Interactions between Carbon and Nitrogen Mineralization and Soil Organic Matter Chemistry in Arctic Tundra Soils

We used long-term laboratory incubations and chemical fractionation to characterize the mineralization dynamics of organic soils from tussock, shrub, and wet meadow tundra communities, to determine the relationship between soil organic matter (SOM) decomposition and chemistry, and to quantify the relative proportions of carbon (C) and nitrogen (N) in tundra SOM that are biologically available for decomposition. In all soils but shrub, we found little decline in respiration rates over 1 year, although soils respired approximately a tenth to a third of total soil C. The lack of decline in respiration rates despite large C losses indicates that the quantity of organic matter available was not controlling respiration and thus suggests that something else was limiting microbial activity. To determine the nature of the respired C, we analyzed soil chemistry before and after the incubation using a peat fractionation scheme. Despite the large losses of soil C, SOM chemistry was relatively unchanged after the incubation. The decomposition dynamics we observed suggest that tundra SOM, which is largely plant detritus, fits within existing concepts of the litter decay continuum. The lack of changes in organic matter chemistry indicates that this material had already decomposed to the point where the breakdown of labile constituents was tied to lignin decomposition. N mineralization was correlated with C mineralization in our study, but shrub soil mineralized more and tussock soil less N than would have been predicted by this correlation. Our results suggest that a large proportion of tundra SOM is potentially mineralizable, despite the fact that decomposition was dependent on lignin breakdown, and that the historical accumulation of organic matter in tundra soils is the result of field conditions unfavorable to decomposition and not the result of fundamental chemical limitations to decomposition. Our study also suggests that the anticipated increases in shrub dominance may substantially alter the dynamics of SOM decomposition in the tundra. Received 31 January 2002; accepted 16 July 2002.     

Enumeration of Fe(II)-oxidizing and Fe(III)-reducing bacteria in the root zone of wetland plants: Implications for a rhizosphere iron cycle

Iron plaque occurs on the roots of most wetland and submersed aquatic plant species and is a large pool of oxidized Fe(III) in some environments. Because plaque formation in wetlands with circumneutral pH has been largely assumed to be an abiotic process, no systematic effort has been made to describe plaque-associated microbial communities or their role in plaque deposition. We hypothesized that Fe(II)-oxidizing bacteria (FeOB) and Fe(III)-reducing bacteria (FeRB) are abundant in the rhizosphere of wetland plants across a wide range of biogeochemical environments. In a survey of 13 wetland and aquatic habitats in the Mid-Atlantic region, FeOB were present in the rhizosphere of 92% of the plant specimens collected (n = 37), representing 25 plant species. In a subsequent study at six of these sites, bacterial abundances were determined in the rhizosphere and bulk soil using the most probable number technique. The soil had significantly more total bacteria than the roots on a dry mass basis (1.4 × 10⁹ cells/g soil vs. 8.6 × 10⁷ cells/g root; p < 0.05). The absolute abundance of aerobic, lithotrophic FeOB was higher in the soil than in the rhizosphere (3.7 × 10⁶/g soil vs. 5.9 × 10⁵/g root; p < 0.05), but there was no statistical difference between these habitats in terms of relative abundance (1% of the total cell number). In the rhizosphere, FeRB accounted for an average of 12% of all bacterial cells while in the soil they accounted for < 1% of the total bacteria. We concluded that FeOB are ubiquitous and abundant in wetland ecosystems, and that FeRB are dominant members of the rhizosphere microbial community. These observations provide a strong rationale for quantifying the contribution of FeOB to rhizosphere Fe(II) oxidation rates, and investigating the combined role of FeOB and FeRB in a rhizosphere iron cycle.     

水稻土中铁还原菌多样性

微生物介导的异化Fe(III) 还原是非硫厌氧环境中Fe(III) 还原生成Fe(II) 的主要途径,然而相关的铁还原菌还不是很清楚,特别是在水稻土中.本文采用富集培养的方法,以乙酸和氢气作为电子供体,水铁矿和针铁矿作为电子受体,通过末端限制性片段长度多态性（T-RFLP）技术和16S rRNA基因克隆测序相结合的分子生物学方法研究了水稻土中铁还原菌的多样性.结果表明：无论是以乙酸或氢气为电子供体,水铁矿或针铁矿为电子受体,地杆菌（Geobacter）和梭菌（Clostridiales）是富集到的主要微生物群落;乙酸为电子供体时,富集到的主要微生物群落还包括红环菌（Rhodocyclaceae）;因此,除地杆菌外,梭菌和红环菌很可能也是水稻土中重要的铁还原菌.     

