Effects of synthetic iron and aluminium oxide surface charge and hydrophobicity on the formation of bacterial biofilm

In this research, bacterial cell attachments to hematite, goethite and aluminium hydroxide were investigated. The aim was to study the effects of these minerals’ hydrophobicity and pH-dependent surface charge on the extent of biofilm formation using six genetically diverse bacterial strains: Rhodococcus spp. (RC92 & RC291), Pseudomonas spp. (Pse1 & Pse2) and Sphingomonas spp. (Sph1 & Sph2), which had been previously isolated from contaminated environments. The surfaces were prepared in a way that was compatible with the naturally occurring coating process in aquifers: deposition of colloidal particles from the aqueous phase. The biofilms were evaluated using a novel, in situ and non-invasive technique developed for this purpose. A manufactured polystyrene 12-well plate was used as the reference surface to be coated with synthesized minerals by deposition of their suspended particles through evaporation. Planktonic phase growth indicates that it is independent of the surface charge and hydrophobicity of the studied surfaces. The hydrophobic similarities failed to predict biofilm proliferation. Two of the three hydrophilic strains formed extensive biofilms on the minerals. The third one, Sph2, showed anomalies contrary to the expected electrostatic attraction between the minerals and the cell surface. Further research showed how the solution’s ionic strength affects Sph2 surface potential and shapes the extent of its biofilm formation; reducing the ionic strength from 200 mM to 20 mM led to a tenfold increase in the number of cells attached to hematite. This study provides a technique to evaluate biofilm formation on metal-oxide surfaces, under well-controlled conditions, using a simple yet reliable method. The findings also highlight that cell numbers in the planktonic phase do not necessarily show the extent of cell attachment, and thorough the physicochemical characterization of bacterial strains, substrata and the aquifer medium are fundamental to successfully implementing any bioremediation projects

Nanoscale channels on ectomycorrhizal-colonized chlorite: Evidence for plant-driven fungal dissolution

The roots of many trees in temperate and boreal forests are sheathed with ectomycorrhizal fungi (EMF) that extend into the soil, forming intimate contact with soil minerals, from which they absorb nutrient elements required by the plants and, in return, are supported by the organic carbon photosynthesized by the trees. While EMF are strongly implicated in mineral weathering, their effects on mineral surfaces at the nanoscale are less documented. In the present study, we investigated the effects of symbiotic EMF on the topography of a chlorite mineral using atomic force microscopy. A cleaning protocol was successfully applied to remove fungal hyphae without altering the underlying mineral structure and topography. Examination of the exposed chlorite surface showed the presence of primary channels, of the order of a micron in width and up to 50 nm in depth, the morphology of which strongly indicates a fungal-induced origin. Smaller secondary channels were observed extending from the primary channels and would appear to be involved in their enlargement. The presence of channels is the first nanoscale demonstration of the effects of fungal interaction, fuelled by plant photosynthate, on the topography of a chlorite mineral, and it provides clear evidence of the ability of EMF to enhance mineral dissolution

Technetium-99m transport and immobilisation in porous media: Development of a novel nuclear imaging technique

Technetium-99, a β-emitting radioactive fission product of U, formed in nuclear reactors, presents a major challenge to nuclear waste disposal strategies. Its long half-life (2.1 × 10 years) and high solubility under oxic conditions as the pertechnetate anion [Tc(VII)O] is particularly problematic for long-term disposal of radioactive waste in geological repositories. In this study, we demonstrate a novel technique for quantifying the transport and immobilisation of technetium-99m, a γ-emitting metastable isomer of technetium-99 commonly used in medical imaging. A standard medical gamma camera was used for non-invasive quantitative imaging of technetium-99m during co-advection through quartz sand and various cementitious materials commonly used in nuclear waste disposal strategies. Spatial moments analysis of the resulting Tc plume provided information about the relative changes in mass distribution of the radionuclide in the various test materials. Tc advected through quartz sand demonstrated typical conservative behaviour, while transport through the cementitious materials produced a significant reduction in radionuclide centre of mass transport velocity over time. Gamma camera imaging has proven an effective tool for helping to understand the factors which control the migration of radionuclides for surface, near-surface and deep geological disposal of nuclear waste. © 2013 Materials Research Society

The role of extracellular DNA in microbial attachment to oxidized silicon surfaces in the presence of Ca2+ and Na+

