Selective dissolution of iron minerals in acid mine drainage and iron-oxidizing microbial communities for the purpose of measuring nanowire conductivity

Abstract

Similar structures were detected in neutrophilic iron-oxidizing cultures that were treated with 200 mM ammonium oxalate solution to gently dissolve biogenic minerals that would otherwise obscure visualization of the biological filaments. Samples prepared by these methods appear to be of sufficient quality to be analyzed for conductivity using established scanning tunneling or conductive atomic form microscopy. If these structures prove conductive, this would represent the first confirmation of electrically conductive appendages in iron oxidizing microbial systems.

A laboratory system was designed to generate microbial biofilms from a variety of iron oxidizing communities. Microbial communities of acid mine drainage can be induced to dissolve their mineral phases with the addition of a readily usable electron donor, such as dextrose, in the absence of oxygen. Mineral dissolution in acid mine drainage cultures exposes several features previously hidden within the iron phases of the culture. Scanning electron microscopic evidence revealed the presence of extracellular appendages that morphologically resemble electrically conductive “bacterial nanowires” produced by a number of iron reducing microbes, such as Shewanella oneidensis.