Microbial transformation of magnetite to hematite

A microbial consortium enriched from surface water draining the Lac du Bonnet granitic batholith in Manitoba, Canada, was able to mediate the transformation of 11% of the Fe in a sample of magnetite into hematite within three weeks. Holes, up to 100 mu m in diameter, were formed in grains of magnetite in a polished section of granite that had been exposed to a microbial biofilm in the laboratory. Bacteria were seen by scanning electron microscopy to be attached to magnetite after three days incubation in a flask, while a covering of biofilm was nearly complete after six days. Some hexagonal grains of an iron mineral were visible after incubation for eight weeks. Dissolution of the magnetite and the presence of hematite in the incubated flasks was confirmed by Mossbauer spectra and powder X-ray diffraction patterns. No hematite was found either in the original sample of magnetite or in duplicate sterile controls. Copyright (C) 1997 Elsevier Science Ltd.