低剂量混合稀土积累对黄褐土微生物主要类群的生态效应

采用田间小区试验和室内低剂量模拟叠加试验相结合的方法,研究低剂量混合稀土在黄褐土中积累对土壤微生物主要类群的生态效应．结果表明,低剂量稀土的持续积累对土壤细菌、放线菌产生刺激、抑制、再刺激的交替作用;对真菌也产生类似的作用,但抑制作用不显著,而刺激作用持续、明显．混合稀土对3类土壤微生物数量抑制程度顺序为：细菌>放线菌>霉菌．稀土积累至150mg·kg^-1时,土壤各类微生物的种群结构均发生显著的改变,耐稀土微生物数量大幅度增加,细菌中的G^-细菌、链霉菌的白孢类群、真菌中青霉分别成为优势种群．对低浓度稀土积累的田问土壤微生物学参数模拟计算结果表明,稀土对土壤细菌、放线菌和真菌的EC50(半抑制浓度)值分别为24．1、41．6～73．8和55．3～150．1mg·kg^-1,30mg·kg^-1值可以初步确定为稀土在黄褐土中积累的安全临界值．     

黑龙江不同玉米秸秆还田方式下土壤动物群落结构及其对秸秆降解的影响

以黑龙江省海伦市典型黑土耕地为试验样区,研究黑土区不同秸秆还田方式下土壤动物群落结构特征及其在秸秆降解中的作用。实验选取6目、30目、260目降解袋,设置5个处理:17kg玉米秸秆+2kg水还田+含微生物100%浓度催腐剂(样方A)、8.5kg玉米秸秆+1kg水还田+含微生物50%浓度催腐剂(样方B)、原始样方(样方C)、8.5kg玉米秸秆+1kg水还田(样方D)、17kg玉米秸秆+2kg水还田(样方E),并于2009—2011每年9月份测定不同样方的玉米秸秆降解率和微生物数量。结果表明:所有样方累积秸秆降解率都达55%以上,秸秆降解率从高到低排序依次为:样方A>样方B>样方C>样方D>样方E;对秸秆降解起主要作用的动物类群为中小型土壤动物中的甲螨亚目、中气门亚目和节跳虫科,约占土壤动物个体数的86.70%;不同处理样方中,土壤动物群落结构相似;相同处理样方中,不同规格的降解袋中土壤动物个数与类群差异显著(P<0.001);不同孔径降解袋中土壤动物的个数、类群数、多样性基本都与秸秆降解率呈正相关,进一步表明土壤动物对秸秆降解具有促进作用。     

电动修复过程中电压对土壤中芘降解及微生物群落的影响

电动-微生物修复是一种新型的有机污染土壤修复技术。本文研究了修复过程中电压对土壤中芘降解及微生物群落的影响。结果表明,在不同电压梯度处理下,土壤中的芘降解与土壤微生物群落组成在阳极区和阴极区呈现不同的分布特征。阳极区芘降解与电压呈显著的正相关(r=0.55,P0.01),在电压为2.0 V·cm-1时,阳极附近芘的降解率达到最高值(87.5%);阴极区芘的降解随着电压增大先升高后降低,电压为1.2 V·cm-1时阴极附近芘的降解率达到最高值(87.8%)。阳极区微生物活性和多样性与电压呈负相关;而阴极区微生物活性和多样性与芘降解的变化趋势相同。从芘的降解率和微生物群落结构来看,1.2 V·cm-1为本实验最合适的电压,该电压既保证了一定的电动氧化作用又促进了微生物发挥其最大的代谢降解能力。本研究为电动-微生物修复技术的调控提供了理论基础和技术方法。     

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。     

一株阿维菌素降解菌AW1-18的筛选与分类鉴定

利用富集培养法从长期施用阿维菌素农药的菜豆土壤中分离出18株能利用阿维菌素为唯一碳源和氮源生长的细菌.采用紫外分光光度法对菌株的阿维菌素降解能力进行测定,结果有4株菌有较好的降解率,其中降解率最好的菌株命名为AW1-18.通过高效液相色谱法对AW1-18的降解能力进行测定,结果表明,当接种量为2.5％时,该菌株在含100 mg/L的阿维菌素无机盐基础培养液中,30℃,150 r/min,pH7的条件下培养6d后,对阿维菌素的降解率达75％以上.用16S rRNA通用引物,经PCR扩增、测序得到AW1-18的16S rRNA序列(GenBank登录号为JQ316540),在NCBI中通过BLAST后发现与不动杆菌属(Acinetobacter)的16S rRNA序列相似性达到99％,结合形态特征和生理生化特性分析结果,确定菌株AW1-18为Acinetobacter tandoii.     

