Mineral Formation And Environmental Applications Driven By Extracellular Redox Reactions Of Iron/Manganese Metabolizing Bacteria

The oxidizing/reducing power of iron and manganese metabolizing bacteria?IMMB?enables their applications in various environmental fields.Although there are some reports about the environmental applications of IMMB,the mechanism of trace elemental mineralization,isolation and application of bio-prepared nanomaterials and the interaction between elemental cycling and contaminant degradation remain unrevealed.In this thesis,we investigated on the roles of several representative IMMB in trace elemental mineralization,nanomaterials biosynthesis,and antibiotics degradation induced by elemental cycling.The main research contents and results are provided as follows:1.With the widely concerned and relatively abundant selenium as a representative trace element group,ferrihydrite as an iron-based mineral and Geobacter sulfurreducens as an IMMB,the trace elemental mineralization mediated by IMMB was investigated.The surface characterization results show that G.Sulfurreducens could induce co-reduction of ferrihydrite and selenite and iron selenide was formed in a long term?120 d?.In addition,the effects of electron donor and electron shuttle on such a biomineralization were confirmed.Hydrogen,serving as an electron donor,was found to be able to facilitate iron reduction but reduce cell viability.Dose of electron shuttle could accelerate the iron-reducing rate and compensate the insufficiency of acetate as an electron donor.2.The strong extracellular reducing power and wide electron acceptor-utilizing capacity of an iron and manganese reducing bacterium,Shewanella oneidensis MR-1 was used to form nanomaterials.S.oneidensis could reduce S2O32-into S2-,the formed S2" combined with Cu2+ subsequently,generating CuS nanoparticles?NPs?.The isolating and purifying methods of the biosynthesized CuS NPs were simplified by controlling the initial ratio of sulfur to copper,and uniformed,small-sized and highly dispersed CuS NPs were obtained.The biosynthesized CuS NPs exhibited a high photothermal conversion efficiency and good stability according to the results of photothermal conversion measurement.Moreover,the in vitro experiment using A594R cell lines showed that the bio-prepared CuS NPs were able to kill cancer cells efficiently without hurting healthy tissues.3.With the involvement of manganese oxide,a pollutant degradation system with both biotic and abiotic cycles was established.In such a system,Pseudomonas putida MnB-1 was used to oxidize Mn²⁺ and highly reactive MnO2 was obtained to accomplish the degradation of ciprofloxacin?CEP?.Since the bacterial cells remained active in the presence of MnO2,they were able to partially re-oxidize MnO2,which had been reduced through reacting with CIP.As a result,bio-induced manganese cycling and manganese-induced CIP degradation could be achieved.Furthermore,dosing Mn?III?complex into the system reduced the CIP degradation,suggesting the acceleration role of Mn?III?in this system.