BACKGROUND Mn oxides occur in a wide variety of geological settings and exert considerable influences on the components and chemical behaviors of sediments and soils. Microbial reduction of Mn oxides is an important process found in many different environments including marine and freshwater sediments, lakes, anoxic basins, as well as oxic-anoxic transition zone of ocean. Although the pathway of Mn anaerobic reduction by two model bacteria, Geobacter and Shewanella, has been intensively studied, Mn bio-reduction is still the least well-explored process in nature. Particularly, reduction of Mn oxides by other bacteria and in the presence of O2 has been fewly reported in recent publishes. RESULTS A series of experiments were conducted to understand the capability of Dietzia DQ12-45-1b in bioreduction of birnessite. In anaerobic systems, Mn reduction rate reached as high as 93% within 4 weeks when inoculated with 1.0 × 10(10) cells/mL Dietzia DQ12-45-1b strains. Addition of AQDS enhanced Mn reduction rate from 53 to 91%. The anaerobic reduction of Mn was not coupled by any increase in bacterial protein concentration, and the reduction rate in the stable stage of day 2-14 was found to be in good proportion to the protein concentration. The anaerobic reduction of birnessite released Mn(II) either into the medium or adsorbed on the mineral or bacteria surface and resulted in the dissolution of birnessite as indicated by XRD, SEM and XANES. Under aerobic condition, the reduction rate was only 37% with a cell concentration of 1.0 × 10(10) cells/mL, much lower than that in parallel anaerobic treatment. Bacterial growth under aerobic condition was indicated by time-course increase of protein and pH. In contrast to anaerobic experiments, addition of AQDS decreased Mn reduction rate from 25 to 6%. The reduced Mn(II) combined with carbon dioxide produced by acetate metabolism, as well as an alkaline pH environment given by cell growth, finally resulted in the formation of Mn(II)-bearing carbonate (kutnohorite), which was verified by XRD and XANES results. The system with the highest cell concentration of 1.0 × 10(10) cells/mL gave rise to the most amount of kutnohorite, while concentration of Mn(II) produced with cell concentration of 6.2 × 10(8) cells/mL was too low to thermodynamically favor the formation of kutnohorite but result in the formation of aragonite instead. CONCLUSION Dietzia DQ12-45-1b was able to anaerobically and aerobically reduce birnessite. The rate and extent of Mn(IV) reduction depend on cell concentration, addition of AQDS or not, and presence of O2 or not. Meanwhile, Mn(IV) bioreduction extent and suspension conditions determined the insoluble mineral products.

中文翻译：

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新型Dietzia菌株对水钠锰矿的有氧和厌氧还原。

背景技术锰氧化物存在于多种地质环境中，并对沉积物和土壤的成分和化学行为产生相当大的影响。锰氧化物的微生物还原是在许多不同环境中发现的重要过程，这些环境包括海洋和淡水沉积物，湖泊，缺氧盆地以及海洋的氧-缺氧过渡带。尽管已经深入研究了两种典型细菌（Geobacter和Shewanella）对Mn厌氧还原的途径，但Mn生物还原仍然是自然界中研究最少的过程。特别是，在最近的出版物中几乎没有报道过由其他细菌和在氧气的存在下还原锰氧化物。结果进行了一系列的实验，以了解Dietzia DQ12-45-1b在水钠锰矿的生物还原中的能力。在厌氧系统中 当接种1.0×10（10）细胞/ mL Dietzia DQ12-45-1b菌株后，Mn还原率在4周内高达93％。加入AQDS可使锰的还原率从53％提高到91％。锰的厌氧还原与细菌蛋白质浓度的增加没有关联，并且发现在第2-14天的稳定阶段还原速度与蛋白质浓度成正比。如XRD，SEM和XANES所示，水钠锰矿的厌氧还原将Mn（II）释放到培养基中或吸附在矿物或细菌的表面上，并导致水钠锰矿的溶解。在有氧条件下，细胞浓度为1.0×10（10）细胞/ mL时，还原率仅为37％，远低于平行厌氧处理时的还原率。有氧条件下细菌的生长通过蛋白质和pH值随时间的增加来指示。与厌氧实验相反，添加AQDS将Mn的还原率从25％降低至6％。还原的Mn（II）与乙酸盐代谢产生的二氧化碳以及细胞生长赋予的碱性pH环境相结合，最终导致形成了Mn（II）的碳酸盐（方铁矿），并通过XRD和XRD验证了这一点。 XANES结果。最高细胞浓度为1.0×10（10）个细胞/ mL的系统产生的kutnohorite数量最多，而细胞浓度为6.2×10（8）个细胞/ mL时产生的Mn（II）浓度太低热力学上有利于形成苦硼钙石，但反而导致了文石的形成。结论Dietzia DQ12-45-1b能够厌氧和好氧还原水钠锰矿。Mn（IV）还原的速率和程度取决于细胞浓度，是否添加AQDS以及是否存在O2。同时，Mn（IV）的生物还原程度和悬浮条件决定了不溶性矿物质。