Plant Growth-Promoting Bacteria Suitable for the Phytostabilization of Mine Tailings

Mining activities and their resulting wastes, mine tailings, have created a sizable problem globally. Semiarid lands have been particularly impacted due to intense mining activities in these areas. Growing concerns regarding human health risks and environmental consequences associated with these tailings has created a need for efficient and effective remediation strategies. Phytostabilization, the establishment of a vegetative cover on mine tailings to reduce erosion and dispersion of material, is emerging as a cost-effective remediation technology. However, due to elevated levels of metal contaminants, acidic pH values and poor substrate quality many tailings sites are inhospitable to plant growth. The addition of compost amendments can mitigate the toxic effects of tailings material and facilitate plant growth; however, in many instances the necessary compost amendments may be cost prohibitive. The use of specialized bacterial isolates, known as plant growth-promoting bacteria (PGPB), to enhance plant growth is a developing technology that has a broad range of applications. The use of PGPB to enhance one or more aspect of plant establishment and growth has been demonstrated to be effective in hundreds of previous studies conducted primarily under agricultural settings. To date, very few studies have utilized PGPB in attempts to enhance plant growth in mine tailings. The current study is an investigation into the potential for utilizing PGPB to enhance plant growth during the phytostabilization of semiarid mine tailings. During this investigation a large collection of bacterial isolates was screened for common plant growth-promoting mechanisms such as siderophore and indole-3-acetic acid production, phosphate solubilization and ACC-deaminase activity. Isolates possessing beneficial qualities were utilized in a series of greenhouse screening studies to evaluate their abilities to enhance the growth of native desert plants in various tailings materials. A number of isolates tested have demonstrated the ability to enhance plant growth in composted and non-composted tailings material. Optimization of this technology has now indicated that alginate-encapsulated inoculation of target plants is a beneficial and practical technology