南方红壤微生物群落光电子能量响应特性

地表关键带中时刻发生的物质循环与能量流动过程使其成为地球最活跃的系统之一,其中即包含半导体矿物介导的非光合微生物利用太阳光能量这一微生物-矿物协同作用新途径。特别是富含半导体矿物的天然红壤,为研究关键带中半导体矿物转化太阳能为化学能或者生物质能的微观作用,探索关键带各圈层相互作用提供了新的契机。自海口、长沙两地采集天然红壤样品,经SEM、XRD等分析确定其含有针铁矿、赤铁矿、水钠锰矿等多种铁锰氧化物矿物,紫外可见漫反射吸收谱结果显示此类矿物对可见光具有较好的吸收活性。为考察矿物光电子能量对土壤微生物群落构成的影响,构建双室实验体系利用电化学恒电势技术模拟不同能量光电子,电势模拟矿物光电子能量设置为-0.05 V、-0.25 V(vs.SHE)。实验对比分析了土壤提取液、生理盐水、磷酸盐缓冲液、抗坏血酸溶液(提供有机空穴捕获剂)等不同介质条件下的电化学响应情况,发现0.1 mol/L NaH 2PO4缓冲液条件下体系稳定性最高,电流响应活性期超过30 d,最终体系稳定电流与溶液p H见表1。实验结果显示,阴极施加偏压条件下溶液p H基本稳定,说明水电解反应得以控制并达到动态平衡;恒定偏压下体系电流达到稳定,说明电极与表面微生物间电子转移的电化学过程实现平衡。同时,对比分析红壤样品的电流数据可以发现,海口、长沙两地样品在不同电势下的电流响应情况具有显著差异,预示着不同地区、不同电子能量作用下的微生物群落可能具有不同的响应特性。为进一步明确实验体系中微生物生长代谢状况,使用考马斯亮蓝G250测试总蛋白含量,对比初始阶段发现偏压作用前后蛋白含量基本稳定,表明模拟实验体系中微生物可维持原有代谢水平。本文构建双室电化学实验体系利用恒电势技术模拟不同能量光电子,考察微生物对光电子能量的响应特性。后续结合焦磷酸测序等技术获得群落构成信息,能够进一步揭示光电子能量响应情况下的红壤微生物群落演化特征。     

矿物光电子能量及矿物与微生物协同作用

本文总结了天然半导体矿物光电子能量及矿物与微生物协同作用的最新研究成果,特别强调地表微生物、矿物和太阳光多元复杂体系中金属氧化物和金属硫化物半导体矿物的可见光激发光电子特征,阐述了矿物光电子能量利于地球早期生命起源与演化、促进化能自养和化能异养微生物生长代谢、调控矿物与微生物协同作用实现固碳作用。进而提出矿物光电子能有效地将二氧化碳还原为有机物质,可为生命起源提供有机物质基础的认识。     

麦饭石促进异养反硝化去除水中硝酸盐的研究

微生物异养反硝化技术是市政污水处理中广泛应用的技术,但在实际应用中,微生物活性易受冲击负荷、重金属胁迫等环境条件影响,使出水效果不稳定。麦饭石作为一种天然硅酸盐矿物,能有效提高微生物活性及对环境胁迫的抗性,可以将其应用于微生物污染治理领域。通过批实验研究麦饭石的剂量、处理方式对异养反硝化的促进作用并探究麦饭石作用于微生物的机理。结果表明,麦饭石的投加剂量和处理方式均显著影响了微生物对硝酸盐的去除效果。硝酸盐去除率与麦饭石投加量呈正相关,麦饭石投加量为350 g/L时硝酸盐去除率可达96%,未添加麦饭石的空白组硝酸盐去除率仅为25%;处理方式会影响麦饭石对反硝化过程的强化作用,研磨后过200目筛的麦饭石在投加量<150 g/L时具有优势,投加量继续增大后,未经处理的麦饭石表现出更强的反硝化促进作用。进一步采用未经处理的麦饭石、研磨后过200目筛麦饭石及球磨麦饭石浸出液进行反硝化的促进实验及微生物毒性实验探究麦饭石作用于微生物的机理。实验结果表明,麦饭石浸出液能够提高微生物的活性及对环境胁迫的抗性,影响麦饭石生物促进作用的主要因素为其溶出微量元素的成分及浓度。本研究为天然矿物麦饭石应用于微生物污染治理提供理论依据和实际应用价值。     

