BIOGEOCHEMICAL AND ENVIRONMENTAL FACTORS IN Fe BIOMINERALIZATION: MAGNETITE AND SIDERITE FORMATION

摘要

The formation of siderite and magnetite by Fe(Ⅲ)-reducing bacteria may play an important role in C and Fe geochemistry in subsurface and ocean sediments. The objective of this study was to identify environmental factors that control the formation of siderite (FeCO_3) and magnetite (Fe_3O_4) by Fe(Ⅲ)-rcducing bacteria. Psychrotolerant (<20℃), mesophilic (20-35℃) and thermophilic (>45℃) Fe(Ⅲ)-reducing bacteria were used to examine the reduction of a poorly crystalline iron oxide, akaganeitc (β-FeOOH), without a soluble electron shuttle, anthraquinone disulfuonate (AQDS), in the presence of N_2, N_2-CO_2(80:20, V:V), H_2 and H_2-CO_2 (80:20, V:V) headspace gases as well as in HCO_3~--buffered medium (30-210 mM) under a N_2 atmosphere. Iron biomineralization was also examined under different growth conditions such as salinity, pH, incubation time, incubation temperature and electron donors. Magnetite formation was dominant under a N_2 and a H_2 atmosphere. Siderite formation was dominant under a H_2-CO_2 atmosphere. A mixture of magnetite and siderite was formed in the presence of a N_2-CO_2 headspace. Akaganeite was reduced and transformed to siderite and magnetite in a HCO_3~--buffered medium (>120 mM) with lactate as an electron donor in the presence of a N_2 atmosphere. Biogeochemical and environmental factors controlling the phases of the secondary mineral suite include medium pH, salinity, electron donors, atmospheric composition and incubation time. These results indicate that microbial Fe(Ⅲ) reduction may play an important role in Fe and C biogeochemistry as well as C sequestration in natural environments.