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1. Sulfide oxidation by members of the Sulfolobales

   https://doi.org/10.1093/pnasnexus/pgae201  

   Fernandes-Martins, Maria C; Colman, Daniel R; Boyd, Eric S (May 2024, PNAS Nexus)

   Fukami, Tadashi (Ed.)

   The oxidation of sulfur compounds drives the acidification of geothermal waters. At high temperatures (>80°C) and in acidic conditions (pH <6.0), oxidation of sulfide has historically been considered an abiotic process that generates elemental sulfur (S0) that, in turn, is oxidized by thermoacidophiles of the model archaeal order Sulfolobales to generate sulfuric acid (i.e. sulfate and protons). Here, we describe five new aerobic and autotrophic strains of Sulfolobales comprising two species that were isolated from acidic hot springs in Yellowstone National Park (YNP) and that can use sulfide as an electron donor. These strains significantly accelerated the rate and extent of sulfide oxidation to sulfate relative to abiotic controls, concomitant with production of cells. Yields of sulfide-grown cultures were ∼2-fold greater than those of S0-grown cultures, consistent with thermodynamic calculations indicating more available energy in the former condition than the latter. Homologs of sulfide:quinone oxidoreductase (Sqr) were identified in nearly all Sulfolobales genomes from YNP metagenomes as well as those from other reference Sulfolobales, suggesting a widespread ability to accelerate sulfide oxidation. These observations expand the role of Sulfolobales in the oxidative sulfur cycle, the geobiological feedbacks that drive the formation of acidic hot springs, and landscape evolution. 

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2. Subsurface Archaea associated with rapid geobiological change in a model Yellowstone hot spring

   https://doi.org/10.1038/s43247-022-00542-2  

   Colman, Daniel_R; Amenabar, Maximiliano_J; Fernandes-Martins, Maria_C; Boyd, Eric_S (September 2022, Communications Earth & Environment)

   Abstract Despite over a century of study, it is unknown if continental hydrothermal fields support high-temperature subsurface biospheres. Cinder Pool is among the deepest hot springs in Yellowstone and is widely studied due to unique sulfur geochemistry that is attributed to hydrolysis of molten elemental sulfur at ∼18 m depth that promotes several chemical reactions that maintain low sulfide, low oxygen, and a moderate pH of ∼4.0. Following ∼100 years of stability, Cinder Pool underwent extreme visual and chemical change (acidification) in 2018. Here, we show that depth-resolved geochemical and metagenomic-based microbial community analyses pre- (2016) and post-acidification (2020) indicate the changes are likely attributable to feedbacks between geological/geochemical processes, sulfur oxidation by subsurface Sulfolobales Archaea, and the disappearance of molten sulfur at depth. These findings underscore the dynamic and rapid feedback between the geosphere and biosphere in continental hydrothermal fields and suggest subsurface biospheres to be more prevalent in these systems than previously recognized. 

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3. Uncovering and quantifying the subduction zone sulfur cycle from the slab perspective

   https://doi.org/10.1038/s41467-019-14110-4  

   Li, Ji-Lei; Schwarzenbach, Esther_M; John, Timm; Ague, Jay_J; Huang, Fang; Gao, Jun; Klemd, Reiner; Whitehouse, Martin_J; Wang, Xin-Shui (January 2020, Nature Communications)

   Abstract Sulfur belongs among H₂O, CO₂, and Cl as one of the key volatiles in Earth’s chemical cycles. High oxygen fugacity, sulfur concentration, and δ³⁴S values in volcanic arc rocks have been attributed to significant sulfate addition by slab fluids. However, sulfur speciation, flux, and isotope composition in slab-dehydrated fluids remain unclear. Here, we use high-pressure rocks and enclosed veins to provide direct constraints on subduction zone sulfur recycling for a typical oceanic lithosphere. Textural and thermodynamic evidence indicates the predominance of reduced sulfur species in slab fluids; those derived from metasediments, altered oceanic crust, and serpentinite have δ³⁴S values of approximately −8‰, −1‰, and +8‰, respectively. Mass-balance calculations demonstrate that 6.4% (up to 20% maximum) of total subducted sulfur is released between 30–230 km depth, and the predominant sulfur loss takes place at 70–100 km with a net δ³⁴S composition of −2.5 ± 3‰. We conclude that modest slab-to-wedge sulfur transport occurs, but that slab-derived fluids provide negligible sulfate to oxidize the sub-arc mantle and cannot deliver³⁴S-enriched sulfur to produce the positive δ³⁴S signature in arc settings. Most sulfur has negative δ³⁴S and is subducted into the deep mantle, which could cause a long-term increase in the δ³⁴S of Earth surface reservoirs. 

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4. Single‐Step Sulfur Insertions into Iron Carbide Carbonyl Clusters: Unlocking the Synthetic Door to FeMoco Analogues

   https://doi.org/10.1002/ange.202011517  

   Joseph, Chris; Cobb, Caitlyn R.; Rose, Michael J. (December 2020, Angewandte Chemie)

   Abstract The one‐step syntheses, X‐ray structures, and spectroscopic characterization of synthetic iron clusters, bearing either inorganic sulfides or thiolate with interstitial carbide motifs, are reported. Treatment of iron carbide carbonyl clusters [Fe_n(μ_n‐C)(CO)_m]^x(n=5,6;m=15,16;x=0,−2) with electrophilic sulfur sources (S₂Cl₂, S₈) results in the formation of several μ₄‐S dimers of clusters, and moreover, iron‐sulfide‐(sulfocarbide) clusters. The core sulfocarbide unit {C−S}⁴⁻serves as a structural model for a proposed intermediate in the radicalS‐adenosyl‐L‐methionine biogenesis of the M‐cluster. Furthermore, the electrophilic sulfur strategy has been extended to provide the first ever thiolato‐iron‐carbide complex: an analogous reaction with toluylsulfenyl chloride affords the cluster [Fe₅(μ₅‐C)(SC₇H₇)(CO)₁₃]⁻. The strategy described herein provides a breakthrough towards developing syntheses of biomimetic iron‐sulfur‐carbide clusters like FeMoco. 

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5. Ligand Basicity and Chelate Effects on Sulfur Insertion vs. Sulfur Reduction by Zinc Thiolate Complexes

   https://doi.org/10.1002/chem.202401280  

   Seo, W_T_Michael; Tsang, Victor_A; Ballesteros, II, Moises; Tsui, Emily_Y (June 2024, Chemistry – A European Journal)

   Abstract 4‐ and 5‐coordinate zinc thiolate complexes supported either by bis(carboxamide)pyridine frameworks or by substituted tris(pyrazolyl)borate ligands react with elemental sulfur (S₈) following two distinct pathways. Some zinc thiolate moieties insert sulfur atoms to form zinc polysulfanide complexes, while others reduce sulfur and oxidize the thiolate. Here, we compare the effects of ligand electronics, strain, and sterics for selecting the respective reaction pathway. These results show that chelating and electron‐deficient thiolate ligands better stabilize persistent zinc‐bound polysulfanide species. 

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