化能自养型微生物利用太阳能途径的实验研究

针对自然界中天然半导体矿物和化能自养微生物之间的能量交换途径进行了详细的实验研究.半导体光电化学实验结果显示,天然半导体矿物在光照情况下产生的光生电子可将Fe3+还原为Fe2+,其中金红石光催化还原Fe3+的效率为12.5%,闪锌矿为7.86%,该过程通过天然半导体矿物的日光催化作用实现了太阳光能→电能→化学能的转化;控制电势的微生物电化学反应实验结果显示,化能自养型微生物A.f.菌的细胞增加量与外界电子传入而生成的Fe2+的量呈线性关系,且有外来电子传入实验组的A.f.生长量是无电子传入组的441%,该过程通过菌的生长代谢作用实现了化学能→生物质能的转化.进一步的光电化学和微生物电化学耦合实验结果证明,在太阳光和天然半导体矿物共同作用下,A.f.菌的对数生长期由无光时的36 h延长到72 h,同时细菌的生长在该能量转化过程中得到了明显促进.在天然闪锌矿催化条件下,有光条件的A.f.菌数量增加到无光条件的1.90倍;而在金红石催化条件下,有光条件的A.f.菌数量增加到无光条件的1.69倍.实验结果说明,在以天然半导体矿物为媒介的情况下,化能自养微生物可间接利用太阳能来获得自身的生长繁殖所需的能量,这一过程也实现了太阳光能→电能→化学能→生物质能的能量转化途径.     

矿物光电子-微生物体系重金属离子价态调控及其环境效应研究进展

本文综述了典型污染区重金属离子赋存状态与环境风险评价、环境微生物多样性等环境质量因子的关系及其对土壤功能的影响;重点介绍了微生物源电子、半导体矿物光电子对重金属离子的价态调节双向控制;总结了电子穿梭体、空穴捕获剂等小分子有机物对光电子还原重金属离子的影响及机制,以及半导体矿物光电子、重金属价电子协同微生物对重金属离子的还原氧化效率与价态调控;分析了微生物及其表面基团对重金属离子的矿化与转化作用,以及微生物界面固定转化在土壤重金属污染修复中的作用。本综述可为进一步研究微生物和半导体矿物光电子协同作用对重金属离子的定向调节、电子转移途径、晶相转化机制提供指导,对深入探讨光-半导体矿物-重金属离子-微生物多相复杂体系的交互作用具有重要的环境学意义。     

关键带中天然半导体矿物光电子的产生与作用

在地球上最不均匀和最复杂的区域——关键带这一极为复杂的开放系统中,矿物与微生物无时无刻不在发生着人们尚未充分认识到的自然作用。文中总结了作者十余年来在矿物与微生物交互作用研究领域,侧重在半导体矿物与微生物协同作用研究方向上所取得的研究成果,重点简述了自然界中半导体矿物特征、半导体矿物光电子特性、矿物光电子促进生命起源与演化、微生物利用矿物光电子——光电能微生物的发现以及土壤矿物光电子与微生物协同固碳作用等研究工作。矿物与微生物之间电子转移和能量流动是关键带中最为重要的动力机制之一,探讨关键带中大量存在的天然半导体矿物如何转化太阳能为化学能或者生物质能的微观作用,可为揭示关键带中多个圈层之间交互作用如何影响地球物质演化、生物进化与环境演变的宏观过程提供理论依据,充满着科学发现与理论突破的机遇。     

