Metallophore Activity toward the Rare Earth Elements by Bacteria Isolated from Acid Mine Drainage Due to Coal Mining

Abstract

The field of microbe–metal interactions has been gaining significant attention. While the direct impact of metal oxyanions on bacteria has been investigated, significantly less attention has been placed on the ability of certain microbes to ‘collect’ such metal ions via secreted proteins. Many bacteria possess low-weight molecules called siderophores, which collect Fe from the environment to be brought back to the cell. However, some appear to have additional roles, including binding other metals, termed ‘metallophores’. Microbes can remove/sequester these from their surroundings, but the breadth of those that can be removed is still unknown. Using the Chromeazurol S assay, we identified eight isolates, most belonging to the genus Pseudomonas, possessing siderophore activity, mainly from sites impacted by coal mine drainage, also possessing a metallophore activity toward the rare earth elements that does not appear to be related to ionic radii or previously reported EC50 concentrations for E. coli. We found the strength of metallophore activity towards these elements was as follows: Pr > Sc > Eu > Tm > Tb > Er > Yb > Ce > Lu > Sm > Ho > La > Nd > Dy > Gd > Y. This is the first study to investigate such activity and indicates bacteria may provide a means of removal/recovery of these critical elements.

Chryseobacterium metallicongregator, sp. nov., a bacterium possessing metallophore activity towards rare earth elements

“…Strain ES2 T was isolated from damp surface sediment of a wetland created to remediate acid drainage from a coal mine [14, 17]. The pH of the sediment sampled was pH 6.5.…”

“…In this study, we aim to taxonomically classify strain ES2 T , a novel Chryseobacterium species isolated from sediment of a wetland created to remediate acid mine drainage from a coal mine. This bacterium is of special interest as it has been shown to produce a siderophore as well as having metallophore activity towards the rare earth elements [14], an extremely unique ability which is of great interest for potential recovery/recycling of this group [16]. With an increased interest in obtaining these highly important elements, a biological method could be of great use in biomining, with strains producing metallophores having a significant role in the process.…”

“…Many metal-tolerant bacteria capable of producing these compounds have received more attention over the years due to their numerous potential applications in bioremediation [12,13]. Studies have shown that metallophores have an affinity for a wide range of metals, including copper, zinc, nickel, selenium, tellurium, cobalt as well as the rare earth elements [11,14,15]. This makes them ideal in bioremediation projects involving mine waste material and soil contaminated with high concentrations of metals [11].…”