水稻土中铁还原菌多样性

微生物介导的异化Fe(III) 还原是非硫厌氧环境中Fe(III) 还原生成Fe(II) 的主要途径,然而相关的铁还原菌还不是很清楚,特别是在水稻土中.本文采用富集培养的方法,以乙酸和氢气作为电子供体,水铁矿和针铁矿作为电子受体,通过末端限制性片段长度多态性（T-RFLP）技术和16S rRNA基因克隆测序相结合的分子生物学方法研究了水稻土中铁还原菌的多样性.结果表明：无论是以乙酸或氢气为电子供体,水铁矿或针铁矿为电子受体,地杆菌（Geobacter）和梭菌（Clostridiales）是富集到的主要微生物群落;乙酸为电子供体时,富集到的主要微生物群落还包括红环菌（Rhodocyclaceae）;因此,除地杆菌外,梭菌和红环菌很可能也是水稻土中重要的铁还原菌.     

海洋沉积物中铁还原细菌组成及异化铁还原与产氢性质分析

【背景】一些铁还原细菌具有异化铁还原与产氢的能力,该类细菌在环境污染修复的同时能够解决能源问题。【目的】从海洋沉积物中富集获得异化铁还原菌群,明确混合菌群组成、异化铁还原及产氢性质。获得海洋沉积物中异化铁还原混合菌群组成,分析菌群异化铁还原和产氢性质。【方法】利用高通量测序技术分析异化铁还原菌群的优势菌组成,在此基础上,分析异化铁还原混合菌群在不同电子供体培养条件下异化铁还原能力和产氢性质。【结果】高通量数据表明,在不溶性氢氧化铁为电子受体和葡萄糖为电子供体厌氧培养条件下,混合菌群的优势菌属主要是梭菌(Clostridium),属于发酵型异化铁还原细菌。混合菌群能够利用电子供体蔗糖、葡萄糖以及丙酮酸钠进行异化铁还原及发酵产氢。葡萄糖为电子供体时,菌群累积产生Fe(Ⅱ)浓度和产氢量最高,分别是59.34±6.73 mg/L和629.70±11.42 mL/L。【结论】异化铁还原混合菌群同时具有异化铁还原和产氢能力,拓宽了发酵型异化铁还原细菌的种质资源,探索异化铁还原细菌在生物能源方面的应用。     

Comparison of Humic Substance- and Fe(III)-Reducing Microbial Communities in Anoxic Aquifers

Humic substances can mediate electron transfer between microorganisms and Fe(III) minerals. Because it is unknown which microorganisms reduce humics in anoxic aquifers, we analyzed the diversity and physiological flexibility of Fe(III)-, humics-, and AQDS-reducers, which were present at up to 10⁶ cells g^?1. No significant differences in 16S rRNA gene based diversity were found between enrichment cultures reducing ferrihydrite, humics or AQDS. Even after repeated transfers many of the enrichments retained the ability to switch to other electron acceptors. This suggests that humics- and Fe(III)-reducing microorganisms in anoxic aquifers are rather versatile and able to reduce different extracellular electron acceptors.     

