Reductive dissolution of ferric iron minerals by Acidiphilium SJH

The acidophilic heterotrophic eubacterium Acidiphilium SJH was shown to cat alyze the reductive dissolution of a wide range of ferric iron-containing m inerals (akageneite, goethite, jarosite, natrojarosite, and amorphous ferri c hydroxide) and of the mixed ferrous/ferric mineral magnetite. The specifi c rates of dissolution varied with the structural stabilities of the minera ls, such that amorphous ferric hydroxide was the most rapid and jarosite an d akageneite were the slowest of the minerals tested. The reductive dissolu tion of both amorphous ferric hydroxide and magnetite was faster in pH 2.0 than in higher pH (2.8-3.0) cultures, even though Acidiphilium SJH has a pH optimum close to pH 3. Contact between bacteria and ferric mineral was not necessary for reductive dissolution to occur. Adding EDTA or diethylenetri amine pentaacetic acid to bacterial cultures accelerated the solubilization of goethite and amorphous ferric hydroxide. Although cell-free spent media and heat-killed Acidiphilium SJH also appeared to enhance mineral dissolut ion (indicated by formation of soluble Fe3+), this was far less extensive t han that in active bacterial cultures, and no iron reduction was observed i n the absence of viable cells. Experimental results suggested that Acidiphi lium SJH accelerates the reductive dissolution of ferric iron minerals by w ay of an indirect mechanism, in which bacterial reduction of soluble ferric iron causes a shift in equilibrium between solid phase (mineral) and solub le ferric iron, thereby causing further dissolution of the mineral.