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Trace metals have been an important ingredient for life throughout Earth’s history. Here, we describe the genome-guided cultivation of a member of the elusive archaeal lineage Caldarchaeales (syn. Aigarchaeota), Wolframiiraptor gerlachensis, and its growth dependence on tungsten. A metagenome-assembled genome (MAG) of W. gerlachensis encodes putative tungsten membrane transport systems, as well as pathways for anaerobic oxidation of sugars probably mediated by tungsten-dependent ferredoxin oxidoreductases that are expressed during growth. Catalyzed reporter deposition-fluorescence in-situ hybridization (CARD-FISH) and nanoscale secondary ion mass spectrometry (nanoSIMS) show that W. gerlachensis preferentially assimilates xylose. Phylogenetic analyses of 78 high-quality Wolframiiraptoraceae MAGs from terrestrial and marine hydrothermal systems suggest that tungsten-associated enzymes were present in the last common ancestor of extant Wolframiiraptoraceae. Our observations imply a crucial role for tungsten-dependent metabolism in the origin and evolution of this lineage, and hint at a relic metabolic dependence on this trace metal in early anaerobic thermophiles.

The rates of microbial and abiotic iron oxidation were determined in a variety of cold (T = 9–12 °C), circumneutral (pH = 5.5–9.0) environments in the Swiss Alps. These habitats include iron–bicarbonate springs, iron–arsenic–bicarbonate springs, and alpine lakes. Rates of microbial iron oxidation were measured up to a pH of 7.4, with only abiotic processes detected at higher pH values. Iron oxidizing bacteria (FeOB) were responsible for 39–89% of the net oxidation rate at locations where biological iron oxidation was detected. Members of putative iron oxidizing genera, especially Gallionella, are abundant in systems where biological iron oxidation was measured. Geochemical sampling suites accompanying each experiment include field data (temperature, pH, conductivity, dissolved oxygen, and redox sensitive solutes), solute concentrations, and sediment composition. Dissolved inorganic carbon concentrations indicate that bicarbonate and carbonate are typically the most abundant anions in these systems. Speciation calculations reveal that ferrous iron typically exists as FeCO3(aq), FeHCO3 +, FeSO4(aq), or Fe2+ in these systems. The abundance of ferrous carbonate and bicarbonate species appears to lead to a dramatic increase in the abiotic rate of reaction compared to the rate expected from chemical oxidation in dilute solution. This approach, integrating geochemistry, rates, and community composition, reveals locations and geochemical conditions that permit microbial iron oxidation and locations where the abiotic rate is too fast for the biotic process to compete.

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Rather than focusing on the structural details of a specific natural protein, we are designing general protein structural scaffolds (''maquettes'') to accommodate a variety of functions. Here we will present transmembrane electron transfer via AP6, an amphiphilic tetra-helical maquette that binds up to 6 hemes. We demonstrate that AP6 self-assembles with phospholipids into vesicles. Our stop flow experiments confirm that the AP6 maquette significantly increases the electron transfer rates between oxidizing interior and an external redox mediator dye, as shown below.