异化铁还原细菌LQ25还原重金属Cr (VI)的特性研究

[背景] 异化铁还原细菌能够在还原Fe （III）的同时将毒性较大的Cr （VI）还原成毒性较小的Cr （III）,解决铬污染的问题。[目的] 基于丁酸梭菌（Clostridium butyricum） LQ25异化铁还原过程制备生物磁铁矿,开展异化铁还原细菌还原Cr （VI）的特性研究。[方法] 构建以氢氧化铁为电子受体和葡萄糖为电子供体的异化铁培养体系。菌株LQ25培养结束时制备生物磁铁矿。设置不同初始Cr （VI）浓度（5、10、15、25和30 mg/L）,分别测定菌株LQ25对Cr （VI）还原效率以及生物磁铁矿对Cr （VI）的还原效率。[结果] 菌株LQ25在设置的Cr （VI）浓度范围内都能良好生长。当Cr （VI）浓度为15 mg/L时,在异化铁培养条件下,菌株LQ25对Cr （VI）的还原率为63.45%±5.13%,生物磁铁矿对Cr （VI）的还原率为87.73%±9.12%,相比菌株还原Cr （VI）的效率提高38%。pH变化能影响生物磁铁矿对Cr （VI）的还原率,当pH 2.0时,生物磁铁矿对Cr （VI）的还原率最高,几乎达到100%。电子显微镜观察发现生物磁铁矿表面有许多孔隙,X-射线衍射图谱显示生物磁铁矿中Fe （II）的存在形式是Fe （OH）₂。[结论] 基于异化铁还原细菌制备生物磁铁矿可用于还原Cr （VI）,这是一种有效去除Cr （VI）的途径。     

Naphthalene and Anthracene Mineralization Linked to Oxygen, Nitrate, Fe(III) and Sulphate Reduction in a Mixed Microbial Population

A microbial consortium from a mixture of garden soil and an enrichment of a coal-tar contaminated sediment mineralized naphthalene and anthracene when oxygen, nitrate, Fe(III) (soluble and insoluble) or sulphate were provided as terminal electron acceptors (TEAs). Rates of polyaromatic hydrocarbon disappearance and mineralization were similar in the presence of oxygen and nitrate, and slower with the other TEAs. A maximum mineralization of 37.5% naphthalene and 8.% anthracene occurred in 30 and 160 days respectively when oxygen was provided as the TEA. On the other hand, only 9.5% naphthalene and 3.2% anthracene were mineralized in 42 and 160 days respectively with FeOOH. Mineralization occurred only when a TEA was provided and ceased when the naphthalene concentration decreased to non-detectable levels (less than 0.008 moles/L), as measured by fluorescence spectroscopy. CH₄ was not detected in the headspace of any microcosm. These results showed that mineralization of polyaromatic hydrocarbons such as naphthalene and anthracene can be linked to wide range of TEAs demonstrating that intrinsic polyaromatic hydrocarbon bioremediation is possible if any of these TEAs were available.     

油藏铁还原微生物的研究进展

地下深部油藏通常为高温、高压以及高盐的极端环境,含有非常丰富的本源嗜热厌氧微生物,按代谢类群可分为发酵细菌、硫酸盐还原菌、产甲烷古菌和铁还原菌。从油田环境已经分离出90株铁还原微生物,如热袍菌目、热厌氧杆菌目、脱铁杆菌目、δ-变形菌纲脱硫单胞菌目、γ-变形菌纲希瓦氏菌属和广古菌门栖热球菌属等,这些菌株生长温度范围为4-85°C,生长盐度范围为0.1%-10.0%NaCl,还未见到文献报道油藏铁还原菌的耐压性研究。在油藏环境中存在微生物、矿物和流体(油/水)三者之间的相互作用,油藏中的粘土矿物能够作为微生物生命活动的载体,也能为微生物代谢作用提供电子受体。本文综述了油藏铁还原菌分离和表征的研究进展,简述了油藏铁还原菌的环境适用性,并展望了铁还原菌在提高原油采收率方面的应用前景。     

Microbial Response to Organic Matter Enrichment in the Oligotrophic Levantine Basin (Eastern Mediterranean)

The response of a deep-water benthic microbial community to organic matter (OM) enrichment was studied in the unexplored region of the SW Cretan margin (E. Mediterranean). A food pulse of 0.5 g C m^?2 was simulated by adding ¹³C-labelled diatoms to sediment cores retrieved from 1079 m depth. The diatom addition resulted in a significant increase in the sediment community oxygen consumption (SCOC). After 6 days, ～50 mg C m^?2 of the added material was processed by the microbial community. The major carbon sink was respiration, which accounted for ～96% of the total processed material. The carbon uptake rate (12 mg C m^?2 d^?1) was considerably lower than previously published values in the E. Mediterranean at similar depths. The microbial community in our study site is distinct, as revealed by the unusually high presence of branched phospholipid fatty acids (PLFA). Previous studies have revealed that the slope under investigation may act as a conduit of OM from the shallow shelf to the deep basins, resulting in the prevalence of relatively refractory OM at mid-slope depths. We postulate that sedimentary processes affect the amount of bioavailable sedimentary OM and consequently the structure and physiological state of bacterial community in our study site. The distinct microbial community composition at our station compared to more stable adjacent slopes could explain the limited response of the microbial community to the addition of labile OM. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental file.     

