厌氧氨氧化菌富集培养物对羟胺的转化研究

【目的】羟胺是厌氧氨氧化的重要中间产物,本研究旨在探明厌氧氨氧化菌对羟胺的转化特性。【方法】采用厌氧氨氧化菌富集培养物,以羟胺和亚硝酸盐为基质进行分批培养试验,检测反应液中基质和产物的消涨情况。【结果】不接种厌氧氨氧化富集培养物时,羟胺和亚硝酸盐具有化学稳定性,彼此不发生化学反应;接种厌氧氨氧化富集培养物后,羟胺和亚硝酸盐发生化学反应;反应过程中有中间产物氨的产生和转化,最大氨氮积累浓度为0.338mmol/L;液相中总氮浓度从起始的4.694mmol/L降至结束时的0.812mmol/L,转化率为82.7%。羟胺和亚硝氮浓度均为2.5mmol/L时,羟胺最大比污泥转化速率为0.535mmol/(gVSS.h),是厌氧氨氧化反应体系中氨氮最大比污泥转化速率的1.81倍。将羟胺浓度提高至5.0mmol/L时,羟胺和亚硝氮转化速率分别提高26.7%和120.7%,最大氨氮积累浓度为0.795mmol/L;将亚硝氮浓度提高至5.0mmol/L时,羟胺和亚硝氮转化速率分别提高6.9%和9.0%,最大氨氮积累浓度为1.810mmol/L。【结论】厌氧氨氧化富集培养物能够转化羟胺,其对羟胺的转化速率高于对氨的转化速率。羟胺相对过量可显著加快羟胺和亚硝酸盐的转化速率,亚硝酸盐相对过量对羟胺和亚硝氮转化速率影响不大,提高羟胺或亚硝氮浓度均会增大中间产物氨氮的积累。实验现象可用van de Graaf模型解释,对于进一步开发厌氧氨氧化工艺具有重要的理论意义。     

Pseudomonas alcaliphila AD-28的脱氮性能及其关键酶活性

【背景】异养硝化-好氧反硝化菌由于能够同时实现硝化反硝化作用而备受关注,但由于菌的种类不同,其脱氮途径不尽相同,研究菌株脱氮关键酶的种类及其活性可以推测菌株的脱氮途径,从而为菌株在生产上的应用提供技术支撑。【目的】研究Pseudomonas alcaliphila AD-28的脱氮性能及其关键酶的活性,为菌株脱氮分子机理研究奠定基础。【方法】以柠檬酸钠为碳源,以硫酸铵、亚硝酸钠、硝酸钾为氮源,研究菌株AD-28的脱氮性能并检测其关键酶氨单加氧酶(AMO)、羟胺氧化还原酶(HAO)、亚硝酸盐还原酶(NIR)、硝酸盐还原酶(NAR)的酶活性。【结果】菌株AD-28培养24h的菌密度(OD600)可达1.971,对初始浓度为18.85mg/L的氨氮、26.13mg/L的硝酸盐氮、19.47mg/L的亚硝酸盐氮、66.11 mg/L的总氮去除率均达到96%以上;关键酶AMO、HAO、NIR和NAR的比活力分别为0.028、0.003、0.011、0.027 U/mg。【结论】Pseudomonas alcaliphila AD-28能同时进行异养硝化-好养反硝化作用,该菌在AMO作用下将NH4+-N氧化为羟胺,然后由HAO氧化为NO2--N,NO2--N和NO3--N在NIR、NAR等酶的催化作用下脱氮。     

