In situ Lithium and Boron isotope determinations in mica, pyroxene, and serpentine by LA-MC-ICP-MS

Boron and Li are light, incompatible elements that preferentially partition into the liquid phase, whether melt or aqueous fluid, and thus are useful for tracking fluid-related processes in rocks. Most of the Li isotopic data presently available on subduction-related rocks are from whole-rock analyses; and the B isotopic analyses of subduction material have been carried out either on whole-rocks or in-situ on an accessory phase, such as tourmaline. The new method presented here couples an ESI New Wave UP-193-FX ArF* (193 nm) excimer laser-ablation microscope with a Neptune Plus (Thermo Scientific) MC-ICP-MS aiming to measure both Li and B isotopes in situ with good spatial resolution (metamorphic minerals are commonly chemically zoned, and whole-rock analyses lose this detail). The data thus obtained are compared with SIMS analyses on the same mineral samples for B, and with MC-ICP-MS analyses on whole-rock or mineral separates from the same sample for Li. Additionally, data acquired on tourmaline standards were compared to SIMS values. The results show that for B concentrations above 5 μg/g, the data obtained by LA-MC-ICP-MS and by SIMS are identical within error, for mica (phengitic muscovite), pyroxene (jadeite), serpentine (antigorite), and tourmaline. For Li concentrations above 10 μg/g, the data obtained by LA-MC-ICP-MS and by MC-ICP-MS are also identical, within error, for mica (phengitic muscovite), and pyroxene (jadeite). However, analyses of tourmaline standards have shown significant differences with reference values, so LA-MC-ICP-MS does not yet appear to be an appropriate method to analyze Li isotopes in tourmalines. Thus, LA-MC-ICP-MS is a suitable method to measure Li and B isotopes with good spatial resolution in major rock-forming silicates from subduction-related rocks where concentrations exceed 10 μg/g and 5 μg/g, respectively, with an error on individual measurements equal to or less than previously used methods, but obtainable in a significantly shorter amount of time. The external reproducibility is ± 2.88 to 3.31 ‰ for B and ± 1.50 to 1.75 for Li, which is lower than or equal to the variations encountered within a given chemically zoned sample (up to 10 ‰ of variation within a given natural sample).

Deconjugated Bile Salts Produced by Extracellular Bile-Salt Hydrolase-Like Activities from the Probiotic Lactobacillus johnsonii La1 Inhibit Giardia duodenalis In vitro Growth

Giardiasis, currently considered a neglected disease, is caused by the intestinal protozoan parasite Giardia duodenalis and is widely spread in human as well as domestic and wild animals. The lack of appropriate medications and the spread of resistant parasite strains urgently call for the development of novel therapeutic strategies. Host microbiota or certain probiotic strains have the capacity to provide some protection against giardiasis. By combining biological and biochemical approaches, we have been able to decipher a molecular mechanism used by the probiotic strain Lactobacillus johnsonii La1 to prevent Giardia growth in vitro. We provide evidence that the supernatant of this strain contains active principle(s) not directly toxic to Giardia but able to convert non-toxic components of bile into components highly toxic to Giardia. By using bile acid profiling, these components were identified as deconjugated bile-salts. A bacterial bile-salt-hydrolase of commercial origin was able to mimic the properties of the supernatant. Mass spectrometric analysis of the bacterial supernatant identified two of the three bile-salt-hydrolases encoded in the genome of this probiotic strain. These observations document a possible mechanism by which L. johnsonii La1, by secreting, or releasing BSH-like activity(ies) in the vicinity of replicating Giardia in an environment where bile is present and abundant, can fight this parasite. This discovery has both fundamental and applied outcomes to fight giardiasis, based on local delivery of deconjugated bile salts, enzyme deconjugation of bile components, or natural or recombinant probiotic strains that secrete or release such deconjugating activities in a compartment where both bile salts and Giardia are present.