添加氧化铁对水稻土中H2、CO2和CH4形成的影响

水稻土是甲烷产生的重要源地.厌氧条件下甲烷的形成与有机质厌氧降解产生的乙酸、H₂和CO₂有关.氧化铁作为电子受体可有效地竞争有机质向甲烷的转化,其抑制作用机理可能与乙酸、H₂和CO₂的有效消耗有关.通过向水稻土泥浆中添加无定形氧化铁和纤铁矿,分别测定了25℃厌氧恒温培养105d过程中的H₂、CO₂和CH₄的浓度变化.结果表明,添加无定形氧化铁及纤铁矿可导致H₂浓度显著降低;无定形氧化铁对H₂消耗的影响明显大于纤铁矿;添加不同氧化铁对CO₂浓度的影响与H₂浓度的变化有相同的趋势;添加氧化铁能显著抑制水稻土中甲烷形成,并导致有机碳的转移发生变化,使得CH₄-C显著降低,气相中CO₂-C量减少,而由土壤泥浆固定的CO₃^2--C量显著增加.     

外源表油菜素内酯对NaHCO3胁迫下黄瓜幼苗生长及氧化还原平衡的影响

以‘津研四号’黄瓜为试材,以30 mmol·L^-1 NaHCO₃模拟盐碱环境,采用水培法研究了0.2 μmol·L^-1外源2,4表油菜素内酯(2,4-epibrassinolide,EBR)对盐碱胁迫下黄瓜幼苗生长和活性氧代谢的影响.结果表明: NaHCO₃胁迫显著诱导了叶片及根系中O₂^-·的产生和H₂O₂的积累,导致丙二醛含量和电解质渗透率提高.NaHCO₃胁迫下,超氧化物歧化酶、过氧化物酶、过氧化氢酶、抗坏血酸过氧化物酶、脱氢抗坏血酸还原酶、单脱氢抗坏血酸还原酶、谷胱甘肽还原酶活性及还原型抗坏血酸、还原型谷胱甘肽含量随胁迫时间延长呈现先升后降的趋势.外源EBR显著提高了NaHCO₃胁迫下黄瓜叶片和根系中抗氧化酶活性、抗氧化物质的含量以及AsA/DHA(双脱氢抗坏血酸)和GSH/GSSG(氧化型谷胱甘肽)比值,维持了植株内的氧化还原平衡,降低了活性氧积累水平,缓解了膜脂过氧化,从而提高了黄瓜幼苗的盐碱耐受性.     

施氮和大气CO2浓度升高对小麦旗叶光合电子传递和分配的影响

采用开顶式气室盆栽培养小麦,设计2个大气CO₂浓度（正常：400 μmol·mol^-1;高：760 μmol·mol^-1）、2个氮素水平（0和200 mg·kg^-1土）的组合处理,通过测定小麦抽穗期旗叶氮素和叶绿素浓度、光合速率（P_n）-胞间CO₂浓度（C_i）响应曲线及荧光动力学参数,来测算小麦叶片光合电子传递速率等,研究了高大气CO₂浓度下施氮对小麦旗叶光合能量分配的影响.结果表明：与正常大气CO₂浓度相比,高大气CO₂浓度下小麦叶片氮浓度和叶绿素浓度降低,高氮处理的小麦叶片叶绿素a/b升高.施氮后小麦叶片PSⅡ最大光化学效率（F_v/F_m）、PSⅡ反应中心最大量子产额（F_v′/F_m′）、PSⅡ反应中心的开放比例（q_p）和PSⅡ反应中心实际光化学效率（Φ_PSⅡ）在大气CO₂浓度升高后无明显变化,虽然叶片非光化学猝灭系数（NPQ）显著降低,但PSⅡ总电子传递速率（J_F）无明显增加;不施氮处理的F_v′/F_m′、Φ_PSⅡ和NPQ在高大气CO₂浓度下显著降低,尽管F_v/F_m和q_P无明显变化,J_F仍显著下降.施氮后小麦叶片J_F增加,参与光化学反应的非环式电子流传递速率(J_C)明显升高.大气CO₂浓度升高使参与光呼吸的非环式电子流传递速率(J₀)、Rubisco氧化速率（V₀）、光合电子的光呼吸/光化学传递速率比（J₀/J_C）和Rubisco氧化/羧化比（V₀/V_C）降低,但使J_C和Rubisco羧化速率（V_C）增加.因此,高大气CO₂浓度下小麦叶片氮浓度和叶绿素浓度降低,而增施氮素使通过PSⅡ反应中心的电子流速率显著增加,促进了光合电子流向光化学方向的传递,使更多的电子进入Rubisco羧化过程,P_n显著升高.     