一株高效去除亚硝酸氮细菌的分离鉴定及其脱氮特性研究

【目的】从南美白对虾养殖塘中分离到高效去除亚硝酸氮的细菌, 对其分类和脱氮特性进行了研究。【方法】 以除亚硝酸氮为主要指标, 取养殖塘底层水样分离筛选菌株; 依据16S rRNA基因序列和生理生化特征初步鉴定菌株; 研究不同碳源、碳氮比、起始pH、温度、摇床转速和氯化钠浓度对反硝化除亚硝酸氮的影响, 并考查了菌株对硝酸氮和氨氮的利用情况。【结果】得到的菌株中菌株FP6活性最高, 初步鉴定菌株FP6属于地衣芽孢杆菌。菌株FP6的生长最适脱氮碳源为蔗糖, 菌株FP6去除亚硝酸氮有高活性的条件范围为: C/N值15?25、起始pH 7.0?10.0、温度20 °C?37 °C、摇床转速0?200 r/min和氯化钠浓度0?40 g/L。菌株FP6对硝酸氮和氨氮都有一定的去除能力, 利用硝酸氮时不积累亚硝酸氮。【结论】地衣芽孢杆菌FP6具有优良的除亚硝氮特性, 适宜的温度、pH和盐度范围较宽。     

好氧和缺氧条件下游离亚硝酸对氨氧化菌和亚硝酸盐氧化菌的选择性抑制

【背景】稳定短程硝化是实现城市污水厌氧氨氧化技术的瓶颈,目前国内外关于游离亚硝酸(Free nitrous acid,FNA)对硝化菌活性的影响大多是在曝气条件下进行研究,鲜有关于缺氧条件下FNA对硝化菌活性影响的报道。【目的】探究好氧和缺氧下FNA对氨氧化菌(Ammonia oxidizing bacteria,AOB)和亚硝酸盐氧化菌(Nitrite oxidizing bacteria,NOB:Nitrospira和Nitrobacter)活性的抑制影响。【方法】采用序批式反应器(Sequencing batch reactor,SBR),基于混合液悬浮固体浓度(Mixed liquid suspended solids,MLSS)为8 300 mg/L的全程硝化污泥条件,通过批次试验分别考察好氧和缺氧下FNA(初始浓度为1.16 mg/L)处理48 h后,AOB和NOB活性的变化情况。【结果】好氧FNA处理活性污泥48 h后,FNA浓度维持在1.16-1.17 mg/L,游离氨(Free ammonia,FA)浓度小于0.017 mg/L,AOB、Nitrospira、Nitrobacter丰度均未发生明显变化;过曝气至99 h时,与空白组相比,比氨氮氧化速率(r~+_(NH4-N))、比亚硝酸盐氮氧化速率(r_(NO2-N))均出现小幅下降,分别由3.5、4.828 mg N/(g VSS·h)降至3.3、4.668 mg N/(g VSS·h),且亚硝酸盐氮累积率(Nitrite accumulation rate,NAR)始终低于33.2%。缺氧FNA处理活性污泥48 h后,FNA浓度维持在0.64-1.16 mg/L,FA浓度低于0.039 mg/L,AOB丰度变化较小,而Nitrospira、Nitrobacter丰度均明显下降,分别由3.002 9×10~9、4.245×10~8 copies/g VSS降至1.666 5×10~8、5.163 8×10~7 copies/g VSS;过曝气至99 h时,与空白组相比,r~+_(NH4-N)值下降幅度较小,而r_(NO2-N)值明显降低,由4.828 mg N/(g VSS·h)降至0.007 mg N/(g VSS·h),且在过曝气0-292 h内,NAR均大于94%。【结论】好氧FNA处理活性污泥48 h后对AOB和NOB无明显抑制作用,但缺氧FNA处理活性污泥48 h后对AOB具有轻微抑制作用,而对NOB具有强烈的抑制作用,可以实现稳定的短程硝化。     

