微生物铁还原作用对蒙脱石保存有机物的影响:以硫酸盐还原菌为例

本文研究了微生物的铁还原作用对黏土矿物有机质保存的影响。将一种有机化合物(十二氨基十二酸)插层到一种富铁的蒙脱石(绿脱石)中,利用硫酸盐还原菌(Desulfovibrio vulgaris)分别对插层前后的绿脱石进行作用,以研究该菌对绿脱石结构中Fe3+的还原作用以及层间有机物的影响。结果发现,1Desulfovibrio vulgaris能够还原这2种绿脱石结构中的Fe3+,且电子穿梭体AQDS(蒽醌-2,6-二磺酸)能够增强还原速率和程度;2硫酸盐的存在能够增加还原速率和程度,表明还原过程中生成的硫化物与绿脱石结构中的Fe3+发生了化学还原作用;3通过X射线衍射、红外光谱、总有机碳分析表明,还原后的绿脱石,其结构层内仍有大量有机物,具有一定的稳定性和保存层间有机质的能力。     

不动杆菌属菌株WX-19还原Cr（Ⅵ）与降解苯酚特性

从制革废水中筛选到1株既能还原Cr（Ⅵ）又能降解苯酚的不动杆菌属（Acinetobacter）菌株WX-19。菌株降解苯酚和还原Cr（Ⅵ）的最适温度为30℃,最适pH为7.0～8.0。0.2～0.5 mol/L NO3-、SO42-和Cl-能够促进WX-19的生长及其对Cr（Ⅵ）的还原。利用PCR、克隆和基因测序的方法从WX-19中检测到苯酚羟化酶基因（GenBank No.JF730215）,与Pseudomonas sp.DHS3Y的苯酚羟化酶基因的同源性为88.5%。在含5 mg/LCr（Ⅵ）的基础盐培养基中,菌株WX-19可以利用苯酚为唯一碳源生长,并还原Cr（Ⅵ）;在含有葡萄糖的基础盐培养基中,添加苯酚有利于菌株WX-19的生长和Cr（Ⅵ）还原。     

海洋真菌Rhodotorulamucilageinosa GIM 2.157介导邻-、间-、对-溴苯乙酮的不对称还原反应

研究了海洋真菌介导邻-、间-、对-溴苯乙酮的不对称还原反应。具体考察了Rhodotorulamucilageinosa GIM 2.157对邻-、间-、对-溴苯乙酮的催化活性和对映选择性,并综合考察了反应温度、pH、反应时间和底物浓度等因素对还原产物的产率及立体选择性的影响。确定最佳反应条件:反应温度为25℃,反应体系的pH为7,反应时间为24 h,底物浓度为10 mmol/L。在最佳条件下,产率以及立体选择性均99%。     

Coupled uranium mineralisation and bacterial sulphate reduction for the genesis of the Baxingtu sandstone-hosted U deposit,SW Songliao Basin,NE China

The Baxingtu deposit is a typical redox front tabular-shaped uranium deposit hosted in sandstones of the Late Cretaceous Yaojia Formation deposited within a braided river environment during the post-rift stage of the Songliao Basin, in northeast China. This study proposes the first metallogenic model for the Baxingtu deposit and provides new data on genetic processes involved in the uranium mineralisation of sandstone-type deposits that were characterised through petrographic observations, whole-rock geochemistry, and geochemical and/or mineralogical study of iron disulphide, uranium minerals, Fe-Ti oxides (EPMA, LA-ICP-MS), and organic matter (REP). The δ³⁴S value has been measured in situ by SIMS on the different generations of iron disulphide.Within regional primary reduced sandstones, pre-ore uranium enrichment (U_mean = 7.6 ppm in whole rock) was identified on altered Fe-Ti oxides along with minor concentrations on organic matter (respectively 26.3% and 1.3% of the whole-rock U content), which together represent a significant source of uranium for the mineralisation. Additional pre-ore uranium concentrations may also be associated with clay minerals. Petrographic observations and REP data indicate that organic matter occurring in the host-sandstone is mainly inherited from land plants and corresponds to type III or type IV kerogens. Ore-stage iron disulphides largely occur as framboids and in replacement of organic matter or also as sub-idiomorphic to idiomorphic cement and crystal. Trace element signatures detected within framboids are likely indicative of formation mainly from a single event. Framboids and iron disulphide in replacement of organic matter have a light sulphur isotope signature characterised by δ³⁴S values from −72.0 to −6.2‰, suggesting that sulphur originated from bacterial sulphate reduction, which was mainly responsible for (1) the liberation of U from Fe-Ti oxides and organic matter, (2) the generation of ore-stage iron disulphides, (3) the bioreduction of uranium and (4) the production of a secondary H₂S-rich reducing barrier also involved in uranium reduction. Uranyl and sulphate ions were transported through the host sandstone by low-temperature oxygenated groundwater and U(IV) was precipitated at the redox interface as nano to microcrystals of pitchblende and coffinite, dominantly associated with bacterial substrate and as intergrowth with biogenic iron disulphide or directly associated with organic matter and residual Ti-Fe oxides. The uranium mineralisation does not replace ore-stage iron disulphides. Therefore, the combined mineralogical, geochemical, and isotopic characteristics of the Baxingtu tabular uranium deposit characterise dominantly biogenic processes for the genesis of the uranium mineralisation.