地表“矿物膜”半导体矿物光电子调控微生物群落结构演化特性研究

矿物-微生物交互作用广泛参与地球表层系统物质循环与能量流动过程,深刻地影响着一系列重要的地表生物地球化学进程。近年来地表半导体矿物的相关研究,为矿物-微生物交互作用提供了崭新研究方向,揭示地表“日光-半导体矿物-微生物”系统电子传递过程及其环境效应,是地质微生物学交叉领域研究的核心科学问题之一。本研究从地表不同生境“矿物膜”出发,以光电化学技术证实喀斯特、红壤、岩石漆“矿物膜”在1 000 min长时间循环实验中平均光电流值约为5.4、3.4、3.2 μA/cm²,证实“矿物膜”良好日光响应特性且铁锰氧化物矿物在其中发挥核心作用。基于笔者前期研究所发现的“矿物膜”电活性菌富集且与半导体矿物分布呈正相关性这一现象,本文进一步构建模拟光电子红壤细菌群落系统,20天后细菌群落α多样性显著提升,研究证实细菌群落具有模拟光电子响应活性,且电极与溶液群落均具有演化方向性;16S rRNA测序分析表明模拟光电子作用下Shewanella、Pseudomonas、Streptococcus、Lactobacillus、Acinetobacter等电活性菌显著富集。综上,本文研究结果间接证实地表半导体矿物光电子可有效调控微生物群落结构并促进电活性菌在“矿物膜”中富集。     

微生物还原铁氧化物矿物的电化学研究

微生物可以还原铁氧化物矿物。本文通过使用电化学方法对铁氧化物矿物在微生物还原作用下的氧化还原特性进行模拟与表征,补充了从新角度对微生物还原铁氧化物矿物的研究。研究结果显示,微生物可直接以铁氧化物矿物作为电子受体将其还原得到二价铁生成物。电化学实验显示,0.2 mA阴极恒电流条件下铁氧化物矿物可以接受电子,同时铁氧化物矿物中的Fe3+在0.89±0.01 V(相对于饱和甘汞电极)时发生还原反应,表明铁氧化物矿物满足被微生物还原的电化学条件。双室微生物-铁氧化物矿物体系研究证实,铁氧化物矿物可以作为阴极接受微生物提供的电子。     

几种锰氧化物矿物能带结构研究

锰氧化物是常见的半导体材料之一,本文利用XRD、Raman、X射线吸收-发射谱及Zeta电位测试技术对合成的4种锰氧化物矿物(酸性水钠锰矿、碱性水钠锰矿、δ-MnO_2、锰钾矿)的能带结构进行了理论计算。结果表明,4种矿物均是可见光响应的半导体矿物,其禁带宽度分别为2.32 eV、1.77 eV、1.36 eV、1.23 eV;在p H等于6时,4种锰氧化物矿物对应的导带电势分别为-0.32 V、0.09 V、0.39 V、0.46 V(vs.NHE),价带电势分别为2.00 V、1.86 V、1.75 V、1.69 V(vs.NHE)。与腐殖质氧化还原电势相比较,4种锰氧化物矿物在任何pH条件下均能吸收可见光催化氧化腐殖质。从结构上比较,层状结构比隧道结构的锰氧化物可见光催化氧化还原能力更强。     