短程硝化启动运行中功能菌群变化研究

【目的】短程硝化-厌氧氨氧化是可实现的最短生物脱氮工艺,短程硝化是实现该工艺的重要环节和必要条件。【方法】采用序批式反应器(SBR)来实现短程硝化过程的启动和稳定运行,并对该过程中的相关功能菌群变化进行检测分析。【结果】通过控制低DO浓度(<1 mg/L)和逐步提高氨氮进水负荷,可抑制氨氧化细菌(NOB)菌群增殖并促进亚硝酸氧化菌(AOB)菌群规模显著扩大,实现短程硝化过程的启动和稳定运行。在氨氮进水负荷为0.055 kg/(m3.d)时,平均氨氮去除容积负荷和污泥负荷可达到0.043kg/(m3.d)和0.16 kg/(kg.d),平均亚硝酸盐积累率可达到83.4%。在短程硝化启动和稳定运行过程中,NOB菌群密度从2.0×105CFU/mL降至1.5×104CFU/mL,相对丰度从5.51%降至2.14%;AOB菌群密度从4.5×104CFU/mL增加至1.5×107CFU/mL,相对丰度从0.18%增加至7.25%。【结论】AOB菌群规模的扩大是实现短程硝化和氨氮去除能力提高的主要原因,同时较高的进水氨氮浓度和负荷也会造成亚硝化活性的抑制。     

反硝化除磷菌筛选及其特性研究

【目的】研究反硝化除磷菌特性。【方法】通过微生物筛选和生物学特性研究方法,从对虾养殖池塘中筛选出多株可在有氧条件下同时具有反硝化除磷功能的菌种。【结果】菌株LY-1可在18 h内将初始量为10 mg/L的亚硝酸盐氮降低至0.04 mg/L,PO43?-P降低至0.05 mg/L。在DO浓度为5.0?5.9 mg/L时,该菌反硝化除磷率近100%。试验选取具有反硝化除磷功能的枯草芽孢杆菌为阳性对照菌,大肠杆菌为阴性对照菌,比较研究了菌株LY-1在不同pH、温度、盐度、PO43?-P浓度、亚硝酸盐浓度时反硝化除磷的强弱,在pH为5?9范围时,该菌亚硝酸盐氮去除率近99%,PO43?-P去除率86%;温度为30°C时,该菌反硝化除磷率近100%;盐度为5‰?15‰、PO43?-P浓度为10 mg/L、亚硝酸盐氮浓度为20 mg/L时,该菌亚硝酸盐氮和PO43?-P去除率均可达99%。【结论】菌株LY-1反硝化除磷性能显著高于对照菌(P<0.05)。通过菌株LY-1形态学观察、生理生化及16S rRNA基因序列分析,初步鉴定为蜡样芽孢杆菌(Bacillus cereus)。     

一株海洋好氧反硝化细菌的鉴定及其好氧反硝化特性

【目的】从处理海洋养殖循环水的生物滤器生物膜中分离到1株具有好氧反硝化活性的细菌(菌株2-8),并进一步研究了该菌的分类地位及反硝化特性。【方法】采用16S rRNA基因序列分析对菌株进行初步鉴定,采用好氧培养技术,探讨了碳源种类、起始pH、NaCl浓度、C/N、温度和摇床转速对菌株2-8好氧反硝化活性的影响。【结果】该菌株的16S rRNA基因序列与Pseudomonas segetis FR1439T(AY770691)的相似性最高,达到99.9%,因此初步鉴定菌株2-8属于假单胞菌属(Pseudomonas sp.2-8)。碳源类型和C/N对其好氧反硝化作用的影响最为显著,以柠檬酸钠为唯一碳源,C/N为15时脱氮效率最高,低C/N导致亚硝酸盐的积累;其好氧反硝化的最适温度和pH分别为30℃和7.5;菌株2-8在摇床转速为160r/min下脱氮效果最好;NaCl浓度对其反硝化活性的影响不明显。【结论】在初始硝酸氮浓度为140mg/L,以柠檬酸钠为唯一碳源、C/N为15、pH为7.5、NaCl浓度为30g/L,30℃以及160r/min摇床培养的条件下,菌株2-8在48h内脱氮率可达92%且无亚硝酸盐积累。     

