Differential protein abundance of vetiver grass in response to acid mine drainage.

Acid mine drainage (AMD) is an acidic and metalliferous discharge that imposes oxidative stress on living things through bioaccumulation and physical exposure. The abandoned Tab-Simco mining site of Southern Illinois generates highly acidic AMD with elevated sulfate (SO4 2- ) and various metals. Vetiver grass (Chrysopogon zizanioides) is effective for the remediation of Tab-Simco AMD at both mesocosm and microcosm levels over extended periods. In this study, we conducted a proteomic investigation of vetiver shoots under short and long-term exposure to AMD. Our objective was to decipher the physiological responses of vetiver to the combined abiotic stresses of AMD (metal and low pH). Differential regulation was observed for longer-term (56 days) exposure to AMD, which resulted in 17 upregulated and nine downregulated proteins, whereas shorter-term (7 days) exposure led to 14 upregulated and 14 downregulated proteins. There were significant changes to photosynthesis, including upregulation of electron transport chain proteins for light-dependent reactions after 56 days, whereas differential regulation of enzymes relating to C4 carbon fixation was observed after 7 days. Significant changes in amino acid and nitrogen metabolism, including upregulation of ethylene and flavonoid biosynthesis, along with plant response to nitrogen starvation, were observed. Short-term changes also included upregulation of glutathione reductase and methionine sulfoxide reductase, whereas longer-term changes included changes in protein misfolding and ER-associated protein degradation for stress management and acclimation.

Metabolic response of vetiver grass (Chrysopogon zizanioides) to acid mine drainage.

Acid mine drainage (AMD) is a sulfuric discharge containing metals and particulates that can spread to nearby water sources, imposing toxicity and physical stress to living things. We have shown that vetiver grass (Chrysopogon zizanioides) is capable of tolerating and treating AMD-impacted water from the abandoned Tab-Simco mining site from southern Illinois, though little is known about its tolerance mechanisms. We conducted metabolomic analyses of vetiver shoots and roots after relatively short- and long-term periods of exposure to Tab-Simco AMD. The metabolic shift of vetiver shoots was dramatic with longer-term AMD exposure, including upregulation of amino acid and glutathione metabolism, cellular respiration and photosynthesis pathways, with downregulation of phosphorylated metabolites. Meanwhile, the roots demonstrated drastic downregulation of phospholipids and phosphorylated metabolites, cellular respiration, glyoxylate metabolism, and amino acid metabolism. Vetiver accumulated ornithine and oxaloacetate in the shoots, which could function for nitrogen storage and various intracellular functions, respectively. Organic acids and glutathione were secreted from the roots for rhizospheric metal-chelation, whereas phosphorylated metabolites were recycled for phosphorus. These findings reveal AMD-induced metabolic shifts in vetiver grass, which are seemingly unique in comparison to independent abiotic stresses reported previously.

A preliminary study to design a floating treatment wetland for remediating acid mine drainage-impacted water using vetiver grass (Chrysopogon zizanioides).

Acid mine drainage (AMD) is extremely acidic, sulfate-rich effluent from abandoned or active mine sites that also contain elevated levels of heavy metals. Untreated AMD can contaminate surface and groundwater and pose severe ecological risk. Both active and passive methods have been developed for AMD treatment consisting of abiotic and biological techniques. Abiotic techniques are expensive and can create large amounts of secondary wastes. Passive biological treatment mainly consists of aerobic or anaerobic constructed wetlands. While aerobic wetlands are economical, they are not effective if the pH of the AMD is < 5. Anaerobic wetlands use organic-rich substrates to provide carbon source to iron- and sulfate-reducing bacteria. The efficiency of these systems declines overtime and requires continuous maintenance. Our objective is to develop an alternative, low-cost, and sustainable floating wetland treatment (FWT) system for AMD for the abandoned Tab-Simco coal mining site in Illinois using vetiver grass (Chrysopogon zizanioides). Tab-Simco AMD is highly acidic, with mean pH value of 2.64, and contains high levels of sulfate and metals. A greenhouse study was performed for a 30-day period in order to screen and optimize the necessary parameters to design a FWT system. Water quality and plant growth parameters were continuously monitored. Results show significant SO42- removal, resulting in increased pH, particularly at higher planting densities. Vetiver also helped in metal removal; high amounts of Fe, Zn, and Cu were removed, with relatively lower amounts of Pb, Al, and Ni. Iron plaque formation on the root was observed, which increased metal stabilization in root and lowered root to shoot metal translocation. Vetiver was tolerant of AMD, showing minimal change in biomass and plant growth. Results obtained are encouraging, and a large scale mesocosm study is now in progress, as the next step to develop the vetiver-based system for AMD treatment.