针铁矿为填料的反硝化生物滤池的启动及运行

随着我国经济的发展和城市化进程的加快,日均产生的各种工业废水和生活污水也在增加。我国目前城市污水处理厂的出水普遍能够达到一级B标准,然而其中的总氮浓度依然是湖泊水体二类标准的10倍甚至更多。污水处理厂出水中的总氮主要是以硝态氮的形式存在,因此,我国的部分天然水体中面临着严重的硝酸盐污染的风险。另一方面,我国北方部分地区长期饮用含有高硝酸盐的地下水,某些地区的地下水中硝酸盐含量高达392 mg·L-1,远超过世界卫生组织规定的10 mg·L-1。鉴于此,为了保障饮水安全,亟需发展反硝化脱氮的污水深度处理技术。反硝化生物滤池(denitrification biofilter,DNBF)是一种由曝气生物滤池(BAF)演化而来用于处理污水中氮素污染的新型工艺,其具有占地小、出水水质好、抗冲击负荷强、快速启动、生物量大、处理效率高等优点。填料是影响DNBF运行及反硝化处理效果的重要因素之一。常规的DNBF填料有火山岩、陶粒、沸石、石英砂等。课题组近几年系统研究了天然针铁矿在有机物厌氧消化及C、N等元素的生物地球化学过程中的作用,前期研究结果表明天然针铁矿可以提高生物反硝化的速率和效率。因此,本文以石英砂为对照,探索DNBF在以天然针铁矿作为填料时的反硝化效果,并具体分析了两个DNBF在启动和稳定运行阶段的性能差异。实验装置采用实验室规模的上流式连续流反应器,有效容积为1.2 L。整个装置的接口处均用硅胶密封。反应器运行的控制参数为:进水p H 7.50±0.15(通过0.1 mol·L-1 HCL调节),C/N为4,水力停留时间(hydraulic retention time,HRT)为4和2 h,当HRT为4 h时反应器氮容积负荷(以N计,下同)保持在0.6 kg·(m3·d)-1。本研究采用人工接种挂膜法,接种污泥采用实验室培养驯化的反硝化污泥。每天采样,分析测定两个反应器启动阶段以及不同HRT运行阶段时的进出水中的化学需氧量(chemical oxygen demand,COD)、NO-3、NO-2等指标。DNBF启动运行阶段HRT设为4 h时,以针铁矿和石英为填料的DNBF分别在第8天时和第15天时进入稳定运行状态,COD的去除率在84%~85%,NO-3的去除率均为99%。实验结果表明DNBF反应器以针铁矿为填料,能够缩短反应器的启动时间。这可能是因为天然针铁矿颗粒表面粗糙,比表面积更大,有利于微生物附着生长,因此反应器的启动时间更短。在DNBF稳定运行阶段,当HRT为4 h时,针铁矿为填料的DNBF对COD和NO-3的去除率约为85.45%±0.65%和99.17%±0.11%,石英砂为填料的反应器对COD和NO-3的去除率约为84.56%±0.79%和99%±0.12%,两种填料的反应器的反硝化效果区别不大;当HRT降为2 h并连续运行10 d后,以针铁矿为填料的DNBF对COD和NO-3的去除率分别为84.98%和99.48%,以石英砂为填料的DNBF对COD和NO--3的去除率分别为74.01%和84.51%,且以石英砂为填料的DNBF中出现了NO2的积累,最大积累量达到0.6 mg/L。实验结果表明,针铁矿为填料的DNBF有更好的抗冲击负荷的能力,且不易产生亚硝酸盐氮的累积。引起上述实验现象的原因之一是由于天然针铁矿中含有铁以及其他的一些微量金属元素,当三价铁被还原为微生物可利用的二价铁时,其他金属元素也随之释放到滤池中用作微生物的营养物质。因此,以针铁矿为填料的DNBF中的生物量较多,反硝化菌活性较高。针铁矿促进反硝化过程的具体机制还有待进一步的深入研究。     

Semiconducting Mineral Photocatalytic Regeneration of Fe2+ Promotes Carbon Dioxide Acquisition by Acidithiobacillus ferrooxidans

Chemoautotrophic organisms have once been excluded from the development of universally applicable CO2 fixation technology due to its low production yields of biomass. In this study, we used Acidithiobacillus ferrooxidans (A.f.) as a model chemoautotrophic microorganism to test the hypothesis that exogenetic photoelectrons from semiconducting mineral photocatalysis can enable the regeneration of Fe2+ that could be then used by A.f. and support its growth. In a simulated electrochemical system, where exogenetic electrons were provided by an electrochemical approach, an accelerated growth rate of A.f. was observed as compared with that in traditional batch cultivation. In a coupled system, where light-irradiated natural rutile provided the primary electron source to feed A.f., the bacterial growth rate as well as the subsequent CO2 fixation rate was demonstrated to be in a light-dependent manner. The sustaining flow of photogenerated electrons from semiconducting mineral to bacteria provided an inexhaustible electron source for chemoautotrophic bacteria growth and CO2 fixation. This finding might contribute to the development of novel effective CO2 fixation technology.     