耐碱反硝化菌株的分离鉴定与功能检测

【目的】分离获得耐碱反硝化菌株,确定其反硝化活性和耐碱能力。【方法】分离、纯化,获得耐碱反硝化菌株;通过形态观察、生理生化试验和16S rRNA基因测序分析,确定菌株分类地位;试验起始硝酸盐浓度和起始pH对分离菌株反硝化活性的影响。【结果】从实验室稳定运行的高效反硝化反应器中分离获得耐碱反硝化菌株R9,经鉴定归于Diaphorobater nitroreducens;菌株R9能够以甲醇为电子供体、硝酸盐为电子受体进行异养生长,当起始硝氮浓度为50 mg/L、起始pH为9.0时,288 h内硝氮去除率达93.25%;高浓度硝氮可抑制其反硝化活性,半抑制常数Ki为202.73 mg N/L;菌株R9的耐碱性良好,起始pH为11.0时的硝氮去除率是pH为9.0时的86%。【结论】菌株R9归于Diaphorobater nitroreducens,最适生长pH为9.0左右,是一株耐碱反硝化菌。     

Mn2+对A/O-BAF系统处理效能和细菌群落多样性的影响

【目的】通过考察Mn²⁺对A/O-BAF系统处理效能及微生物群落多样性的影响,研究了15℃下不同浓度Mn²⁺对A/O-BAF系统处理效能的影响,并通过高通量测序考察了细菌群落多样性的变化情况。【方法】在温度15℃、水力负荷0.50 m3/(m2·h)、气水比10:1的条件下,在进水中投加Mn²⁺,考察反应器处理效能的变化情况,并通过高通量测序对BAF生物膜样品进行分析。【结果】2.0 mg/L Mn²⁺作用下A/O-BAF系统的COD、NH4+-N、TN、TP去除率分别提高3.51%、2.21%、6.26%和12.13%;4.0 mg/L Mn²⁺作用下COD、NH4+-N、TN、TP去除率分别提高了4.24%、1.92%、7.75%和10.73%;Mn²⁺作用下A/O-BAF系统内反硝化细菌和亚硝酸菌的数量明显增加,硝酸菌数量有所减少,生物膜量和生物膜活性提高。高通量测序结果可知:2.0 mg/L和4.0 mg/L Mn²⁺作用下,微生物群落多样性大幅增加,样本OTU数量从4430分别提高到5659和5556;BAF柱内变形菌门(Proteobacteria)、厚壁菌门(Firmicutes)、黄色单胞菌科(Xanthomonas)、红环菌科(Rhodocyclaceae)、丛毛单胞菌科(Comamonadacea)、丛毛单胞菌属(Comamonas)、陶厄式菌属(Thauera)、Denitratisoma、Sulfuritalea和热单胞菌属(Thermomonas)的相对丰度增加。部分微生物丰度[例如Denitratisoma、Sulfuritalea、红环菌科(Rhodocyclaceae)和丛毛单胞菌科(Comamonadacea)]的增加幅度随着Mn²⁺浓度的提高有所减少;Mn²⁺作用下硝化螺旋菌门(Nitrospirae)和硝化螺菌属(Nitrosospira)的相对丰度减少。【结论】一定浓度下Mn²⁺主要是通过促进A/O-BAF系统的亚硝化和反硝化作用和除磷微生物的生长提高A/O-BAF系统污染物去除效果,但对硝化的促进效果并不明显,且硝酸菌更易被Mn²⁺的抑制和毒害作用所影响。     

发光细菌JMU07的分离鉴定及其在生物毒性测定的初步研究

从乌贼表皮通过分离纯化得到一株发光细菌JMU07。该菌的菌落形态呈典型细菌菌落特征;显微镜下观察其为球杆状菌,革兰氏染色阴性。用荧光分光光度计测定其发光波长在420-650 nm之间,最大发光波长为477 nm。16S rDNA法测序,构建系统进化树,初步鉴定发光细菌JMU07为鳆发光杆菌(Photobacterium leiog-nathi)。生长发光曲线测定表明,发光细菌JMU07发光强度最高出现在对数中后期,相比明亮发光杆菌,JMU07具有发光强度高,持续发光时间长的特点。根据国标GB/T15441-1995研究HgCl2浓度与发光细菌JMU07发光强度抑制率的关系得到:HgCl2浓度与发光细菌JMU07发光强度抑制呈良好线性关系;JMU07 EC50为0.11 mg/L,略低于明亮发光杆菌的0.14 mg/L,表明JMU07对HgCl2的毒性更敏感。因此新分离得到的发光细菌JMU07有希望用于环境检测、食品卫生与安全等领域综合毒性的快速检测。     

