Protohistoric briquetage at Puntone (Tuscany, Italy) : principles and processes of an industry based on the leaching of saline lagoonal sediments

A protohistoric (c.10th–5th c. BC) briquetage site at Puntone (Tuscany, Italy) was studied to unravel the salt production processes and materials involved. Geophysical surveys were used to identify kilns, pits, and dumps. One of these pits and a dump were excavated, followed by detailed chemical and physical analyses of the materials encountered. The pit had been used for holding brine, obtained by leaching of lagoonal sediment over a sieve, that afterwards was discarded to form large dumps. Phases distinguished indicate that the pit filled with fine sediment and was regularly “cleaned.” The presence of ferroan‐magnesian calcite in the pit fill testifies to the prolonged presence of anoxic brine. The production processes could be reconstructed in detail by confronting the analytical results with known changes in composition of a brine upon evaporation. These pertain in particular to the accumulation of “bitterns” and increased B (boron) concentrations in a residual brine. Both could be traced in the materials studied, and were found to be far more indicative than the ubiquitously studied concentrations of Cl and Na

The protohistoric briquetage at Puntone (Tuscany, Italy):A multidisciplinary attempt to unravel its age and role in the salt supply of Early States in Tyrrhenian Central Italy

While processes involved in the protohistoric briquetage at Puntone (Tuscany, Italy) have been reconstructed in detail, the age of this industry remained uncertain since materials suited for traditional dating (14C dating on charcoal and typological dating of ceramics) were very scarce. We attempted to assess its age by radiocarbon dating organic matter and carbonates in strata that were directly linked to the industry. Microbial DNA and C isotope analyses showed that the organic matter is dominantly composed of labile organic matter, of which the age is coeval with the briquetage industry. Carbonates had a complex origin and were overall unsuited for radiocarbon dating: Shells in process residues exhibited a large, uncertain ‘marine reservoir effect’, hampering their use for dating the industry; the secondary carbonates in these residues had a quite varied composition, including much more recent carbonate that precipitated from infiltrated lateral run-off, as could be concluded from C and Sr isotope analyses. Dates found that were deemed reliable (c. 1000–100 cal BCE) show that this ancient industry, which started in the Late Bronze Age - Early Iron Age (1107–841 cal BCE), extended into the Roman Republican period and was contemporary with the saltern-based larger scale salt industry in Central Lazio

Life at the extreme: Plant-driven hotspots of soil nutrient cycling in the hyper-arid core of the Atacama Desert

The hyperarid core of the Atacama Desert represents one of the most intense environments on Earth, often being used as an analog for Mars regolith. The area is characterized by extremes in climate (e.g., temperature, humidity, UV irradiation) and edaphic factors (e.g., hyper-salinity, high pH, compaction, high perchlorates, and low moisture, phosphorus and organic matter). However, the halophytic C4 plant Distichlis spicata appears to be one of the few species on the planet that can thrive in this environment. Within this habitat it captures windblown sand leading to the formation of unique structures and the generation of above-ground phyllosphere soil. Using a combination of approaches (e.g., X-ray Computed Tomography, TXRF, δ13C/δ15N isotope profiling, microbial PLFAs, 14C turnover, phosphate sorption isotherms) we examined the factors regulating the biogeochemical cycling of nitrogen (N), phosphorus (P) and carbon (C) in both vegetated and unvegetated areas. Our results showed that D. spicata rhizomes with large aerenchyma were able to break through the highly cemented topsoil layer leading to root proliferation in the underlying soil. The presence of roots increased soil water content, P availability and induced a change in microbial community structure and promoted microbial growth and activity. In contrast, soil in the phyllosphere exhibited almost no biological activity. Organic C stocks and recent C4 plant derived input increased as follows: phyllosphere (1941 g C m−2; 85% recent) > soils under plants (575–748 g C m−2; 55–60%) > bare soils (491–642 g C m−2; 9–17%). Due to the high levels of nitrate in soil (>2 t ha−1) and high rates of P sorption/precipitation, our data suggest that the microbial activity is both C and P, but not N limited. Root-mediated salt uptake combined with foliar excretion and dispersal of NaCl into the surrounding area indicated that D. spicata was responsible for actively removing ca. 55% of the salt from the rhizosphere. We also demonstrate that NH3 emissions may represent a major N loss pathway from these soil ecosystems during the processing of organic N. We attribute this to NH3 volatilization to the high pH of the soil and slow rates of nitrification. In conclusion, we demonstrate that the extremophile D. spicata physically, chemically and biologically reengineers the soil to create a highly bioactive hotspot within the climate-extreme of the Atacama Desert

Metagenomes and metatranscriptomes shed new light on the microbial-mediated sulfur cycle in a Siberian soda lake