Attachment assays of a Pseudomonas isolate to fused silica slides showed that treatment with DNaseI significantly inhibited cellular adsorption, which was restored upon DNA treatment. These assays confirmed the important role of extracellular DNA (eDNA) adsorption to a surface. To investigate the eDNA adsorption mechanism, single-molecule force spectroscopy (SMFS) was used to measure the adsorption of eDNA to silicon surfaces in the presence of different concentrations of sodium and calcium ions. SMFS reveals that the work of adhesion required to remove calcium-bound eDNA from the silicon oxide surface is substantially greater than that for sodium. Molecular dynamics simulations were also performed, and here, it was shown that the energy gain in eDNA adsorption to a silicon oxide surface in the presence of calcium ions is small and much less than that in the presence of sodium. The simulations show that the length scales involved in eDNA adsorption are less in the presence of sodium ions than those in the presence of calcium. In the presence of calcium, eDNA is pushed above the surface cations, whereas in the presence of sodium ions, short-range interactions with the surface dominate. Moreover, SMFS data show that increasing [Ca2+] from 1 to 10 mM increases the adsorption of the cations to the silicon oxide surface and consequently enhances the Stern layer, which in turn increases the length scale associated with eDNA adsorption

Iron chelation in soil: scalable biotechnology for accelerating carbon dioxide removal by enhanced rock weathering

Enhanced rock weathering (EW) is an emerging atmospheric carbon dioxide removal (CDR) strategy being scaled up by the commercial sector. Here, we combine multiomics analyses of belowground microbiomes, laboratory-based dissolution studies, and incubation investigations of soils from field EW trials to build the case for manipulating iron chelators in soil to increase EW efficiency and lower costs. Microbial siderophores are high-affinity, highly selective iron (Fe) chelators that enhance the uptake of Fe from soil minerals into cells. Applying RNA-seq metatranscriptomics and shotgun metagenomics to soils and basalt grains from EW field trials revealed that microbial communities on basalt grains significantly upregulate siderophore biosynthesis gene expression relative to microbiomes of the surrounding soil. Separate in vitro laboratory incubation studies showed that micromolar solutions of siderophores and high-affinity synthetic chelator (ethylenediamine-N,N′-bis-2-hydroxyphenylacetic acid, EDDHA) accelerate EW to increase CDR rates. Building on these findings, we develop a potential biotechnology pathway for accelerating EW using the synthetic Fe-chelator EDDHA that is commonly used in agronomy to alleviate the Fe deficiency in high pH soils. Incubation of EW field trial soils with potassium-EDDHA solutions increased potential CDR rates by up to 2.5-fold by promoting the abiotic dissolution of basalt and upregulating microbial siderophore production to further accelerate weathering reactions. Moreover, EDDHA may alleviate potential Fe limitation of crops due to rising soil pH with EW over time. Initial cost-benefit analysis suggests potassium-EDDHA could lower EW-CDR costs by up to U.S. $77 t CO2 ha-1 to improve EW’s competitiveness relative to other CDR strategies

Soil Water Characteristics of European SoilTrEC Critical Zone Observatories

Most of soil functions depend directly or indirectly on soil water retention and transmission, which explains their importance for many environmental processes within Earth's Critical Zones. Soil hydraulic properties are essential in irrigation and drainage studies for closing water balance equation, for predicting leaching of nutrients, for water supply to plants, and for other agronomical and environmental applications. Soil hydraulic properties reflect the structure of the soil porous system comprising pores of different geometry and sizes. This investigation comprises a detailed analytical study of soil hydraulic properties and climate conditions at 18 methodologically selected sites in Damma Glacier, Slavkov Forest, Marchfeld, and Koiliaris Critical Zone Observatories of SoilTrEC project. The local moisture regimes were assessed on a long-term basis by the Newhall model. The experimental data for soil water content at different potentials were used for assessing water storage capacity, pore size distribution, parameters of fitted retention curve equation, curve slope at the inflection point, and water permeability characteristics of each soil horizon. The differences of soil water retention and transmission characteristics-as fundamental properties describing soil structure-were explained by the different stages of soil profile development, parent materials, organic matter content, and land use histories

Effects of mineralogy, chemistry and physical properties of basalts on carbon capture potential and plant-nutrient element release via enhanced weathering

