcium carbonate coverage of <i>P. pavonica</i> thalli were contrasted with oceanographic data collected either <i>in situ</i> (volcanic eruption event) or from the ESTOC marine observatory data series (herbarium study). Results showed that this calcified alga is sensitive to acute and chronic environmental pH changes. In both cases, pH changes predicted surface thallus calcification, including a progressive decalcification over the last three decades. This result concurs with previous studies where calcareous organisms decalcify under more acidic conditions. Hence, <i>Padina pavonica</i> can be implemented as a bio-indicator of ocean acidification (at short and long time scales) for monitoring purposes over wide geographic ranges, as this macroalga is affected and thrives (unlike strict calcifiers) under more acidic conditions.</p></div