2,4-二氯苯酚在土壤与河流底泥中降解动力学

以南京化学工业园内四柳河沿岸土壤与河流底泥为研究对象,通过土壤灭菌、温度与污染物初始浓度调控,研究了2,4-二氯苯酚在土壤与河流底泥中降解动力学及其影响因子。结果表明:微生物对2,4-二氯苯酚降解起主导作用,在45d内,非灭菌土壤和河流底泥的降解率分别是灭菌条件下的1.5～3倍、1.4～2.8倍,土壤和河流底泥中的2,4-二氯苯酚微生物降解量分别为0.128～0.599和0.113～0.718mg·kg-1,非灭菌处理半衰期时间短于灭菌处理;(10±1)℃～(30±1)℃范围内,随着温度的增高,2,4-二氯苯酚降解加快,在(30±1)℃土壤与河流底泥中残留量最小,分别为0.305和0.203mg·kg-1,半衰期也最短;土壤与河流底泥中的2,4-二氯苯酚均在其浓度为0.5mg·kg-1时降解最快,随着初始浓度的增加,2,4-二氯苯酚降解速度呈现递减趋势,半衰期增长。     

干湿交替灌溉下不同稗草种对水稻产量及生理特性的影响

以两优培九(籼稻)和南粳9108(粳稻)为材料,从移栽至成熟期分别与无芒稗(T₁)、稗(T₂)、西来稗(T₃)和光头稗(T₄)共生,以无稗草水稻处理为对照,研究干湿交替灌溉条件下不同稗草种对水稻产量和生理特性的影响.结果表明： 与对照相比,T₁、T₂、T₃和T₄处理下两优培九分别减产13.8%、10.6%、23.8%和0.5%,南粳9108分别减产45.5%、36.9%、60.7%和15.1%.T₁、T₂和T₃处理显著降低了水稻产量,T₄处理对两优培九产量无显著影响,但显著降低了南粳9108的产量.T₁、T₂、T₃和T₄处理增加了水稻灌浆期叶片丙二醛含量,降低了叶片中过氧化氢酶、过氧化物酶和超氧化物歧化酶的活性,降低了成熟期干物质积累量、灌浆期根系氧化力以及根系中吲哚-3-乙酸和玉米素+玉米素核苷的含量.4种处理对水稻各生理指标的影响程度为T₃>T₁>T₂>T₄.稻-稗共生时水稻灌浆期叶片抗氧化系统酶活性、根系氧化力、根系中吲哚-3-乙酸和玉米素+玉米素核苷含量及成熟期干物质积累量的降低以及灌浆期叶片丙二醛含量的增加是水稻减产的重要原因.     

厌氧微生物菌群XH-1对2,4,6-三氯苯酚的降解特性

有机污染物2,4,6-三氯苯酚(2,4,6-TCP)普遍存在于地下水和河流底泥等厌氧环境中。为了探究厌氧微生物菌群XH-1对2,4,6-TCP的降解能力,本研究以2,4,6-TCP为底物,接种XH-1建立微宇宙培养体系,并以中间产物4-氯苯酚(4-CP)和苯酚为底物分别进行分段富集培养,利用高效液相色谱分析底物的降解转化,同时基于16S rRNA基因高通量测序分析微生物群落结构变化。结果表明: 2,4,6-TCP(122 μmol·L^-1)以0.15 μmol·d^-1的速率在80 d内被完全降解转化,降解中间产物分别为2,4-二氯苯酚(2,4-DCP)、4-氯苯酚和苯酚,所有中间产物最终在325 d被完全降解。高通量测序结果表明,脱卤杆菌和脱卤球菌可能驱动2,4,6-TCP还原脱氯,其中,脱卤球菌可能在4-CP的脱氯转化中发挥重要作用,并与丁酸互营菌和产甲烷菌联合作用彻底降解2,4,6-TCP。     