Heterotrophic Nitrification by Arthrobacter sp

Arthrobacter sp. isolated from sewage oxidized ammonium to hydroxylamine, a bound hydroxylamine compound, a hydroxamic acid, a substance presumed to be a primary nitro compound, nitrite, and nitrate. The concentration of free hydroxylamine-nitrogen reached 15 mug/ml. The identification of hydroxylamine was verified by mass spectrometric analysis of its benzophenone oxime derivative. The bound hydroxylamine was tentatively identified as 1-nitrosoethanol on the basis of its mass spectrum, chemical reactions, and infrared and ultraviolet spectra. Hydroxylamine formation by growing cells was relatively independent of pH, but the accumulation of nitrite was strongly favored in alkaline solutions. The formation of hydroxylamine but not nitrite was regulated by the carbon to nitrogen ratio of the medium. The hydroxamic acid was the dominant product of nitrification in iron-deficient media, but hydroxylamine, nitrite, and 1-nitrosoethanol formation was favored in iron-rich solutions. Heterotrophic nitrification by Arthrobacter sp. was not inhibited by several compounds at concentrations which totally inhibited autotrophic nitrification.     

Heterotrophic nitrification and aerobic denitrification inAlcaligenes faecalis strain TUD

Heterotrophic nitrification and aerobic and anaerobic denitrification byAlcaligenes faecalis strain TUD were studied in continuous cultures under various environmental conditions. Both nitrification and denitrification activities increased with the dilution rate. At dissolved oxygen concentrations above 46% air saturation, hydroxylamine, nitrite and nitrate accumulated, indicating that both the nitrification and denitrification were less efficient. The overall nitrification activity was, however, essentially unaffected by the oxygen concentration. The nitrification rate increased with increasing ammonia concentration, but was lower in the presence of nitrate or nitrite. When present, hydroxylamine, was nitrified preferentially. Relatively low concentrations of acetate caused substrate inhibition (K_I=109 M acetate). Denitrifying or assimilatory nitrate reductases were not detected, and the copper nitrite reductase, rather than cytochrome cd, was present. Thiosulphate (a potential inhibitor of heterotrophic nitrification) was oxidized byA. faecalis strain TUD, with a maximum oxygen uptake rate of 140–170nmol O₂·min^-1·mg prot^-1. Comparison of the behaviour ofA. faecalis TUD with that of other bacteria capable of heterotrophic nitrification and aerobic denitrification established that the response of these organisms to environmental parameters is not uniform. Similarities were found in their responses to dissolved oxygen concentrations, growth rate and ammonia concentration. However, they differed in their responses to externally supplied nitrite and nitrate.     

沼泽红假单胞菌(Rhodopseudomonas palustris)CQV97对无机三态氮共存水体中氮素的去除效率及其影响因素

研究水体环境因素(温度、光照和pH)、小分子有机碳和有机氮化合物对一株具有高效脱氮潜力的沼泽红假单胞菌(Rhodopseudomonas palustris)CQV97在无机三态氮共存体系中脱除无机三态氮的影响规律。结果显示,该菌株在20~40℃,500~5 000lux,pH 6.0~9.0环境条件下,能够脱除高浓度无机三态氮(其中亚硝氮不低于40mg·L-1),表明该菌株具有较强的适应复杂环境的能力;以乙酸钠/乙醇为唯一碳源时,该菌株能有效地去除无机三态氮,而以葡萄糖为唯一碳源时,能有效去除硝氮,但不能去除氨氮,亚硝氮明显积累,表明环境中小分子有机碳源影响菌体对无机三态氮的去除能力;体系中添加高浓度(120mg·L-1)蛋白胨或尿素时,由于有机氮降解的释氨作用,菌体对氨氮的去除能力受到明显抑制,氨氮积累明显,13d时氨氮去除率仅分别为16%(蛋白胨)和6%(尿素),但硝氮和亚硝氮的去除能力并没有受到明显影响。异位处理实际水体结果表明,菌株可使水体中氨氮含量明显降低、硝氮和亚硝氮被完全去除。综上,沼泽红假单胞菌CQV97菌株环境适应能力强,具有高效脱除水体无机三态氮的应用潜力,这为进一步开发高效脱氮微生物制剂及其合理使用奠定了基础。     