聚乳酸/聚己二酸-对苯二甲酸丁二酯对土壤细菌群落结构的影响及其降解菌的筛选

【背景】近年来,聚乳酸/聚己二酸-对苯二甲酸丁二酯(polylactide/polybutyleneadipateco-terephthalate,PLA/PBAT)可降解地膜得到了广泛的使用,然而材料使用对土壤微生物的影响却鲜有报道。【目的】以新疆土壤为例,研究PLA/PBAT地膜的使用对土壤中微生物群落结构的影响;并从土壤中筛选可降解PLA/PBAT的菌株,为土壤环境的原位修复提供技术支持。【方法】采用高通量测序的方法对比使用PLA/PBAT地膜前后土壤中细菌群落的结构变化;采用筛选培养基从土壤中分离、鉴定PLA/PBAT的降解菌,通过改变不同培养条件研究菌株降解效果。【结果】使用PLA/PBAT地膜后,土壤中酸杆菌门、芽单胞菌门的相对丰度上升,变形菌门、放线菌门的相对丰度下降,这可能是地膜降解过程中其中间产物对土壤pH及微生物的抑制作用所致;并从土壤中分离出一株PLA/PBAT降解菌XJ11,初步鉴定为Delftiatsuruhatensis,在外加1.5%胰蛋白胨的PLA/PBAT (规格1×1×0.05 cm)筛选培养基中,接种菌液1 mL,在pH为7.2、37°C、130 r/min的条件下,7d内PLA/PBAT的降解率可达6.87%。【结论】PLA/PBAT地膜的使用可以改变土壤细菌群落结构,从环境中筛选出高效的PLA/PBAT降解菌成为解决地膜污染的有效措施。     

石油污染土壤中菲、蒽和正十六烷的微生物降解

在模拟自然条件下,考察了芳香烃(菲、蒽)和脂肪烃(正十六烷)单独存在以及共存于土壤中时,土著微生物对它们降解的影响。结果表明,土著微生物对它们的降解均符合一级反应动力学。菲、蒽或正十六烷单独存在于土壤中时,其微生物降解速率常数分别为0.0226、0.0283和0.0096 d^-1。菲和正十六烷共存时,正十六烷能够作为土著微生物降解菲的共代谢底物,促进菲的降解,使菲的半衰期比其单独存在于土壤中缩短44%;同时,正十六烷的加氧酶被菲诱导,使其活性提高而增强对正十六烷的降解作用,其微生物降解半衰期比其单独存在于土壤中缩短49%。菲和蒽共存促进了土著微生物对菲的降解,却抑制了对蒽的降解。     

东北羊草草原微生物在能流中作用的研究——常微分方程稳定性在能流上的应用

在东北地区天然羊草(Leymus chinesis)草原上测定了羊草凋落物生物量、热值含量和分解速率以及土壤微生物生物量的呼吸作用速率,并将测定结果换算成能量。结果指出,在土壤微生物的能量流动过程中,羊草凋落物中的能量含量为206.57千卡/平方米·年;土壤微生物分解羊草凋落物中的能量为83.79千卡/平方米·年;土壤微生物在呼吸作用中消耗的能量为20.64千卡/平方米·年;土壤微生物自身贮存的能量为63.15千卡/平方米·年。据此推算,每年积累在地表上的羊草凋落物约需2.5—3年的时间可全部分解完。用电子计算机对土壤微生物的能量流动进行了稳定性分析表明,其能量流动过程中的平衡态是渐近稳定的,说明该地土壤微生物能量流动过程中平衡态稳定性机制为负反馈机制。即当土壤微生物的能量流动过程受到干扰时,土壤微生物具有抵抗干扰和保持平衡态的自我调节能力,以确保能量流动的正常进行。     