Mercury (II) Adsorption on Three Contrasting Chinese Soils Treated with Two Sources of Dissolved Organic Matter: II. Spectroscopic Characterization

To reveal the influencing mechanism of dissolved organic matter (DOM) on mercury (Hg II) adsorption by black, red, and fluvo-aquic soils in China, Fourier transform infrared (FTIR) spectroscopy, ¹³C nuclear magnetic resonance (NMR) spectroscopy, and three-dimensional excitation emission matrix (3DEEM) fluorescence spectroscopy were employed to characterize the DOM samples and DOM-Hg complexes. FTIR spectra showed that the complexation of Hg (II) mainly acted on the C=O, COO^?, and O-H groups of DOM from swine manure (DOMs) and wheat straw (DOMw). The NMR spectra indicated that the complex reaction of Hg (II) and DOM corresponded with the change in carboxyl C. The NMR results also showed that the dominant C components in DOM were aromatic C, O-alkyl C, alkyl C, and carboxyl C, and that DOMw imposed more influence on Hg (II) adsorption than DOMs, which was consistent with that of FTIR spectroscopy. The 3DEEM showed that DOM contained both aromatic protein-like and fulvic-like substances, and that the protein-like properties of DOMs and UV fulvic-like fluorescence substances of DOMw can better participate in the formation of Hg complexes. This result provides strong direct evidence to elucidate the DOM-Hg (II) binding mechanism, and further interprets the effect mechanism of exogenous DOM on Hg adsorption by soil.     

Competition of Fe(III) reduction and methanogenesis in an acidic fen

Peatlands are sources of relevant greenhouse gases such as CH4, but the temporal presence of Fe(III) may inhibit methanogenesis. Because excess of carbon during the vegetation period might allow concomitant electron-accepting processes, Fe(III) reduction and methanogenesis were studied during an annual season in an acidic fen. The upper peat layer displayed the highest Fe(II)- and CH4-forming activities. The rates of Fe(II) formation did not change during the year and methanogenesis started mostly when Fe(II) formation reached a plateau. Most of the Fe(III) pool seemed to be bioavailable, and addition of nitrilotriacetic acid stimulated only light Fe(II) formation, whereas EDTA and anthraquinone-2,6-disulfonate had no effect. In the presence of an inhibitor for methanogenesis (sodium 2-bromoethanesulfonate), Fe(II) formation was inhibited to 45%. Addition of Fe(III) during ongoing methanogenesis led only to a partial inhibition of CH4 formation. The proportion of acetoclastic methanogenesis varied between 42% and 90%, but no trend with time was observed. The number of acetate-, ethanol- or lactate-utilizing Fe(III) reducers approximated 10(5)-10(6) cells g (fresh wt peat)(-1). Fermentative glucose-utilizing Fe(III)-reducers were most abundant. Our results suggest that (1) methanogens used Fe(III) as an electron acceptor and (2) fermenting bacteria, which do not compete with methanogens for common electron donors, dominated the reduction of Fe(III) in this fen.     

Mercury (II) Adsorption on Three Contrasting Chinese Soils Treated with Two Sources of Dissolved Organic Matter: I. Langmuir and Freundlich Isotherm Evaluation

The behavior and fate of mercury (Hg) in soil is mainly controlled by adsorption and desorption processes with various adsorbents, particularly dissolved organic matter (DOM). This study was conducted to assess the effect of DOM from wheat straw (DOMw) and swine manure (DOMs) on Hg (II) adsorption of black, red, and fluvo-aquic soils in China. Results showed that the Hg (II) adsorption isotherms fitted well with Langmuir and Freundlich equations. The maximum Hg (II) potential adsorption capacity by the three soils followed this trend: black soil > red soil > fluvo-aquic soil. The amount of Hg (II) adsorbed on the soils significantly decreased when DOMw and DOMs were added to the soil samples. Furthermore, the extent by which DOMw affected the Hg (II) adsorption of the three soils was higher than the effect of equivalent amounts of DOMs. Therefore, DOM is important to determine the fate of Hg (II) and control Hg (II) pollution in the environment.     