Microbiological denitrification and denitrifying activity ofParacoccus Denitrificans

With rapidly industrial and agricultural development,more and more fertilizers,chemicals and heavy ions will be discharged into lakes and rivers,which would cause lake eutrophication and quality deterioration in drinking water sources.Therefore,denitrification is essential for controlling the amounts of nitrogen,During the transformation process from nitrate to the end products-nitrogen and several intermediated[e.g.nitrite(NO2^-),nitrous oxide(N2O) and nitric oxide(NO)]may be accumulated,which have more toxic influences on the environment.in This study,the denitrification effect of Paracoccus Denitrificans was examined on the changes between oxic and anoxic conditions at varying pH.At pH=7.5,denitrification proceeded well after 3 switches from oxic to anoxic conditions and vice versa,Production of N2 was constant and the amounts of NO2-,N2O and NO were extremely low.How ever,at pH=6.8,denitrification activity was inhitied and there large amounts of the intermaediates.The denitrifying bacteria decreased violently in dry weight and were washed out.     

Surface potential and dixanthogen stability on chalcopyrite surface

Contact angle measurements, ultraviolet (UV) spectroscopy and voltammetry were used in this investigation to study the effect of various externally applied potentials on the stability of dixanthogen at synthetic and natural chalcopyrite surfaces.The results of contact angle measurements indicate that synthetic and natural chalcopyrites have similar wettabilities. Their hydrophobic potential range in a 7 × 10^− 4 M PAX solution was + 0.04 V to + 0.44 V vs. NHE at pH 10 and was − 0.01 V to + 0.54 V at pH 7.UV spectroscopic results show that dixanthogen began to form on the chalcopyrite surface at a potential of + 0.04 V vs. NHE at pH 10 and − 0.01 V vs. NHE at pH 7. The amount of dixanthogen formed on the chalcopyrite surface initially increased with the increase of the applied potential and then decreased with the increasing potential. The optimum potential range for dixanthogen formation on the chalcopyrite surface was from + 0.14 V to + 0.34 V vs. NHE at pH 10 and from + 0.14 V to + 0.44 V vs. NHE at pH 7. It was difficult to completely remove the dixanthogen film on the chalcopyrite surface.     

Electrokinetic Stabilization of Soft Soil Using Carbonate-Producing Bacteria

The carbonate (CO ₃ ^?2 ) produced by Sporosarcina pasteurii was injected electrokinetically to enhance the mechanical properties of soft clay soils. In this method the Ca²⁺ was injected into the anode chamber and moved towards the cathode by electromigration and electroosmotic flow. Then the released CO ₃ ^?2 from a blend of bacteria and urea was injected into the cathode chamber. The CO ₃ ^?2 ions were moved from the cathode to the anode under electromigration mechanism. The CaCO₃ was precipitated in the presence of calcium in porous medium of the soil, and consequently increased the shear strength of the soil. The polarity reversal was applied to have a homogeneous distribution of CaCO₃.     

Oyster (<Emphasis Type="Italic">Crassostrea virginica</Emphasis>) Aquaculture Shifts Sediment Nitrogen Processes toward Mineralization over Denitrification

Filter-feeding bivalves, like oysters, couple pelagic primary production with benthic microbial processes by consuming plankton from the water column and depositing unassimilated material on sediment. Conceptual models suggest that at low to moderate oyster densities, this deposition can stimulate benthic denitrification by providing denitrifying bacteria with organic carbon and nitrogen (N). While enhanced denitrification has been found at oyster reefs, data from oyster aquaculture are limited and equivocal. This study measured seasonal rates of denitrification, as well as dissimilatory nitrate reduction to ammonium (DNRA), and dissolved inorganic N fluxes at a rack and bag eastern oyster (Crassostrea virginica) aquaculture farm. Consistent with models, denitrification was enhanced within the farm, with an average annual increase of 350% compared to a reference site. However, absolute denitrification rates were low relative to other coastal systems, reaching a maximum of 19.2 μmol m^?2 h^?1. Denitrification appeared to be nitrate (NO₃ ^?) limited, likely due to inhibited nitrification caused by sediment anoxia. Denitrification may also have been limited by competition for NO₃ ^? with DNRA, which accounted for an average of 76% of NO₃ ^? reduction. Consequently, direct release of ammonium (NH₄ ⁺) from mineralization to the water column was the most significant benthic N pathway, with seasonal rates exceeding 900 μmol m^?2 h^?1 within the farm. The enhanced N processes were spatially limited however, with significantly higher rates directly under oysters, compared to in between oyster racks. For commercial aquaculture farms like this, with moderate oyster densities (100–200 oysters m^?2), denitrification may be enhanced, but nonetheless limited by biodeposition-induced sediment anoxia. The resulting shift in the sediment N balance toward processes that regenerate reactive N to the water column rather than remove N is an important consideration for water quality.     

