This study used batch reactors to characterize the rates and mechanisms of elemental release during the interaction of a single bacterial species (Burkholderia fungorum) with Columbia River Flood Basalt at T = 28°C for 36 days. We primarily examined the release of Ca, Mg, P, Si, and Sr under a variety of biotic and abiotic conditions with the aim of evaluating how actively metabolizing bacteria might influence basalt weathering on the continents. Four days after inoculating P-limited reactors (those lacking P in the growth medium), the concentration of viable planktonic cells increased from $10 4 to 10 8 CFU (Colony Forming Units)/mL, pH decreased from $7 to 4, and glucose decreased from $1200 to 0 lmol/L. Mass-balance and acid-base equilibria calculations suggest that the lowered pH resulted from either respired CO 2 , organic acids released during biomass synthesis, or H + extrusion during NH 4 þ uptake. Between days 4 and 36, cell numbers remained constant at $10 8 CFU/mL and pH increased to $5. Purely abiotic control reactors as well as control reactors containing inert cells ($10 8 CFU/mL) showed constant glucose concentrations, thus confirming the absence of biological activity in these experiments. The pH of all control reactors remained near-neutral, except for one experiment where the pH was initially adjusted to 4 but rapidly rose to 7 within 2 days. Over the entire 36 day period, P-limited reactors containing viable bacteria yielded the highest Ca, Mg, Si, and Sr release rates. Release rates inversely correlate with pH, indicating that proton-promoted dissolution was the dominant reaction mechanism. Both biotic and abiotic P-limited reactors displayed low P concentrations. Chemical analyses of bacteria collected at the end of the experiments, combined with mass-balances between the biological and fluid phases, demonstrate that the absence of dissolved P in the biotic reactors resulted from microbial P uptake. The only P source in the basalt is a small amount of apatite ($1.2%), which occurs as needles within feldspar grains and glass. We therefore conclude that B. fungorum utilized apatite as a P source for biomass synthesis, which stimulated elemental release from coexisting mineral phases via pH lowering. The results of this study suggest that actively metabolizing bacteria have the potential to influence elemental release from basalt in continental settings.

The effects of a series metal dopants on the photocatalytic activity of SrTiO 3 -based photocatalyst are investigated using first principle DFT calculations. The SrTiO 3 :Rh(1%) loaded with Pt has been found to give the best efficiency in water splitting. However, the same host doped with Ru leads to very low H 2 evolution rate even it has a better visible light response. The analysis of the density of states and the calculated absorption spectra were used to illustrate the mechanisms that influence the photocatalytic efficiency. Our calculation results suggested that the two competing factors, the free electron generation (via light harvesting) and the charge recombination (due to the presence of recombination centers) process resulted in the existence of the optimal dopant concentration for the transition-metal-doped SrTiO 3 lattice. The energy states introduced by dopant Rh in the bandgap of SrTiO 3 were found to be very close to the valence band maximum. These new states thus reduce the bandgap of catalyst and enhance its light absorption capability. Furthermore, the proximity of these states to the valence band allows for efficient electron replenishment and thus reduces the probability of trapping electrons from the conduction band. In contrast, the energy states introduced by dopant Ru are significantly higher than the valence band making them an isolated recombination center. These Ru associated states also reduces the driving force for oxidation reaction. As a result, the Rh-doped SrTiO 3 catalysts are found to provide a high H 2 evolution rate.

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