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The incorporation of metal cofactors into protein active sites and/or active regions expanded the network of microbial metabolism during the Archean eon. The bioavailability of crucial metal cofactors is largely influenced by earth surface redox state, which impacted the timing of metabolic evolution. Vanadium (V) is a unique element in geo-bio-coevolution due to its complex redox chemistry and specific biological functions. Thus, the extent of microbial V utilization potentially represents an important link between the geo- and biospheres in deep time. In this study, we used geochemical modeling and network analysis to investigate the availability and chemical speciation of V in the environment, and the emergence and changing chemistry of V-containing minerals throughout earth history. The redox state of V shifted from a more reduced V(III) state in Archean aqueous geochemistry and mineralogy to more oxidized V(IV) and V(V) states in the Proterozoic and Phanerozoic. The weathering of vanadium sulfides, vanadium alkali metal minerals, and vanadium alkaline earth metal minerals were potential sources of V to the environment and microbial utilization. Community detection analysis of the expanding V mineral network indicates tectonic and redox influence on the distribution of V mineral-forming elements. In reducing environments, energetic drivers existed for V to potentially be involved in early nitrogen fixation, while in oxidizing environments vanadate ( VO 4 3 - ] ] > ) could have acted as a metabolic electron acceptor and phosphate mimicking enzyme inhibitor. The coevolving chemical speciation and biological functions of V due to earth's changing surface redox conditions demonstrate the crucial links between the geosphere and biosphere in the evolution of metabolic electron transfer pathways and biogeochemical cycles from the Archean to Phanerozoic., (© 2020 John Wiley & Sons Ltd.)

The dissolution of elemental selenium [Se(0)] during chemical weathering is an important step in the global selenium cycle. While microorganisms have been shown to play a key role in selenium dissolution in soils, the mechanisms of microbial selenium solubilization are poorly understood. In this study, we isolated a Bacillus species, designated as strain JG17, that exhibited the ability to dissolve Se(0) under oxic conditions and neutral pH. Growth of JG17 in a defined medium resulted in the production and accumulation of extracellular compounds that mediated Se(0) dissolution. Analysis of the spent medium revealed the presence of extracellular sulfite, sulfide, and thiosulfate. Abiotic Se(0) dissolution experiments with concentrations of sulfite, sulfide, and thiosulfate relevant to our system showed similar extents of selenium solubilization as the spent medium. Together, these results indicate that the solubilization of Se(0) by JG17 occurs via the release of extracellular inorganic sulfur compounds followed by chemical dissolution of Se(0) by the reactive sulfur metabolites. Our findings suggest that the production of reactive sulfur metabolites by soil microorganisms and the formation of soluble selenosulfur complexes can promote selenium mobilization during chemical weathering., (© 2018 John Wiley & Sons Ltd.)