豌豆根系中分泌物质的分离鉴定及其化感效应的研究

本文实验采用GC-MS分析法对豌豆组培苗、土培苗重茬两代的根系分泌物进行鉴定。实验结果表明,能被二氯甲烷提取的豌豆根系分泌物有醇类、脂类、醛类、苯类、烃类等。用不同浓度的豌豆化感物质2,4-二叔丁基苯酚(2,4-DB)和2,6-二叔丁基对甲酚(2,6-DM)处理豌豆、绿豆、小麦和玉米4种作物种子,进行萌发和幼苗生长的化感效应研究。结果表明,0~2 mmol·L~(-1) 2,4-DB和2,6-DM处理对豌豆和绿豆种子萌发呈促进作用,而3~5 mmol·L~(-1) 2,4-DB和2,6-DM处理则呈抑制的作用。随浓度的增大,2种化感物质对小麦和玉米种子萌发的抑制作用逐渐增强。对于豆科作物豌豆和绿豆,2,4-DB对绿豆萌发时根系的抑制作用较强;而对于禾本科作物玉米和小麦,则2,4-DB对小麦萌发时根系的抑制作用最强。     

稗属杂草对水稻生长发育和产量的影响

以新两优6号(籼稻)和南粳46(粳稻)为材料,自水稻移栽至成熟分别与无芒稗(T₁)、稗(T₂)、西来稗(T₃)和光头稗(T₄)共生,稗草密度为6株·m^-2,以无稗草水稻处理为对照,研究不同稗草对水稻生长发育和产量的影响.结果表明：与对照相比,不同稗草对水稻的干扰表现不同,T₁、T₂、T₃处理使籼稻产量分别下降19.2%、10.8%、21.9%,使粳稻产量分别下降39.7%、25.3%、47.3%,但T₄处理对2个水稻品种的产量均无显著影响.水稻和稗草共生过程中,T₁、T₂和T₃处理显著降低了水稻成熟期的干物质积累量及灌浆期的剑叶光合速率、根系氧化力和籽粒ATP酶活性,降低幅度为T₃>T₁>T₂,T₄处理与对照差异不显著;各处理对水稻最终分蘖数和株高均无显著影响.表明4种稗草对水稻生长的影响由强到弱表现为：T₃>T₁>T₂>T₄,稻 稗共生时水稻剑叶光合速率、根系氧化力和籽粒ATP酶活性降低是导致水稻生产力下降的重要原因.     

土壤水势对水曲柳幼苗水分生态的影响

采用根区渗灌控水技术,将土壤水势长期控制在0～-20kPa(W₁)、-20～-40kPa(W₂)、-40～-60kPa(W₃)、-60～-80kPa(W₄)、-80～-160kPa(W₅)范围内,系统地研究了不同土壤水势条件下水曲柳幼苗的蒸腾过程、吸水过程、根叶水势日动态过程及SPAC体系的水流阻力.结果表明,在亚饱和土壤水分状态下(W₁),细根水势最高,水分由土壤进入细根的阻力最小,根系吸水速率最高,从而支持了日间强烈的蒸腾作用.在田间持水量土壤水分状态下(W₂),细根吸水阻力成倍增加,吸水速率和蒸腾速率显著下降,但尚未改变蒸腾作用日动态过程的单峰模式.当土壤水分在田间持水量状态以下(W₃～W₅)时,随着土壤水势递降,细根吸水阻力急剧增加至几倍乃至几十倍,根系吸水速率过低,吸水与蒸腾矛盾加剧,叶水势降至很低,气孔关闭,蒸腾作用受到严重抑制,呈现明显的午休低谷.在实验范围内(0～-160kPa),土壤水分对水曲柳幼苗是非等效的,当土壤水分在田间持水量状态以下(<-40kPa)时,水曲柳全光苗发生显著的水分胁迫.     