Heterotrophic nitrification by Arthrobacter sp. (strain 9006) as influenced by different cultural conditions,growth state and acetate metabolism

An Arthrobacter sp. (strain 9006), isolated from lake water, accumulated nitrite up to about 15 mg N/l, but no nitrate. In a mineral medium supplemented with tryptone, yeast extract, acetate and ammonium, the cells released nitrite into the medium parallel to growth or when growth had virtually ceased. The nitrite formed was proportional to the initial acetate concentration, indicating an involvement of acetate metabolism with nitrification. The organism grew with a wide variety of organic carbon sources, but washed cells formed nitrite from ammonium only in the presence of citrate, malate, acetate or ethanol. Magnesium ions were required for nitrification of ammonium and could not be replaced by other divalent metal ions. Analysis of the glyoxylate cycle key enzymes in washed suspensions incubated in a minimal medium revealed that isocitrate lyase and malate synthase were most active during the nitrification phase. Nitrite accumulation but not growth was inhibited by glucose, tryptone and yeast extract. A possible explanation for the different nitrification patterns during growth is based on the regulatory properties of glyoxylate cycle enzymes.Abbreviations IL Isocitrate lyase [threo-D_s-isocitrate glyoxylate-lase, E.C. 4.1.3.1.] - MS malate synthase [l-malate glyoxylate-lyase (CoA-acetylating), E.C. 4.1.3.2.]     

Effects of Organic Acids on Heterotrophic Nitrification by Alcaligenes faecalis OKK17

Factors affecting heterotrophic nitrification by Alcaligenes faecalis OKK17, which was isolated from sewage sludge, were examined. Specific nitrifying activity increased as the pH increased up to 8.5. Most of the nitrogenous compounds (88%) in the culture supernatant were converted to hydroxylamine or nitrite at pH 9 but 87% of them remained as ammonium at pH 7. These results imply that the substrate for heterotrophic nitrification is ammonium and that the organism oxidizes ammonium to lower its toxic effect. Although the addition of acetate to a defined medium increased growth of the bacterium up to C/N = ca. 6, the accumulation of nitrification products almost paralleled the growth and the specific nitrifying activity decreased. Pyruvate and oxaloacetate increased the specific nitrifying activity six- to eightfold compared with the other organic acids examined, but the key enzyme activities in the glyoxylate cycle were not increased. Acetate, glyoxylate, and malonate did not increase the specific nitrifying activity, but they increased the enzyme activities. These results imply that the involvement of acetate metabolism in the heterotrophic nitrification is unlikely.     

Analyzing nitrogen and sulphide elimination from leachate by coulometric continuous flow titration

The process of leachate denitrification by populations of nitrifying and denitrifying bacteria was investigated. Leachate, derived from a local municipal landfill site, was nitrified in a continuously operating packed-bed biofilm reactor and thereafter denitrified in an activated sludge bioreactor. To follow the progress of nitrogen elimination, ammonium, nitrite and nitrate concentrations were determined at all stages of the process. While the nitrite and nitrate concentrations were measured by conventional colorimetric methods, computer controlled coulometric titration with in situ generated hypobromite was used for ammonium determination, which had previously been selectively separated from the sample matrix by gas dialysis. The detection range of the method was from 1 × 10^?6 to 1 × 10^?3 M ammonium (relative standard deviation (RSD) = 2%, n = 6). No interference of the complex sample matrix was found in ammonium determination. The average ammonium concentration in the leachate was 409 mg/l (standard deviation (SD) = 142 mg/l, n = 55). The ammonium concentrations decreased to 1–5 mg/l during nitrification under continuous operating conditions. Increased ammonium concentrations after nitrification correlated with a decrease in the efficiency of nitrogen elimination by up to 45% due to the build-up of high concentrations of nitrite. The concentration of sulphides, another source of pollution of the leachate, was also determined by triangle programmed coulometric titration. The average concentration of sulphides in the leachate was 221 mg/l (SD = 374 mg/l; n = 55). The sulphide concentrations decreased to concentrations below the detection limit of the coulometric titration (2 × 10^?6M) during nitrification.     

