Dissimilatory iron reducing microorganisms in South Mid-Atlantic Ridge hydrothermal fields and their mineralized products

Abstract:

[Objective] To obtain the dissimilatory iron reducing microorganisms (DIRM) from deep sea hydrothermal fields, analyze their mineralization ability and mineralization products, to further understand their role in iron biogeochemical cycle. [Methods] We enriched and cultivated DIRM from polymetallic sulfides of South Mid-Atlantic Ridge hydrothermal fields with FeOOH as an electron acceptor, and acetic acid etc. as electron donor under the constant 60℃ temperature anaerobic condition. The morphology observation and elemental composition analysis on mineralized products were carried out by scanning electron microscope, transmission electron microscope, selected area electron diffraction and Energy Dispersive Spectrometer. [Results] We obtained a total of 139 iron reducing microbial cultures from 2 polymetallic sulfides. All of them could transform FeOOH (Fe³⁺ 90 mmol/L) into mineralized iron products with obvious crystal structure, mainly in cubic shape with side length ranged from 5.0 nm to 20.0 nm. According to Energy Dispersive Spectrometer analysis, the elements of all mineral crystals were iron and oxygen, presumably a mixed mineral composed crystal of siderite and magnetite. The time of formation of mineral crystals varies from 3 to 54 d, and most cultures can form crystals within 11 to 20 d. Microbial diversity indicated that the dominant microorganisms in the culture were mainly Firmicutes and Euryarchaeota, including Carboxydocella and Desulfotomaculum, a new species (16S rRNA Homology 89%-91%) and Geoglobus. [Conclusion] At 60℃, bacteria and archaea in hydrothermal fields could transform ferric iron to mixed iron oxides mineral with the simple organic compounds as electron donor. These results supported the potential of microorganisms to participate in the biogeochemical cycle and mineralization. However, it requires extensive research work to verify their roles in situ.