万峰湖水库溶解性无机碳来源及时空变异特征

溶解性无机碳(DIC)的通量和形式在水生态系统的生物地球化学循环中起关键作用,是碳收支的重要组成部分。通过分析万峰湖水库库区水体理化参数、DIC和稳定碳同位素(δ¹³C_DIC)特征,揭示了DIC的行为和来源。结果表明: 1)在表水层,整个库区pH变化较保守,均呈弱碱性。硝酸盐氮(NO₃^--N)有最大变异系数,具有高度的时空变异性。由于稀释效应的存在,电导率(EC)、二氧化碳分压(pCO₂)和DIC的最低值均出现在夏季高径流量阶段。在水柱面上,夏季氧化还原电位(Eh)和NO₃^--N随水深增加无显著变化,其余指标均变化明显,且在温跃层变异程度最大。两季节的水温(T)、pH和Eh均随水深增加而降低,pCO₂则与之相反。EC、总碱度(TA)和DIC在夏季随水深增加而降低,冬季变化梯度较小。两季节的DIC与pH、Eh呈负相关,与EC、pCO₂呈正相关。2)夏季DIC为2.66～4.9 mmol·L^-1,而冬季为3.38～4.52 mmol·L^-1。水体热分层期间,DIC和δ¹³C_DIC在温跃层的变化梯度最大,DIC与δ¹³C_DIC在夏季表水层呈正相关。两个季节水柱面上及冬季表水层的DIC和δ¹³C_DIC均呈负相关,但冬季DIC和δ¹³C_DIC值随水深变化趋势不明显。3)夏季δ¹³C_DIC较高,为-7.71‰～-1.38‰,表明碳酸盐矿物的溶解占优势。冬季δ¹³C_DIC为-16.93‰～-9.44‰,显著低于夏季且范围更宽,生物源CO₂的输入和有机质矿化是主要来源。δ¹³C_DIC在不同季节和水深均差异显著,一方面是碳的来源不同;另一方面归因于碳来源的相对贡献比例的变化。     

Behavior of Cu and Zn under combined pollution of 2,4-dichlorophenol in the planted soil

Behavior of heavy metals under combined pollution of 2,4-dichlorophenol (2,4-DCP) was investigated using metal contaminated soil which was sampled from the heavily industrialized areas, Fuyang county, Zhejiang Province, P.R. China and pretreated with 100 μg g^?1 2,4-DCP for 1 month. Metal complexes were the predominant species for Cu and Zn in the soil solution. The treatment of 2,4-DCP had limited effect on the dissolution of Cu and Zn in the soil without plant root growth. But the metal species might be changed due to the addition of organic pollutant. Planting with rye grass for 1 month, greatly increased both water soluble Cu and Zn. The increase of water soluble Cu and Zn in the presence of 2,4-DCP was much more than that in the absence of 2,4-DCP, which suggested more attention should be paid to the behavior of heavy metals under combined pollution of organic pollutants in the planted soil. The results also indicated that in comparison to Cu, soil planted with ryegrass was more effective in activating Zn from soils, which was consistent with its relative weak chemisorptions on clays, oxides and humus of soils.     

Simultaneous and Repetitious Removal of 2,4-Dichlorophenol and Copper from Soils Using an Aqueous Solution of Ethyl-Lactate-Amended EDDS

