Bioweathering of nontronite colloids in hybrid silica gel: implications for iron mobilization

Abstract

Aims: This study aimed to study biotic iron dissolution using a new hybrid material constituted of well-dispersed mineral colloids in a silica gel matrix. This permitted to prevent adsorption of colloidal mineral particles on bacteria. Hybrid silica gel (HSG) permitted to study bioweathering mechanisms by diffusing molecules. Methods and Results: Hybrid silica gel was synthesized through a classical sol-gel procedure in which mineral colloidal particles (NAu-2) were embedded in a porous silica matrix. Rahnella aquatilis RA1, isolated from a wheat rhizosphere was chosen for its ability to dissolve minerals by producing various organic acids and siderophores. Pyruvic, acetic and lactic acids were the major organic acids produced by R. aquatilis RA1 followed by oxalic and citric acids at the end of incubation. Comparison of abiotic and biotic experiments revealed a high efficiency of R. aquatilis RA1 for iron dissolution suggesting an optimized action of different ligands that solubilized or mobilized iron. Conclusions: Hybrid silica gel allowed focusing on the colloidal mineral weathering by metabolites diffusion without mineral adsorption on bacteria. Significance and Impact of the Study: Hybrid silica gels are new and efficient tools to study colloidal mineral bioweathering. Adjusting HSG porosity and hydrophobicity should permit to precise the influence of limiting diffusion of siderophores or aliphatic organic acids on mineral weathering.

Bioavailability of Colloidal Iron to Heterotrophic Bacteria in Sediments, and Effects on the Mobility of Colloid-Associated Metal(loid)s

“…In the natural environment under aerobic conditions, Fe is commonly present in the form of Fe(oxy)hydroxides or is associated with organic compounds. Numerous studies have shown that bacteria employ various strategies to acquire mineral nutrients such as acidification, the synthesis of siderophores and organic acids, or the colonization of mineral surfaces [50][51][52][53]. As expected, nutrient uptake by bacteria involved the release of Fe into the solution, demonstrating the implication of microbial metabolites in the solubilization of colloidal Fe phases.…”

Biogenic Weathering: Solubilization of Iron from Minerals by Epilithic Freshwater Algae and Cyanobacteria

“…Bacteria and fungi produce a diverse variety of catecholate and hydroxamate siderophores [ 40 , 41 , 42 ]. In algae and higher plants, carboxylic acid siderophores predominate [ 43 ].…”

Interactions of three soil bacteria species with phyllosilicate surfaces in hybrid silica gels

“…As Fe can precipitate and/or adsorb onto the silica and mineral surfaces, one volume HSG was treated with two volumes of potassium chloride and hydroxylamine (KCl 1 M; NH 2 OH 0.2%) to extract amorphous Fe at the end of each experiment After 1 h at 28°C, amorphous Fe extracted from HSG with potassium chloride and hydroxylamine solution and soluble Fe in weathering solutions were quantified by absorbance measurement at 565 nm after addition of 20 lL of Ferrospectral â dye indicator to 200 lL of filtered solutions (Balland et al, 2010;Grybos et al, 2010;Oulkadi et al, 2014). The detection limit was found as low as 20 lg L À1 under our conditions.…”

“…Each liter of salt solution was supplemented with sterilized filtered solutions of 10% (w/v) Chelex 100-treated Casamino acids (Difco Laboratories) 20 mL, MgSO 4 (1 M) 2 mL, 20% (w/v) glucose 10 mL, and CaCl 2 (1 M) 0.1 mL (Kalinowski et al, 2000). Siderophore concentration was determined at 630 nm according to a calibration curve made with desferrioxamine mesylate (DFOM; Sigma-Aldrich; Payne, 1994;Oulkadi et al, 2014).…”

“…Hybrid silica gels (HSGs) were produced according to a conventional sol‐gel pathway (Grybos et al ., ). HSG provided mineral particles embedded in highly hydrated silica matrix where only diffusing small molecules, that is, LMWOA and siderophores, were able to penetrate and alter clay minerals (Oulkadi et al ., ). Pore diameter of wet silica gels was less than 10 nm, whereas bacterial cells are about 1–2 μm length (Dickson & Ely, ).…”