两株微生物菌株对阿维菌素降解性能的研究CSCD

抗生素滥用问题给环境带来严重的影响,寻求一种处理环境中残余抗生素的方法至关重要。本文采用单因素法与多因素法结合的方法,测试枯草芽孢杆菌和志贺氏菌对阿维菌素的降解性能,两株细菌表现出良好的阿维菌素降解性能。随后,利用Box-Behnken design软件对实验结果进行响应面分析,继而对阿维菌素的降解条件进行优化。枯草芽孢杆菌降解阿维菌素的优化条件为温度35.43℃、装样量57.56 mL、菌种液量3.85%,此时可达到理论最大降解率59.15%;志贺氏菌降解阿维菌素的优化条件为温度30.45℃、装样量60.24 mL、菌种液量3.56%,此时可达到理论最大降解率65.34%。结果表明,枯草芽孢杆菌及志贺氏菌是降解阿维菌素的性能优良的菌株,其响应面模型确定系数均在90%以上。因此,该模型可用于分析微生物菌株对阿维菌素的降解效果,为实际中微生物菌株降解阿维菌素提供理论依据。     

不同施肥黑土微生物量氮变化特征及相关因素

研究长期施用两种不同量有机肥(M2、M4)和化肥(NPK)的黑土微生物量N在作物生长季的变化特征．结果表明,施用有机肥黑土微生物量N显著高于施用化肥(NPK)和不施肥(CK),微生物量N季节波动小．微生物量N为M4 25．52～239．12mg·kg^-1,M2 10．40～94．31mg·kg^-1．NPK6．27～87．04mg·kg^-1,CK9．15～69．81mg·kg^-1,同一处理最大值与最小值相差7～14倍．M2、NPK处理微生物量N最大值出现在抽雄吐丝期,M4处理最大值出现在拔节期,CK处理最大值出现在播种期;不同处理微生物量N的差异并未因季节变化及玉米生育时期影响而明显改变．微生物量N的动态变化与极少数黑土生物、理化特性指标动态变化显著相关;微生物量N与黑土生物、理化特性,植物氮、磷、钾有极显著的正相关关系,与土壤含水量、籽粒粗蛋白含量呈显著正相关关系．     

Comparison of extracellular enzyme activities and community composition of attached and free-living bacteria in porous medium columns

Free-living and surface-associated microbial communities in sand-packed columns perfused with groundwater were compared by examination of compositional and functional characteristics. The composition of the microbial communities was assessed by bulk DNA extraction, PCR amplification of 16S ribosomal DNA fragments, separation of these fragments by denaturing gradient gel electrophoresis, and sequence analysis. Community function was assessed by measurement of beta-glucosidase and aminopeptidase extracellular enzyme activities. Free-living populations in the aqueous phase exhibited a greater diversity of phylotypes than populations associated with the solid phase. The attached bacterial community displayed significantly greater beta-glucosidase and aminopeptidase enzyme activities per volume of porous medium than those of the free-living community. On a per-cell basis, the attached community had a significantly higher cell-specific aminopeptidase enzyme activity (1.07 x 10(-7) nmol cell(-1) h(-1)) than the free-living community (5.02 x 10(-8) nmol cell(-1) h(-1)). Conversely, the free-living community had a significantly higher cell-specific beta-glucosidase activity (1.92 x 10(-6) nmol cell(-1) h(-1)) than the surface-associated community (6.08 x 10(-7) nmol cell(-1) h(-1)). The compositional and functional differences observed between these two communities may reflect different roles for these distinct but interacting communities in the decomposition of natural organic matter or biodegradation of xenobiotics in aquifers.     

蚯蚓对细菌降解土壤中菲的作用

通过30d室内培养试验,分别研究了接种蚯蚓(E)、细菌(B)以及同时接种细菌和蚯蚓(BE)对土壤中菲降解的影响.结果表明: 在土壤中菲的初始污染浓度为50 mg*kg-1的条件下,各处理间菲的降解率差异显著,其降解率的大小顺序依次为:BE》B》E》CK(对照); 在150 mg*kg-1菲的初始污染浓度下,BE处理中菲的降解率高达98.86%,显著高于CK和E处理.B处理中细菌的双加氧酶活性在3种菲初始污染浓度下没有显著差异,而BE处理中双加氧酶的活性随着土壤中菲的初始污染浓度的升高而增加.在相同菲污染浓度下BE处理中蚯蚓体内的菲含量明显高于E处理.表明蚯蚓能够通过生物富集作用降低土壤中菲的浓度,而蚯蚓与细菌的相互作用能够进一步促进土壤中菲的降解.     

