Using metabolic charge production in the tricarboxylic acid cycle (QTCA) to evaluate the extracellular-electron-transfer performances of Shewanella spp

Using an electrochemical cell equipped with carbon felt electrodes (poised at +0.63 V vs. SHE), the current production capabilities of two Shewanella strains-NTOU1 and KR-12-were examined under various conditions with lactate as an electron donor. The metabolic charge produced in the tricarboxylic acid cycle (Q_TCA) was calculated by mass-balance. The data showed a linear relation between the electric coulomb production (Q_EL) and Q_TCA with an R² of 0.65. In addition, a large amount of pyruvate accumulation was observed at pH = 6, rendering Q_TCA negative. The results indicate an occurrence of an undesired cataplerotic reaction. It was also found that Q_TCA provides important information showing the oxygen-boosting TCA cycle and anodic-current generation of Shewanella spp. Linear dependence of the change in charge for biomass growth (4.52FΔn_Cell) on Q_TCA was also found as expressed by 4.52FΔn_Cell = 1.0428 Q_TCA + 0.0442, indicating that these two charge quantities are inherently identical under most of the experimental conditions. In the mediator-spiked experiments, the external addition of the mediators (ferricyanide, anthraquinone-2, 6-disulfonate, and riboflavin) beyond certain concentrations inhibited the activity of the TCA cycle, indicating that the oxidative phosphorylation is deactivated by excessive amounts of mediators, yet Shewanella spp. are constrained with regard to carrying out the substrate-level phosphorylation.

Assessment of trace element impacts on agricultural use of water from the Dan River following the Eden coal ash release

Catastrophic events require rapid, scientifically sound decision making to mitigate impacts on human welfare and the environment. The objective of this study was to analyze potential impacts of coal ash-derived trace elements on agriculture following a 35,000-tonne release of coal ash into the Dan River at the Duke Energy Steam Station in Eden, North Carolina. We performed scenario calculations to assess the potential for excessive trace element loading to soils via irrigation and flooding with Dan River water, uptake of trace elements by crops, and livestock consumption of trace elements via drinking water. Concentrations of 13 trace elements measured in Dan River water samples within 4 km of the release site declined sharply after the release and were equivalent within 5 d to measurements taken upriver. Mass-balance calculations based on estimates of soil trace-element concentrations and the nominal river water concentrations indicated that irrigation or flooding with 25 cm of Dan River water would increase soil concentrations of all trace elements by less than 0.5%. Calculations of potential increases of trace elements in corn grain and silage, fescue, and tobacco leaves suggested that As, Cr, Se, Sr, and V were elements of most concern. Concentrations of trace elements measured in river water following the ash release never exceeded adopted standards for livestock drinking water. Based on our analyses, we present guidelines for safe usage of Dan River water to diminish negative impacts of trace elements on soils and crop production. In general, the approach we describe here may serve as a basis for rapid assessment of environmental and agricultural risks associated with any similar types of releases that arise in the future.