Characteristics of Copper Sorption by Various Agricultural Soils in China and the Effect of Exogenic Dissolved Organic Matter on the Sorption

To explore the effect of exogenic dissolved organic matter (DOM) on Cu(II) sorption in agricultural soils, 26 agricultural soils were collected across China. Exogenic dissolved organic matter, extracting from wheat straw (DOM_W) and swine manure (DOM_S), respectively, were added to the soils to conduct a series of batch sorption and characterization experiments. The solid-liquid partition coefficient (K_d) ranged from 0.02 to 76.46 L g^?1, suggesting different Cu(II) sorption on various soils. PCA analysis indicated that pH, free Fe/Al oxides, carbon, and total Cu content had a significant positive relationship with the Cu(II) sorption, respectively. And the contribution rate of pH was the highest (38.15%). Moreover, DOM markedly inhibited the Cu(II) sorption in alkaline soils while promoted the Cu(II) sorption in acidic soils, which were interacted by the soil properties and DOM characteristics. The effect of DOM_S on Cu(II) sorption were more obvious than DOM_W, which were further confirmed by Fourier transform infrared (FTIR) spectroscopy. FTIR also showed Cu(II) was primarily adsorbed on the specific functional groups, such as CO, OH, and CO, providing direct evidences for the binding of Cu(II) with DOM. This study can guide the rational use of organic fertilizers, and also provide baseline knowledge for the prevention and control of soil pollution.     

A Novel Electrochemically Active and Fe(III)-reducing Bacterium Phylogenetically Related to Clostridium butyricum Isolated from a Microbial Fuel Cell

An obligatory anaerobic bacterium was isolated from a mediator-less microbial fuel cell using starch processing wastewater as the fuel and designated as EG3. The isolate was Gram-positive, motile and rod (2.8–3.0 μm long, 0.5–0.6 μm wide). The partial 16S rRNA gene sequence and analysis of the cellular fatty acids profile suggested that EG3 clusters with Clostridium sub-phylum and exhibited the highest similarity (98%) with Clostridium butyricum. The temperature and pH optimum for growth were 37°C and 7.0, respectively. The major products of glucose and glucose/Fe(O)OH metabolism were lactate, formate, butyrate, acetate, CO₂and H₂. Growth was faster at the initial phase and the cell yield was higher when the medium was supplemented with Fe(O)OH than without Fe(O)OH. These results suggest that Fe(III) ion is utilised as an electron sink. Cyclic voltammetry showed that Clostridium butyricum EG3 cells were electrochemically active. It is a novel characteristic of strict anaerobic Gram-positive bacteria.     

Assessment of Nitrate Removal Coupled with Fe (II) Oxidation and Analysis of Microbial Communities in a Moving-Bed Biofilm Reactor

A moving-bed biofilm reactor (MBBR) was used with an immobilized Pseudomonas sp. SZF15 strain in a Yu long filter (a novel bioactive carrier), which has the ability to remove nitrate and Fe (II) simultaneously. Optimum operating conditions were achieved with a nitrate removal ratio of 95.62% and an Fe (II) oxidation ratio of 88.09%. Meanwhile, high-throughput sequencing results confirmed that the immobilized Pseudomonas sp. SZF15 was not lost during the operation. This study lays the foundation for practical application of groundwater treatment.     

A novel electrochemically active and Fe(III)-reducing bacterium phylogenetically related to Aeromonas hydrophila,isolated from a microbial fuel cell

A facultative anaerobic bacterium was isolated from a mediator-less microbial fuel cell fed with artificial wastewater containing acetate and designated as PA3. The isolate was identified as a strain of Aeromonas hydrophila based on its biochemical, physiological and morphological characteristics as well as 16S rDNA sequence analysis and DNA-DNA hybridization. PA3 used glucose, glycerol, pyruvate and hydrogen to reduce Fe(III), nitrate and sulfate. Cyclic voltammetry showed that PA3 was electrochemically active and was the culture collection strain A. hydrophila KCTC 2358. Electricity was generated from a fuel cell-type reactor, the anode compartment of which was inoculated with cell suspensions of the isolate or A. hydrophila KCTC 2358. The electrochemical activities are novel characteristics of A. hydrophila.