Mafic igneous rocks, such as basalt, are composed of abundant calcium- and magnesium-rich silicate minerals widely proposed to be suitable for scalable carbon dioxide removal (CDR) by enhanced rock weathering (ERW). Here, we report a detailed characterization of the mineralogy, chemistry, particle size and surface area of six mined basalts being used in large-scale ERW field trials. We use 1-D reactive transport modelling (RTM) of soil profile processes to simulate inorganic CDR potential via cation flux (Mg2+, Ca2+, K+ and Na+) and assess the release of the essential plant nutrients phosphorus (P) and potassium (K) for a typical clay-loam agricultural soil. The basalts are primarily composed of pyroxene and plagioclase feldspar (up to 71 wt%), with accessory olivine, quartz, glass and alkali feldspar. Mean crushed particle size varies by a factor of 10, owing to differences in the mining operations and grinding processes. RTM simulations, based on measured mineral composition and N2-gas BET specific surface area (SSA), yielded potential CDR values of between c. 1.3 and 8.5 t CO2 ha−1 after 15 years following a baseline application of 50 t ha−1 basalt. The RTM results are comparative for the range of inputs that are described and should be considered illustrative for an agricultural soil. Nevertheless, they indicate that increasing the surface area for slow-weathering basalts through energy intensive grinding prior to field application in an ERW context may not be warranted in terms of additional CDR gains. We developed a function to convert CDR based on widely available and easily measured rock chemistry measures to more realistic determinations based on mineralogy. When applied to a chemistry dataset for >1300 basalt analyses from 25 large igneous provinces, we simulated cumulative CDR potentials of up to c. 8.5 t CO2 ha−1 after 30 years of weathering, assuming a single application of basalt with a SSA of 1 m2 g−1. Our RTM simulations suggest that ERW with basalt releases sufficient phosphorus (P) to substitute for typical arable crop P-fertiliser usage in Europe and the USA offering potential to reduce demand for expensive rock-derived P

Technologies to deliver food and climate security through agriculture

Agriculture is a major contributor to environmental degradation and climate change. At the same time, a growing human population with changing dietary preferences is driving ever increasing demand for food. The need for urgent reform of agriculture is widely recognized and has resulted in a number of ambitious plans. However, there is credible evidence to suggest that these are unlikely to meet the twin objectives of keeping the increase in global temperature within the target of 2.0 °C above preindustrial levels set out in the Paris Agreement and delivering global food security. Here, we discuss a series of technological options to bring about change in agriculture for delivering food security and providing multiple routes to the removal of CO2 from the atmosphere. These technologies include the use of silicate amendment of soils to sequester atmospheric CO2, agronomy technologies to increase soil organic carbon, and high-yielding resource-efficient crops to deliver increased agricultural yield, thus freeing land that is less suited for intensive cropping for land use practices that will further increase carbon storage. Such alternatives include less intensive regenerative agriculture, afforestation and bioenergy crops coupled with carbon capture and storage technologies

Modeling the dynamics of fermentation and respiratory processes in a groundwater plume of phenolic contaminants interpreted from laboratory-to field-scale

A biodegradation model with consecutive fermentation and respiration processes, developed from microcosm experiments and simulated mathematically with microbial growth kinetics, has been implemented into a field-scale reactive transport model of a groundwater plume of phenolic contaminants. Simulation of the anaerobic plume core with H2 and acetate as intermediate products of biodegradation allows the rates and parameter values for fermentation processes and individual respiratory terminal electron accepting processes (TEAPS) to be estimated using detailed, spatially discrete, hydrochemical field data. The modeling of field-scale plume development includes consideration of microbial acclimatization, substrate toxicity toward degradation, bioavailability of mineral oxides, and adsorption of biogenic Fe(II) species in the aquifer, identified from complementary laboratory process studies. The results suggest that plume core processes, particularly fermentation and Fe(III)-reduction, are more important for degradation than previously thought, possibly with a greater impact than plume fringe processes (aerobic respiration, denitrification, and SO4-reduction). The accumulation of acetate as a fermentation product within the plume contributes significantly to the mass balance for carbon. These results demonstrate the value of quantifying fermentation products within organic contaminant plumes and strongly suggest that the conceptual model selected for reactive processes plays a dominant role in the quantitative assessment of risk reduction by naturally occurring biodegradation processes