Heavy metals and the transformation products of herbicides, such as 2,4-dichlorophenol (2,4-DCP), are toxic soil pollutants. We assessed the ability of an aqueous solution of the “green solvent” ethyl lactate alone and combined with [S,S]-ethylenediaminedisuccinic acid (EDDS) to remove 2,4-DCP and copper simultaneously from soils. Ethyl lactate extracted 2,4-DCP from contaminated soil comparable to Triton X-100. Ethyl lactate/EDDS extracted more 2,4-DCP and Cu from contaminated soils than ethyl lactate alone. The enhanced extraction of Cu increased slightly with an increase in the EDDS/Cu molar ratio; the maximum Cu extraction efficiency was about 32.3% at an EDDS/Cu ratio of 5. An increase in the ionic strength (NaCl) of the ethyl lactate/EDDS solution decreased the amount of 2,4-DCP extracted by maximally 12% but increased the amount of Cu extracted by >500%. We tested the recycling of the ethyl lactate/EDDS solution with the cation-exchange resin 001×7 and the hyper-cross-linked polymer resin NDA-150. Fresh ethyl lactate/EDDS solution and two sequentially recycled solutions removed 31.4, 28.3, and 26.7% of the Cu in Cu-contaminated soil and 77.7, 62.9, and 56.8% of the 2,4-DCP in 2,4-DCP-contaminated soils, respectively. The ethyl lactate/EDDS solution removed 31.8% of the Cu and 73.0% of the 2,4-DCP in Cu- and 2,4-DCP-contaminated soils, and the solution remained effective even after two recyclings. The aqueous solution of ethyl lactate/EDDS can be used to effectively remove Cu and 2,4-DCP from complex contaminated soils and can be reactivated.     

Geomicrobiology of manganese(II) oxidation

Mn(II)-oxidizing microbes have an integral role in the biogeochemical cycling of manganese, iron, nitrogen, carbon, sulfur, and several nutrients and trace metals. There is great interest in mechanistically understanding these cycles and defining the importance of Mn(II)-oxidizing bacteria in modern and ancient geochemical environments. Linking Mn(II) oxidation to cellular function, although still enigmatic, continues to drive efforts to characterize manganese biomineralization. Recently, complexed-Mn(III) has been shown to be a transient intermediate in Mn(II) oxidation to Mn(IV), suggesting that the reaction might involve a unique multicopper oxidase system capable of a two-electron oxidation of the substrate. In biogenic and abiotic synthesis experiments, the application of synchrotron-based X-ray scattering and spectroscopic techniques has significantly increased our understanding of the oxidation state and relatively amorphous structure (i.e. delta-MnO(2)-like) of biogenic oxides, providing a new blueprint for the structural signature of biogenic Mn oxides.     

Degradation of chlorophenols catalyzed by laccase

The degradations of 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 2-chlorophenol (2-CP) catalyzed by laccase were carried out. The optimal condition regarding degradation efficiency was also discussed, which included reaction time, pH value, temperature, concentration series of chlorophenols and laccase. Results showed that the capability of laccase was the best, while to oxidize 2,4-DCP among the above-mentioned chlorophenols. Within 10 h, the removal efficiency of 2,4-DCP, 2-CP and 4-CP could reach 94%, 75% and 69%, respectively. The optimal pH for laccase to degrade chlorophenols was around 5.5. The increase of laccase concentration or temperature might result in the degradation promotion. The trends of degradation percentage were various among these three chlorophenols with the concentration increase of chlorophenols. Degradation of 2,4-DCP is a first-order reaction and the reaction activation energy is about 44.8 kJ mol⁻¹. When laccase was immobilized on chitosan, crosslinked with glutaraldehyde, the activity of immobilized laccase was lower than that of free laccase, but the stability improved significantly. The removal efficiency of immobilized laccase to 2,4-DCP still remained over 65% after six cycles of operation.     

Cadmium removal and 2,4-dichlorophenol degradation by immobilized Phanerochaete chrysosporium loaded with nitrogen-doped TiO2 nanoparticles

