Meta-omics survey of [NiFe]-hydrogenase genes fails to capture drastic variations in H2-oxidation activity measured in three soils exposed to H2

Inferences on soil biogeochemical processes based on metagenomic profiles is a challenging task due to enormous diversity of soil microbes and the fragile linkage between gene abundance and functioning. Here we used the biological sink of H2 as a case study to test the hypothesis that [NiFe]-hydrogenase gene distribution and expression profiles explain variations in H2 oxidation rate measured in soil collected in poplar monoculture, larch plantation and farmland. Shotgun metagenomic and metatranscriptomic analyses of soil samples exposed to elevated or low H2 concentration led to the identification of 45 genes encoding the large subunit of [NiFe]-hydrogenases belonging to 8 distinct phyla. Our results indicate that despite significant sequencing effort, retrieved hydrogenase sequences are not in themselves adequate surrogates of H2 oxidation activity in these soils. In fact, land-use exerted a greater influence than H2 exposure on both hydrogenase gene distribution and expression though expression of certain genes responded to H2. We argue that approaches relying on PCR/RT-PCR amplicon sequencing or quantification combined with physicochemical parameters are currently the best option to infer the activity of H2-oxidizing bacteria and probably other specialist functional guilds with similar population size in soil

Encapsulation of (E)-N’-(1-(7-(diethylamino)-2-oxo-2H-chromen-3 yl)ethylidene)benzohydrazide (7-diEAHC) in β-cyclodextrins: Optimized synthesis of 7-diEACH and in silico ADME profiling, physical stability, antioxidant properties of encapsulated 7-diEAHC and bioavailability in rats

International audienceThe β-cyclodextrins (β-CD) as supramolecular have extremely attractive pharmaceutical applications. This study focused on the effects of macrocyclic systems complexation on stability, antioxidant activities, and bioavailability of the optimized synthesis coumarin incorporating hydrazone moiety. Optimal synthesis of (E)-N’-(1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)ethylidene)benzohydrazide (7-diEAHC) was performed by using response surface methodology (RSM) with a temperature of 100 °C, a reaction time of 10 min in the presence of acetic acid (0.85 M). Physicochemical properties and in silico ADME profiling of 7-diEAHC were also determined. The encapsulation efficiencies of the 7-diEAHC were above 81 % for the micro-encapsulates. After sunlight exposure, the 7-diEAHC-β-CD inclusion complex showed a photostability 19.4 % higher than free 7-diEAHC. Additionally, the encapsulated 7-diEAHC exhibited better stability than free 7-diEAHC for the pH varied between 1 and 9. From the results, storage stability showed that the encapsulation method using β-CD conferred a greater ability of 7-diEAHC against temperature. The NMR and FT-IR techniques were employed to evaluate the chemical stability of 7-diEAHC after encapsulation. In addition, in vivo study showed that the micro-encapsulation approach increased the oral bioavailability of 7-diEAHC in treated rats. © 202

Trace gas oxidizers are widespread and active members of soil microbial communities

International audienceSoil microorganisms globally are thought to be sustained primarily by organic carbon sources. Certain bacteria also consume inorganic energy sources such as trace gases, but they are presumed to be rare community members, except within some oligotrophic soils. Here we combined metagenomic, biogeochemical and modelling approaches to determine how soil microbial communities meet energy and carbon needs. Analysis of 40 metagenomes and 757 derived genomes indicated that over 70% of soil bacterial taxa encode enzymes to consume inorganic energy sources. Bacteria from 19 phyla encoded enzymes to use the trace gases hydrogen and carbon monoxide as supplemental electron donors for aerobic respiration. In addition, we identified a fourth phylum (Gemmatimonadota) potentially capable of aerobic methanotrophy. Consistent with the metagenomic profiling, communities within soil profiles from diverse habitats rapidly oxidized hydrogen, carbon monoxide and to a lesser extent methane below atmospheric concentrations. Thermodynamic modelling indicated that the power generated by oxidation of these three gases is sufficient to meet the maintenance needs of the bacterial cells capable of consuming them. Diverse bacteria also encode enzymes to use trace gases as electron donors to support carbon fixation. Altogether, these findings indicate that trace gas oxidation confers a major selective advantage in soil ecosystems, where availability of preferred organic substrates limits microbial growth. The observation that inorganic energy sources may sustain most soil bacteria also has broad implications for understanding atmospheric chemistry and microbial biodiversity in a changing world

A widely distributed hydrogenase oxidises atmospheric H2 during bacterial growth

Diverse aerobic bacteria persist by consuming atmospheric hydrogen (H) using group 1h [NiFe]-hydrogenases. However, other hydrogenase classes are also distributed in aerobes, including the group 2a [NiFe]-hydrogenase. Based on studies focused on Cyanobacteria, the reported physiological role of the group 2a [NiFe]-hydrogenase is to recycle H produced by nitrogenase. However, given this hydrogenase is also present in various heterotrophs and lithoautotrophs lacking nitrogenases, it may play a wider role in bacterial metabolism. Here we investigated the role of this enzyme in three species from different phylogenetic lineages and ecological niches: Acidithiobacillus ferrooxidans (phylum Proteobacteria), Chloroflexus aggregans (phylum Chloroflexota), and Gemmatimonas aurantiaca (phylum Gemmatimonadota). qRT-PCR analysis revealed that the group 2a [NiFe]-hydrogenase of all three species is significantly upregulated during exponential growth compared to stationary phase, in contrast to the profile of the persistence-linked group 1h [NiFe]-hydrogenase. Whole-cell biochemical assays confirmed that all three strains aerobically respire H to sub-atmospheric levels, and oxidation rates were much higher during growth. Moreover, the oxidation of H supported mixotrophic growth of the carbon-fixing strains C. aggregans and A. ferrooxidans. Finally, we used phylogenomic analyses to show that this hydrogenase is widely distributed and is encoded by 13 bacterial phyla. These findings challenge the current persistence-centric model of the physiological role of atmospheric H oxidation and extend this process to two more phyla, Proteobacteria and Gemmatimonadota. In turn, these findings have broader relevance for understanding how bacteria conserve energy in different environments and control the biogeochemical cycling of atmospheric trace gases