The Mechanisms Of Iron-reduction And Biomineralization Of Two Fermentative Dissimilatory Iron-reducing Bacteria From Deep-sea Hydrothermal Fields

Dissimilatory iron reduction microbes(DIRBs), defined as one type of microbes which can reduce Fe(III) to Fe(Ⅱ) with organics as electron donor and Fe(III) as extracellular electron acceptor. These microbes spread over anoxic environments, playing an important role in iron geochemical cycle and Fe(III)-minerals reduction, migration, transformation.The main metabolites were acetate、butyrate、H2、CO2 with peptone as electron donor and soluble ferric citrate、insoluble Fe OOH as electron acceptor. The cell growth and concentration of acetate、butyrate、CO2 were higher with Fe(III) as electron acceptor than peptone fermentation alone. It indicated that dissimilatory iron reduction could accelerate the fermentation process and cell growth. But the concentration of H2 was lower with Fe(III) as electron acceptor than peptone fermentation alone. The iron reduction process restrained H2 production. The electrons was accepted by Fe(Ⅲ) partly coming from that possibly transferred to H+. Only few electrons were transferred to extracellular Fe(Ⅲ) by calculating the electron flow. Strain DY22613 T could reduce Fe(III) to Fe(II) and form magnetite particles using Fe OOH as electron acceptor. Nevertheless the black precipitates were amorphous iron-sulfur complex using ferric citrate as electron acceptor, indicating that sulfate reduction occured. Besides, there were gene clusters encoding NADH-hydrogenase and FAD-hydrogenase, but no multi-heme cytochrome C in the genome. Further research revealed that the FAD-hydrogenase participated in the electron transport in intracellular membrane. Meanwhile there were other proteins in periplasmic space and extracellar membrane functioning as electron transfer mediators rather than multi-heme cytochrome C. The results indicated that the strain may adopt another redox proteins to transfer electron different from breath-type dissimilatory iron-reduction microbes Geobacter spp. and Shewanella spp..The iron reduction capability of Caloranaerobacter ferrireducens DY22619 T was characterized. We compared the iron reduction rates with three different iron oxides as the electron acceptor, and analyzed the mineral morphology, element component and crystal face using Transmission Electron Microscope(TEM). The iron reduction rate was the highest during from exponential to stationary phase(48 h) and the rate with amorphous Fe OOH and amorphous Fe(III) Oxide was much higher reaching about 2.82 μmol /h and 2.15 μmol /h. TEM results showed the bacterium reduced all the three kinds of iron oxides and formed magnetite particles. The granule size of the magnetite formed with Goethite was the largest, but less in granule number. In addition, the crystal face derived from reducing amorphous Fe(III) oxide was different from other two oxides. The results indicated the strain has a high potential in iron reducing Fe(III) oxides and mineralization in anaerobic respiration. However, the properties of the magnetite and iron reduction rate were influenced by the characteristics of iron oxides.A. fermentans DY22613 T and C. ferrireducens DY22619 T are both fermentative DIRBs from deep-sea hydrothermal fields, belong to genus“Clostrida”. The results expand and develop our knowledge about the role of genus“Clostrida”in global iron cycle. They may participate the iron cycle and Fe(III)-minerals reduction, migration, transformation. in deep-sea hydrothermal fields with other iron-reduction microbes.