Fabrication of Bacteria Environment Cubes with Dry Lift-Off Fabrication Process for Enhanced Nitrification

We have developed a 3D dry lift-off process to localize multiple types of nitrifying bacteria in polyethylene glycol diacrylate (PEGDA) cubes for enhanced nitrification, a two-step biological process that converts ammonium to nitrite and then to nitrate. Ammonia-oxidizing bacteria (AOB) is responsible for converting ammonia into nitrite, and nitrite-oxidizing bacteria (NOB) is responsible for converting nitrite to nitrate. Successful nitrification is often challenging to accomplish, in part because AOB and NOB are slow growers and highly susceptible to many organic and inorganic chemicals in wastewater. Most importantly, the transportation of chemicals among scattered bacteria is extremely inefficient and can be problematic. For example, nitrite, produced from ammonia oxidation, is toxic to AOB and can lead to the failure of nitrification. To address these challenges, we closely localize AOB and NOB in PEGDA cubes as microenvironment modules to promote synergetic interactions. The AOB is first localized in the vicinity of the surface of the PEGDA cubes that enable AOB to efficiently uptake ammonia from a liquid medium and convert it into nitrite. The produced nitrite is then efficiently transported to the NOB localized at the center of the PEGDA particle and converted into non-toxic nitrate. Additionally, the nanoscale PEGDA fibrous structures offer a protective environment for these strains, defending them from sudden toxic chemical shocks and immobilize in cubes. This engineered microenvironment cube significantly enhances nitrification and improves the overall ammonia removal rate per single AOB cell. This approach—encapsulation of multiple strains at close range in cube in order to control their interactions—not only offers a new strategy for enhancing nitrification, but also can be adapted to improve the production of fermentation products and biofuel, because microbial processes require synergetic reactions among multiple species.     

与氮转化有关的土壤酶活性对抑制剂施用的响应

利用室内模拟培养试验,研究好气条件下施用尿素后土壤脲酶、脲酸还原酶、亚硝酸还原酶和羟胺还原酶活性对脲酶抑制剂氢醌（HQ）与硝化抑制剂包被碳化钙（ECC）和双氰胺（DCD）组合（HQ ECC、HQ DCD）的响应、结果表明,HQ DCD组合与其它抑制剂处理相比能更有效地降低土壤脲酶活性,增加硝酸还原酶、亚硝酸还原酶、羟胺还原酶活性,不同处理土壤脲酶、亚硝酸还原酶和羟胺还原酶活性与土壤NH4^ 、NO3^-、NH3挥发和N2O排放速率间存在不同形式的显著相关关系：土壤脲酶、亚硝酸还原酶和羟胺还原酶活性之间存在不同形式的显著正相关关系。     

Nitrification Rates in the Baltic Sea: Comparison of Three Isotope Techniques

Simultaneous measurements of nitrification in the Baltic Sea were made at 10- to 30-m intervals in the months of June and November by three isotope techniques: [¹⁵N]nitrate dilution, N-serve sensitive [¹⁴C]bicarbonate incorporation, and [¹⁵N]ammonium oxidation to nitrite and nitrate. Nitrification rates of 1 to 280 nmol liter⁻¹ day⁻¹ were recorded, and each method showed that the highest rates of nitrification occurred below the halocline. Even in the presence of ammonium, dark incubations of mixed layer (above ca. 50 m) waters never yielded nitrification rates exceeding 45 nmol liter⁻¹ day⁻¹. The rates measured by the ammonium oxidation method were two- to sevenfold greater than those obtained by ¹⁴C incorporation or ¹⁵N dilution. The merits of each technique are discussed, and it is suggested that the [¹⁵N]ammonium oxidation method should be used in conjunction with the [¹⁴C]bicarbonate incorporation method.