Effect of various amendments on heavy mineral oil bioremediation and soil microbial activity

To examine the effects of amendments on the degradation of heavy mineral oil, we conducted a pilot-scale experiment in the field for 105 days. During the experiment, soil samples were collected and analyzed periodically to determine the amount of residual hydrocarbons and evaluate the effects of the amendments on microbial activity. After 105 days, the initial level of contamination (7490+/-480 mg hydrocarbon kg(-1) soil) was reduced by 18-40% in amended soils, whereas it was only reduced by 9% in nonamended soil. Heavy mineral oil degradation was much faster and more complete in compost-amended soil than in hay-, sawdust-, and mineral nutrient-amended soils. The enhanced degradation of heavy mineral oil in compost-amended soil may be a result of the significantly higher microbial activity in this soil. Among the studied microbial parameters, soil dehydrogenase, lipase, and urease activities were strongly and negatively correlated with heavy mineral oil biodegradation (P<0.01) in compost-amended soil.     

Microbial degradation of phenanthrene by addition of a sophorolipid mixture

The influence of sophorolipids on microbial degradation of poorly soluble phenanthrene in liquid and soil suspension culture was evaluated in the work presented. Experiments were carried out in two parts. In the first part, important basic physico-chemical characteristics of the biosurfactant and the pollutant used were determined. The critical micelle concentration (CMC) and the solubilization ratio of the biosurfactant were found to be in a good range compared with synthetic surfactants. Also, a reduction to 71% of the detectable amount of phenanthrene was measured within 4 d in soil suspension without any biotic influence. In the second part, culture experiments were done with Sphingomonas yanoikuyae, the bacterium used throughout the work presented here with the aim to assess the toxicity of the sophorolipids on these bacteria and the effect of the surfactant on biodegradation. In exponential growth tests, no toxicity up to 1 g l(-1) sophorolipids could be detected, whereas in an agar plate test, slight growth hindrance was measured at a lower concentration of 250 mg l(-1). The above mentioned data were important for planning further experiments. In the following cultivations with liquid and soil suspension media, enhancements of the biodegradation with surfactant addition were measurable. Fluorescence measurements showed that this effect was not due to an increasing biomass, but to an augmentation of bioavailability of the phenanthrene through increasing the apparent dissolved pollutant. Surfactant addition had the consequence of decreasing the residual detectable pollutant concentration (after 36 h 0.5 compared with 2.3 mg l(-1) soil suspension) and increasing the maximal degradation rate (127 instead of 80 mg l(-1) soil suspension x 10 h). Therefore, the two main problems of biological soil remediation techniques, longer process time and residual pollutants, may be solved by the use of surfactants.     

Trichloroethylene biodegradation by mesophilic and psychrophilic ammonia oxidizers and methanotrophs in groundwater microcosms.

This study investigated the efficiency of methane and ammonium for stimulating trichloroethylene (TCE) biodegradation in groundwater microcosms (flasks and batch exchange columns) at a psychrophilic temperature (12 degrees C) typical of shallow aquifers in the northern United States or a mesophilic temperature (24 degrees C) representative of most laboratory experiments. After 140 days, TCE biodegradation rates by ammonia oxidizers and methanotrophs in mesophilic flask microcosms were similar (8 to 10 nmol day-1), but [14C]TCE mineralization (biodegradation to 14CO2) by ammonia oxidizers was significantly greater than that by methanotrophs (63 versus 53%). Under psychrophilic conditions, [14C]TCE mineralization in flask systems by ammonia oxidizers and methanotrophs was reduced to 12 and 5%, respectively. In mesophilic batch exchange columns, average TCE biodegradation rates for methanotrophs (900 nmol liter-1 day-1) were not significantly different from those of ammonia oxidizers (775 nmol liter-1 day-1). Psychrophilic TCE biodegradation rates in the columns were similar with both biostimulants and averaged 145 nmol liter-1 day-1. Methanotroph biostimulation was most adversely affected by low temperatures. At 12 degrees C, the biodegradation efficiencies (TCE degradation normalized to microbial activity) of methanotrophs and ammonia oxidizers decreased by factors of 2.6 and 1.6, respectively, relative to their biodegradation efficiencies at 24 degrees C. Collectively, these experiments demonstrated that in situ bioremediation of TCE is feasible at the psychrophilic temperatures common in surficial aquifers in the northern United States and that for such applications biostimulation of ammonia oxidizers could be more effective than has been previously reported.     