Phanerochaete chrysosporium has been identified as an effective bioremediation agent for its biosorption and degradation ability. However, the applications of P. chrysosporium are limited owing to its long degradation time and low resistance to pollutants. In this research, nitrogen-doped TiO₂ nanoparticles were loaded on P. chrysosporium to improve the remediation capacity for pollutants. The removal efficiencies were maintained at a high level: 84.2 % for Cd(II) and 78.9 % for 2,4-dichlorophenol (2,4-DCP) in the wide pH range of 4.0 to 7.0 in 60 h. The removal capacity of immobilized P. chrysosporium loaded with nitrogen-doped TiO₂ nanoparticles (PTNs) was strongly affected by the initial Cd(II) and 2,4-DCP concentrations. The hyphae of PTNs became tight, and a large amount of crystals adhered to them after the reaction. Fourier transform infrared spectroscopy showed that carboxyl, amino, and hydroxyl groups on the surface of PTNs were responsible for the biosorption. In the degradation process, 2,4-DCP was broken down into o-chlorotoluene and 4-hexene-1-ol. These results showed that PTNs is promising for simultaneous removal of Cd(II) and 2,4-DCP from wastewater.     

Metal ion substrate inhibition of ferrochelatase

Ferrochelatase catalyzes the insertion of ferrous iron into protoporphyrin IX to form heme. Robust kinetic analyses of the reaction mechanism are complicated by the instability of ferrous iron in aqueous solution, particularly at alkaline pH values. At pH 7.00 the half-life for spontaneous oxidation of ferrous ion is approximately 2 min in the absence of metal complexing additives, which is sufficient for direct comparisons of alternative metal ion substrates with iron. These analyses reveal that purified recombinant ferrochelatase from both murine and yeast sources inserts not only ferrous iron but also divalent cobalt, zinc, nickel, and copper into protoporphyrin IX to form the corresponding metalloporphyrins but with considerable mechanistic variability. Ferrous iron is the preferred metal ion substrate in terms of apparent k(cat) and is also the only metal ion substrate not subject to severe substrate inhibition. Substrate inhibition occurs in the order Cu(2+) > Zn(2+) > Co(2+) > Ni(2+) and can be alleviated by the addition of metal complexing agents such as beta-mercaptoethanol or imidazole to the reaction buffer. These data indicate the presence of two catalytically significant metal ion binding sites that may coordinately regulate a selective processivity for the various potential metal ion substrates.     

Production of extracellular polymeric substances from Rhodopseudomonas acidophila in the presence of toxic substances

A hydrogen-producing photosynthetic bacteria strain, Rhodopseudomonas acidophila, was used to investigate the production of extracellular polymeric substances (EPS) in the presence of toxic substances and the effect of toxicants on bacterial surface characteristics. Addition of the toxic substances including Cu(II), Cr(VI), Cd(II) and 2,4-dichlorophenol (2,4-DCP) stimulated the production of EPS but reduced the cell dry weight. At concentrations of 30 mg l⁻¹ Cu(II), 40 mg l⁻¹ Cr(VI), 5 mg l⁻¹ Cd(II) and 100 mg l⁻¹ 2,4-DCP, the EPS content increased by 5.5, 2.5, 4.0 and 1.4 times, respectively, than the control. These toxic substances also greatly influenced the proteins/carbohydrates ratio of EPS. The ratios in the presence of toxic substances were always higher than that of control. Furthermore, under toxic conditions, the increase in the protein content far exceeded than that of others in EPS, suggesting that extracellular proteins could protect cells against toxic substances. The toxic substances significantly changed the surface characteristics and flocculation ability of R. acidophila, such as surface energy, relative hydrophobicity and free energy of adhesion.     

Kinetic and isothermal studies on liquid-phase adsorption of 2,4-dichlorophenol by palm pith carbon

Adsorption studies were conducted to study the removal of 2,4-dichlorophenol (2,4-DCP) from aqueous solution on palm pith carbon under varying experimental conditions such as agitation time, adsorbent dose, pH and temperature. Higher 2,4-DCP was removed with decrease in the initial concentration of 2,4-DCP and increase in amount of adsorbent used. Kinetic study showed that the adsorption of 2,4-DCP on palm pith carbon was a gradual process. Adsorption capacities were 19.16 mg/g for the particle size of 250-500 microm. The equilibrium time was 60 and 80 min for 10 and 20 mg/L and 100 min for both 30 and 40 mg/L phenol concentrations, respectively. Acidic pH was favourable for the adsorption of 2,4-DCP. Studies on pH effect and desorption showed that chemisorption seemed to play a major role in the adsorption process. Thermodynamic study showed that adsorption of 2,4-DCP on palm pith carbon was more favoured. The change in entropy (DeltaS0) and heat of adsorption (DeltaH0) of palm pith carbon was estimated as 30.72 J/mol/k and 7.16 kJ/mol, respectively. The high positive value of change in Gibbs free energy indicated the feasible and spontaneous adsorption of 2,4-DCP on palm pith carbon. The results indicated that palm pith carbon was an attractive candidate for removing phenols from wastewater.     