Benthic nitrogen cycling traversing the Peruvian oxygen minimum zone

Benthic nitrogen (N) cycling was investigated at six stations along a transect traversing the Peruvian oxygen minimum zone (OMZ) at 11°S. An extensive dataset including porewater concentration profiles and in situ benthic fluxes of nitrate (NO₃⁻), nitrite (NO₂⁻) and ammonium (NH₄⁺) was used to constrain a 1-D reaction-transport model designed to simulate and interpret the measured data at each station. Simulated rates of nitrification, denitrification, anammox and dissimilatory nitrate reduction to ammonium (DNRA) by filamentous large sulfur bacteria (e.g. Beggiatoa and Thioploca) were highly variable throughout the OMZ yet clear trends were discernible. On the shelf and upper slope (80-260 m water depth) where extensive areas of bacterial mats were present, DNRA dominated total N turnover (?2.9 mmol N m⁻² d⁻¹) and accounted for ?65% of NO₃⁻ + NO₂⁻ uptake by the sediments from the bottom water. Nonetheless, these sediments did not represent a major sink for dissolved inorganic nitrogen (DIN = NO₃⁻ + NO₂⁻ + NH₄⁺) since DNRA reduces NO₃⁻ and, potentially NO₂⁻, to NH₄⁺. Consequently, the shelf and upper slope sediments were recycling sites for DIN due to relatively low rates of denitrification and high rates of ammonium release from DNRA and ammonification of organic matter. This finding contrasts with the current opinion that sediments underlying OMZs are a strong sink for DIN. Only at greater water depths (300-1000 m) did the sediments become a net sink for DIN. Here, denitrification was the major process (?2 mmol N m⁻² d⁻¹) and removed 55-73% of NO₃⁻ and NO₂⁻ taken up by the sediments, with DNRA and anammox accounting for the remaining fraction. Anammox was of minor importance on the shelf and upper slope yet contributed up to 62% to total N₂ production at the 1000 m station. The results indicate that the partitioning of oxidized N (NO₃⁻, NO₂⁻) into DNRA or denitrification is a key factor determining the role of marine sediments as DIN sinks or recycling sites. Consequently, high measured benthic uptake rates of oxidized N within OMZs do not necessarily indicate a loss of fixed N from the marine environment.     

不同温度条件下氨氮在砂土中的吸附实验研究

温度的变化能够改变水体的环境,引起周围环境中的离子吸附解吸作用的变化。不同于其他土壤,砂土的保水保肥能力更差,砂土地区一旦发生氨氮(NH₄⁺-N)污染,情况会更加严重和突出。为防治砂土地区N H₄⁺-N污染提供理论依据与技术支持,通过N H₄⁺-N的静态吸附试验,研究不同温度条件下N H₄⁺N在粗砂、中砂、细砂中的吸附转化特征,得到如下结论: 在试验设置的温度区间内,总的趋势是温度越低,砂土对N H₄⁺-N的吸附量越高,表明温度升高对N H₄⁺-N的吸附有抑制作用,这主要是因为吸附过程中会产生弱放热效应,进而降低渗滤介质对N H₄⁺N的平衡吸附量; 在25~30 ℃区间内存在硝化与反硝化作用的临界温度,当温度低于临界温度时,N H₄⁺-N吸附量的减少主要是由于发生了硝化反应,当温度高于临界温度时,N H₄⁺-N的吸附量减少主要是由于发生了反硝化反应。     

Preparation and characterization of antibacterial silver/vermiculites and silver/montmorillonites