Background: The planetary sulfur cycle is a complex web of chemical reactions that can be microbial-mediated or can occur spontaneously in the environment, depending on the temperature and pH. Inorganic sulfur compounds can serve as energy sources for specialized prokaryotes and are important substrates for microbial growth in general. Here, we investigate dissimilatory sulfur cycling in the brine and sediments of a southwestern Siberian soda lake characterized by an extremely high pH and salinity, combining meta-omics analyses of its uniquely adapted highly diverse prokaryote communities with biogeochemical profiling to identify key microbial players and expand our understanding of sulfur cycling under haloalkaline conditions. Results: Peak microbial activity was found in the top 4 cm of the sediments, a layer with a steep drop in oxygen concentration and redox potential. The majority of sulfur was present as sulfate or iron sulfide. Thiosulfate was readily oxidized by microbes in the presence of oxygen, but oxidation was partially inhibited by light. We obtained 1032 metagenome-assembled genomes, including novel population genomes of characterized colorless sulfur-oxidizing bacteria (SOB), anoxygenic purple sulfur bacteria, heterotrophic SOB, and highly active lithoautotrophic sulfate reducers. Surprisingly, we discovered the potential for nitrogen fixation in a new genus of colorless SOB, carbon fixation in a new species of phototrophic Gemmatimonadetes, and elemental sulfur/sulfite reduction in the "Candidatus Woesearchaeota." Polysulfide/thiosulfate and tetrathionate reductases were actively transcribed by various (facultative) anaerobes. Conclusions: The recovery of over 200 genomes that encoded enzymes capable of catalyzing key reactions in the inorganic sulfur cycle indicates complete cycling between sulfate and sulfide at moderately hypersaline and extreme alkaline conditions. Our results suggest that more taxonomic groups are involved in sulfur dissimilation than previously assumed.</p

Quantum catalysis: The modeling of catalytic transition states

We present an introduction to the computational modeling of transition states for catalytic reactions. We consider both homogeneous catalysis and heterogeneous catalysis, including organometallic catalysts, enzymes, zeolites and metal oxides, and metal surfaces. We summarize successes, promising approaches, and problems. We attempt to delineate the key issues and summarize the current status of our understanding of these issues. Topics covered include basis sets, classical trajectories, cluster calculations, combined quantum-mechanical/molecular-mechanical (QM/MM) methods, density functional theory, electrostatics, empirical valence bond theory, free energies of activation, frictional effects and nonequilibrium solvation, kinetic isotope effects, localized orbitals at surfaces, the reliability of correlated electronic structure calculations, the role of d orbitals in transition metals, transition state geometries, and tunneling

Metagenomes and metatranscriptomes shed new light on the microbial-mediated sulfur cycle in a Siberian soda lake

Background: The planetary sulfur cycle is a complex web of chemical reactions that can be microbial-mediated or can occur spontaneously in the environment, depending on the temperature and pH. Inorganic sulfur compounds can serve as energy sources for specialized prokaryotes and are important substrates for microbial growth in general. Here, we investigate dissimilatory sulfur cycling in the brine and sediments of a southwestern Siberian soda lake characterized by an extremely high pH and salinity, combining meta-omics analyses of its uniquely adapted highly diverse prokaryote communities with biogeochemical profiling to identify key microbial players and expand our understanding of sulfur cycling under haloalkaline conditions. Results: Peak microbial activity was found in the top 4 cm of the sediments, a layer with a steep drop in oxygen concentration and redox potential. The majority of sulfur was present as sulfate or iron sulfide. Thiosulfate was readily oxidized by microbes in the presence of oxygen, but oxidation was partially inhibited by light. We obtained 1032 metagenome-assembled genomes, including novel population genomes of characterized colorless sulfur-oxidizing bacteria (SOB), anoxygenic purple sulfur bacteria, heterotrophic SOB, and highly active lithoautotrophic sulfate reducers. Surprisingly, we discovered the potential for nitrogen fixation in a new genus of colorless SOB, carbon fixation in a new species of phototrophic Gemmatimonadetes, and elemental sulfur/sulfite reduction in the "Candidatus Woesearchaeota." Polysulfide/thiosulfate and tetrathionate reductases were actively transcribed by various (facultative) anaerobes. Conclusions: The recovery of over 200 genomes that encoded enzymes capable of catalyzing key reactions in the inorganic sulfur cycle indicates complete cycling between sulfate and sulfide at moderately hypersaline and extreme alkaline conditions. Our results suggest that more taxonomic groups are involved in sulfur dissimilation than previously assumed.BT/Environmental Biotechnolog

Quantum catalysis: The modeling of catalytic transition states

We present an introduction to the computational modeling of transition states for catalytic reactions. We consider both homogeneous catalysis and heterogeneous catalysis, including organometallic catalysts, enzymes, zeolites and metal oxides, and metal surfaces. We summarize successes, promising approaches, and problems. We attempt to delineate the key issues and summarize the current status of our understanding of these issues. Topics covered include basis sets, classical trajectories, cluster calculations, combined quantum-mechanical/molecular-mechanical (QM/MM) methods, density functional theory, electrostatics, empirical valence bond theory, free energies of activation, frictional effects and nonequilibrium solvation, kinetic isotope effects, localized orbitals at surfaces, the reliability of correlated electronic structure calculations, the role of d orbitals in transition metals, transition state geometries, and tunneling