Microbial degradation of street dust polycyclic aromatic hydrocarbons in microcosms simulating diffuse pollution of urban soil

Diffuse pollution with polycyclic aromatic hydrocarbons (PAHs) of topsoil in urban regions has caused increasing concerns in recent years. We simulated diffuse pollution of soil in microcosms by spiking sandy topsoil (A-horizon) and coarse, mineral subsoil (C-horizon) with street dust (PM63) isolated from municipal street sweepings from central Copenhagen. The microbial communities adapted to PAH degradation in microcosms spiked with street dust in both A-horizon and C-horizon soils, in spite of low PAH-concentrations. The increased potential for PAH degradation was demonstrated on several levels: by slowly diminishing PAH-concentrations, increased mineralization of 14C-PAHs, increasing numbers of PAH degraders and increased prevalence of nah and pdo1 PAH degradation genes, i.e. the microbial communities quickly adapted to PAH degradation. Three- and 4-ring PAHs from the street dust were biodegraded to some extent (10-20%), but 5- and 6-ring PAHs were not biodegraded in spite of frequent soil mixing and high PAH degradation potentials. In addition to biodegradation, leaching of 2-, 3- and 4-ring PAHs from the A-horizon to the C-horizon seems to reduce PAH-levels in surface soil. Over time, levels of 2-, 3- and 4-ring PAHs in surface soil may reach equilibrium between input and the combination of biodegradation and leaching. However, levels of the environmentally critical 5- and 6-ring PAHs will probably continue to rise. We presume that sorption to black carbon particles is responsible for the persistence and low bioaccessibility of 5- and 6-ring PAHs in diffusely polluted soil.     

The abundance of nahAc genes correlates with the 14C-naphthalene mineralization potential in petroleum hydrocarbon-contaminated oxic soil layers

In this study, we evaluated whether the abundance of the functional gene nahAc reflects aerobic naphthalene degradation potential in subsurface and surface samples taken from three petroleum hydrocarbon contaminated sites in southern Finland. The type of the contamination at the sites varied from lightweight diesel oil to high molecular weight residuals of crude oil. Samples were collected from both oxic and anoxic soil layers. The naphthalene dioxygenase gene nahAc was quantified using a replicate limiting dilution-polymerase chain reaction (RLD-PCR) method with a degenerate primer pair. In the non-contaminated samples nahAc genes were not detected. In the petroleum hydrocarbon-contaminated oxic soil samples nahAc gene abundance [range 3 x 10(1)-9 x 10(4) copies (g dry wt soil)(-1)] was correlated (Kendall non-parametric correlation r2=0.459, p<0.01) with the aerobic 14C-naphthalene mineralization potential (range 1 x 10(-5)-0.1 d(-1)) measured in microcosms at in situ temperatures (8 degrees C for subsurface and 20 degrees C for surface soil samples). In these samples nahAc gene abundance was also correlated with total microbial cell counts (r2=0.471, p<0.01), respiration rate (r2=0.401, p<0.01) and organic matter content (r2=0.341, p<0.05). NahAc genes were amplified from anoxic soil layers indicating that, although involved in aerobic biodegradation of naphthalene, these genes or related sequences were also present in the anoxic subsurface. In the samples taken from the anoxic layers, the aerobic 14C-naphthalene mineralization rates were not correlated with nahAc gene abundance. In conclusion, current sequence information provides the basis for a robust tool to estimate the naphthalene degradation potential at oxic zones of different petroleum hydrocarbon-contaminated sites undergoing in situ bioremediation.     