Biodegradation kinetics of 2,4-dichlorophenol by acclimated mixed cultures

The biodegradation kinetics of 2,4-dichlorophenol (2,4-DCP) by culture (Culture M) acclimated to mixture of 4-chlorophenol (4-CP) and 2,4-DCP and the culture (Culture 4) acclimated to 4-CP only were investigated in aerobic batch reactors. Also, pure strains isolated from mixed cultures were searched for their ability towards the biodegradation of 2,4-DCP. Culture 4 was able to completely degrade 2,4-DCP up to 80 mg/L within 30 h and removal efficiency dropped to 21% upon increasing initial concentration to 108.8 mg/L. When the Culture M was used, complete degradation of 2,4-DCP in the range of 12.5-104.4 mg/L was attained. A linear relationship between time required for complete degradation and initial 2,4-DCP concentrations was observed for both mixed cultures. It was observed that the Haldane equation can be used to predict specific degradation rate (SDR) (R(2)>0.99) as a function of initial 2,4-DCP concentrations and it adequately describes 2,4-DCP concentration profiles. Both of the mixed cultures settled well, which is important to maintain good removal efficiency for longer periods of time for real full-scale applications. Although the pure strains isolated from mixed cultures were found to have higher SDR of 2,4-DCP compared to mixed cultures, they did not settle well under quiescent conditions.     

Dominance of ‘Gallionella capsiferriformans’ and heavy metal association with Gallionella‐like stalks in metal‐rich pH 6 mine water discharge

Heavy metal‐contaminated, pH 6 mine water discharge created new streams and iron‐rich terraces at a creek bank in a former uranium‐mining area near Ronneburg, Germany. The transition from microoxic groundwater with ~5 mm Fe(II) to oxic surface water may provide a suitable habitat for microaerobic iron‐oxidizing bacteria (FeOB). In this study, we investigated the potential contribution of these FeOB to iron oxidation and metal retention in this high‐metal environment. We (i) identified and quantified FeOB in water and sediment at the outflow, terraces, and creek, (ii) studied the composition of biogenic iron oxides (Gallionella‐like twisted stalks) with scanning and transmission electron microscopy (SEM, TEM) as well as confocal laser scanning microscopy (CLSM), and (iii) examined the metal distribution in sediments. Using quantitative PCR, a very high abundance of FeOB was demonstrated at all sites over a 6‐month study period. Gallionella spp. clearly dominated the communities, accounting for up to 88% of Bacteria, with a minor contribution of other FeOB such as Sideroxydans spp. and ‘Ferrovum myxofaciens’. Classical 16S rRNA gene cloning showed that 96% of the Gallionella‐related sequences had ≥97% identity to the putatively metal‐tolerant ‘Gallionella capsiferriformans ES‐2’, in addition to known stalk formers such as Gallionella ferruginea and Gallionellaceae strain R‐1. Twisted stalks from glass slides incubated in water and sediment were composed of the Fe(III) oxyhydroxide ferrihydrite, as well as polysaccharides. SEM and scanning TEM‐energy‐dispersive X‐ray spectroscopy revealed that stalk material contained Cu and Sn, demonstrating the association of heavy metals with biogenic iron oxides and the potential for metal retention by these stalks. Sequential extraction of sediments suggested that Cu (52–61% of total sediment Cu) and other heavy metals were primarily bound to the iron oxide fractions. These results show the importance of ‘G. capsiferriformans’ and biogenic iron oxides in slightly acidic but highly metal‐contaminated freshwater environments.