Metal reduction and biomineralization by an alkaliphilic metal-reducing bacterium,Alkaliphilus metalliredigens (QYMF)

Abstract

Microbial metal reduction has the potential for immobilizing toxic metals and radionuclides in diverse environments. Little is known about metal reduction and immobilization under extreme conditions, and only recently bacterial reduction of metals has been demonstrated under extremely alkaline conditions. The objective of this study was to examine metal reduction and mineral formation using an alkaliphilic bacterium,Alkaliphilus metalliredigens (QYMF), isolated from a leachate-pond containing high levels of salt (Na concentration = 440–12,100 mg/L) and boron (2,000–3,000 mg/L) at pH 9.0–10.0. The bacterium was able to use lactate, acetate, and hydrogen as alternative electron donors and Fe(III)-citrate, Fe(III)- ethylenediaminetetraacetate (EDTA), selenate (SeO4 2−), chromate (CrO4 2−), and Co(III)-EDTA as electron acceptors at medium pH=9.5. The reduction of Fe(III)-citrate and Fe(III)-EDTA in the presence of K2HPO4 and boron resulted in the precipitation of vivianite [Fe3(PO4)2·8H2O]. Formation of sparingly soluble iron phosphates, mediated by the alkaliphilic Fe(III)-reducing bacterium, sequestered iron, phosphate, and other metals into more stable and less toxic forms. These results suggest that bioremediation of metal-contaminated alkaline environments may be feasible, and that the process of metal-reduction may occur in alkaline habitats.