Superoxide-Producing Fungus Sponges Up Mine Metals

Manganese oxides are environmental sponges that scavenge and sequester toxic metals such as lead, copper, and zinc, making them effective in cleaning up coal mine drainage. In their efforts to improve mine drainage treatment, researchers have struggled to understand how microorganisms, generally thought to be bacteria, oxidize soluble Mn(II) to precipitate manganese oxides in these systems. Now Colleen M. Hansel, a microbial geochemist at Harvard University and Woods Hole Oceanographic Institution, and colleagues have found that the key to some successful treatment systems is not bacteria but a fungus (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1203885109). Combining light microscopy with synchrotron-based X-ray absorption spectroscopy and fluorescence microscopy, the researchers showed that a common ascomycete fungus found in mine drainage treatment systems oxidizes Mn(II) by producing superoxide extracellularly during reproduction. This superoxide reacts with Mn(II), causing precipitation of brown Mn(III) and Mn(IV) oxides on the base of the fungus’ reproductive structures. The work could help in bioremediating acid mine drainage, says Bradley M. Tebo, a microbiologist at Oregon Health & Science University.