The reason for the preparation and characterization of the novel antibacterial silver/vermiculites (Ag/V) together with the silver/montmorillonites (Ag/M) was that the information on the vermiculite structure change and stability of Ag/V in water as well as its effect on bacteria are sporadic. The vermiculite (V), (Si_3.02Al_0.98)^IV (Mg_2.27Al_0.12Ti_0.07)^VI O₁₀(OH)₂ Ca_0.09Na_0.21K_0.50 from West China and montmorillonite (M), (Si_3.96Al_0.04)^IV (Al_1.20Mg_0.42Ti_0.02)^VI O₁₀ (OH)₂Ca_0.15Na_0.14K_0.08 from Ivan?ice (Czech Republic), fraction <0.4 μm were the starting clay materials for sample preparation. The samples V1 and M1 were prepared via reaction of the V and M with the 0.01 mol L⁻¹ AgNO₃ aqueous solution. The samples V2 and M2 were treated with the aqueous solution of AgNO₃ for two times. The cation exchange and reduced metallic silver on M1 and V1 evoked the specific surface area (SSA) diminution, the mean particle-size diameter extension and appearance of micropores with radius (<0.4 nm). Repeated silver cation exchange in M2 and V2 reduced particle size, increased slightly SSA and micropores with radius of 0.4-0.5 nm. Samples Ag/V and Ag/M showed higher content of pores with radius 0.5-1.0 nm than original V and M. The Ag concentration was found higher in Ag/V than in Ag/M and higher in repeatedly treated samples: 0.9 wt.% Ag in V1, 1.4 wt.% Ag in V2, 0.6 wt.% Ag in M1 and 1.0 wt.% Ag in M2. Vermiculite structure consisting of the hydrated interstratified phases and the mica-like phase changed to the cation-one-zero layer hydrate interstratification structure in V1 and to the random of two-one layer hydrate interstratifications in V2. Infrared and Mössbauer spectroscopy revealed no changes in the structure of the clay minerals that could be related directly to the sorption and crystallization of silver. Transmission electron microscopy showed that the silver nanoparticles size distribution was much narrower for the samples Ag/M than for Ag/V. The mean size of the Ag particles was between 40 and 50 nm. Although the Ag nanoparticles did not adhere sufficiently at the clay minerals surface and migrated moderately into water, all samples under study were approved to be effective inhibitors of the bacterial growth persisting for the whole testing period of 6 days. Silver/vermiculite was antimicrobial more efficient against Klebsiella pneumoniae and Pseudomonas aeruginosa than silver/montmorillonite.     

The distribution of nitrate N/N in marine sediments and the impact of benthic nitrogen loss on the isotopic composition of oceanic nitrate

We report ¹⁵N/¹⁴N ratios of porewater nitrate in sediments from the Bering Sea basin, where microbial nitrate reduction has been identified as a significant sink for fixed nitrogen (N). Strong ¹⁵N enrichment in porewater nitrate is observed as one goes deeper in the sediments and nitrate concentration decreases (δ¹⁵N generally reaches 25-35‰). Analysis of profiles with a one-dimensional diffusion-reaction model yields organism-scale isotope effects for dissimilatory nitrate reduction (ε_cell) of 11‰ to 30‰, in the same range as measured in previous studies of cultures and the marine and lacustrine water column. Estimates of ε_cell, while uncertain, show a negative correlation with bottom water [O₂]; we propose that this relates to the at the depth of denitrification. The N isotope effect at the scale of nitrate sediment-water exchange (ε_app) is ∼0‰ in two unreactive deep sites and is typically <3‰ at more reactive sites at various depths. ε_app is much lower than ε_cell because nitrate consumption is nearly complete at the sediment depth of denitrification, minimizing the escape of ¹⁵N-enriched nitrate from the sediments. In reactive sediments, this is due to rapid denitrification, while in less reactive sediments, it is due to greater diffusive distances for nitrate to the depth of denitrification. The data suggest that low bottom water [O₂] tends to yield more complete expression of ε_cell at the sediment-water scale, due to higher at the depth of denitrification. While porewater ammonium-N isotopes were not measured, our porewater model suggests that, in sediments with high organic matter supply and/or low-[O₂] bottom waters, the efflux and subsequent oxidation of ammonium enriched in ¹⁵N by incomplete nitrification can significantly enhance the total net isotope effect of sedimentary N loss (ε_sed, equivalent to ε_app but including ammonium fluxes). Model analysis of representative sedimentary environments suggests a global mean ε_sed of ∼4‰ (∼2‰ if restricted to seafloor below 1 km depth).