Effect of the fuel system icing inhibitor diethylene glycol monomethyl ether on the biodegradation of jet fuel in soil

Microbial degradation of jet fuel leads to the accumulation of sludge in fuel distribution systems and storage tanks. To prevent this phenomenon, the biocidal anti-icing inhibitor diethylene glycol monomethyl ether (DiEGME) is routinely added to the fuel. The fate of DiEGME in soil and its consequent effect on the biodegradation of jet fuel by indigenous soil microflora have not been investigated. The aim of this work was to study the kinetics of biodegradation of jet fuel in dark rendzina soil, as affected by the presence of DiEGME. Our data show that the degradability in soil of jet fuel amended with DiEGME was tenfold higher than that of non-amended fuel. Consequently, there was an increase in the jet-fuel-utilizing soil microbial populations during the 100 days of incubation of soil samples amended with jet fuel containing DiEGME. Gas chromatograms of distilled fractions of jet fuel extracted from the soil demonstrated that most of the light fractions' extracts could not be detected at the end of the 100-day incubation. The relative concentration of aromatic compounds in the soil contaminated with DiEGME-amended jet fuel increased during incubation, demonstrating the lower biodegradation rate of these components compared with other fuel components. DiEGME was partially degraded by the general microbial population of the soil. Maximal DiEGME degradation was obtained with specific jet-fuel-utilizing microbial strains – Pseudomonas aeruginosa and Cladosporium resinae – that were added to a carbon-free mineral medium. The degradation rate of DiEGME by specific strains or by soil mixed populations bore an inverse relationship to the DiEGME concentration. The finding that DiEGME can be degraded by indigenous soil microorganisms may have facilitated its utilization also by jet-fuel-degrading microorganisms.     

Biomineralization of an organophosphorus pesticide,Monocrotophos, by soil bacteria

AIMS: To study biomineralization of Monocrotophos (MCP) and identify the metabolites formed during biodegradation. METHODS AND RESULTS: Two cultures, namely Arthrobacter atrocyaneus MCM B-425 and Bacillus megaterium MCM B-423, were isolated by enrichment and adaptation culture technique from soil exposed to MCP. The isolates were able to degrade MCP to the extent of 93% and 83%, respectively, from synthetic medium containing MCP at the concentration of 1000 mg x l(-1), within 8 d, under shake culture condition at 30 degrees C. The cultures degraded MCP to carbon dioxide, ammonia and phosphates through formation of one unknown compound--Metabolite I, valeric or acetic acid and methylamine, as intermediate metabolites. The enzymes phosphatase and esterase, reported to be involved in biodegradation of organophosphorus compounds, were detected in both the organisms. CONCLUSIONS:Arthrobacter atrocyaneus MCM B-425 and B. megaterium MCM B-423 isolated from soil exposed to MCP were able to mineralize MCP to carbon dioxide, ammonia and phosphates. SIGNIFICANCE AND IMPACT OF THE STUDY: Pathway for biodegradation of MCP in plants and animals has been reported. A microbial metabolic pathway of degradation involving phosphatase and esterase enzymes has been proposed. The microbial cultures could be used for bioremediation of wastewater or soil contaminated with Monocrotophos.     

Identification of dominant bacterial phylotypes in a cadmium-treated forest soil

The presence of heavy metals in soils can lead to changes in microbial community structure, characterized by the dominance of groups that are able to tolerate contamination. Such groups may provide good microbial indicators of heavy-metal pollution in soil. Through terminal restriction fragment length polymorphism (T-RFLP) profiling, changes in the bacterial community structure of an acidic forest soil that had been incubated with cadmium (Cd) for 30 days were investigated. T-RFLP revealed, in particular, three operational taxonomic units (OTUs) strongly dominating in relative abundance in the contaminated soil. By cloning of the amplified 16S rRNA genes and partial sequencing of 25 clones, these three dominant OTUs were phylogenetically characterized. One dominant OTU in the cadmium-contaminated soil was derived from Betaproteobacteria, genus Burkholderia, and the other two were from uncultured members of the class Actinobacteria, closely related to the genus Streptomyces. To confirm T-RFLP data, four primers were designed on the basis of this study's dominant sequences, targeting the OTUs corresponding to Burkholderia or Actinobacteria. Real-time PCR showed that Burkholderia target sequences were more abundant in cadmium-treated soil (7.8 x 10(7)+/- 3.0 x 10(7) targets g(-1) soil) than in untreated soil (4.0 x 10(6)+/- 8.9 x 10(5) targets g(-1) soil). It was concluded that the genus Burkholderia includes species that may be particularly dominant under cadmium contamination.