Unveiling the Pool of Metallophores in Native Environments and Correlation with Their Potential Producers.

For many organisms, metallophores are essential biogenic ligands that ensure metal scavenging and acquisition from their environment. Their identification is challenging in highly organic matter rich environments like peatlands due to low solubilization and metal scarcity and high matrix complexity. In contrast to common approaches based on sample modification by spiking of metal isotope tags, we have developed a two-dimensional (2D) Solid-phase extraction-Liquid chromatography-mass spectrometry (SPE-LC-MS) approach for the highly sensitive (LOD 40 fmol per g of soil), high-resolution direct detection and identification of metallophores in both their noncomplexed (apo) and metal-complexed forms in native environments. The characterization of peat collected in the Bernadouze (France) peatland resulted in the identification of 53 metallophores by a database mass-based search, 36 among which are bacterial. Furthermore, the detection of the characteristic (natural) metal isotope patterns in MS resulted in the detection of both Fe and Cu potential complexes. A taxonomic-based inference method was implemented based on literature and public database (antiSMASH database version 3.0) searches, enabling to associate over 40% of the identified bacterial metallophores with potential producers. In some cases, low completeness with the MIBiG reference BCG might be indicative of alternative producers in the ecosystem. Thus, coupling of metallophore detection and producers' inference could pave a new way to investigate poorly documented environment searching for new metallophores and their producers yet unknown.

Quantitative Determination of Iron-Siderophore Complexes in Peat by Isotope-Exchange Size-Exclusion UPLC-Electrospray Ionization High-Resolution Accurate Mass (HRAM) Mass Spectrometry.

A method was developed for the quantification of iron-siderophore complexes by electrospray high-resolution accurate mass (HRAM) mass spectrometry (MS) without the need for authentic standards. The bulk of iron-siderophore complexes was purified by solid-phase extraction (SPE) and concentrated by evaporation. The individual complexes were identified by fast size-exclusion chromatography (FastSEC)-Orbitrap MSn on the basis of the exact molecular mass (±1 ppm) and MS2 or MS3 fragmentation. Their capability to readily exchange the natural 56Fe for the added 58Fe was demonstrated by SEC with ICP MS and ESI MS detection. The method was applied to the analysis of peat sampled in the eastern part of the French Pyrenean mountains. Nineteen siderophores belonging to four different classes were identified and quantified. The results were validated using ICP MS detection of iron by matching the sum of iron complexes determined by isotope exchange-ESI MS within each peak observed by FastSEC-ICP MS.

Upside down sulphate dynamics in a saline inland lake.

The sulphur cycle has a key role on the fate of nutrients through its several interconnected reactions. Although sulphur cycling in aquatic ecosystems has been thoroughly studied since the early 70's, its characterisation in saline endorheic lakes still deserves further exploration. Gallocanta Lake (NE Spain) is an ephemeral saline inland lake whose main sulphate source is found on the lake bed minerals and leads to dissolved sulphate concentrations higher than those of seawater. An integrative study including geochemical and isotopic characterization of surface water, porewater and sediment has been performed to address how sulphur cycling is constrained by the geological background. In freshwater and marine environments, sulphate concentration decreases with depth are commonly associated with bacterial sulphate reduction (BSR). However, in Gallocanta Lake sulphate concentrations in porewater increase from 60 mM at the water-sediment interface to 230 mM at 25 cm depth. This extreme increase could be caused by dissolution of the sulphate rich mineral epsomite (MgSO4·7H2O). Sulphur isotopic data was used to validate this hypothesis and demonstrate the occurrence of BSR near the water-sediment interface. This dynamic prevents methane production and release from the anoxic sediment, which is advantageous in the current context of global warming. These results underline that geological context should be considered in future biogeochemical studies of inland lakes with higher potential availability of electron acceptors in the lake bed compared to the water column.