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1.
Bacterial communities associated with Moina sp. in the floodwater of a paddy field microcosm were examined by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rDNA. Eighteen out of 20 eubacterial DGGE bands were sequenced. The associated eubacterial communities mainly consisted of the Cytophaga-Flavobacterium-Bacteroides group and α-, β-, and γ-Proteobacterial groups, irrespective of the application of rice straw and rice straw compost. The effect of the application of rice straw and compost on the communities was not appreciable, compared with host specificity. An uncultured Cytophagales bacterium was estimated to be specifically associated with Moina sp. Presence of bacteria that are specific to rice straw treatment was also estimated.  相似文献   

2.
The surface of micro crustaceans collected from the overlying water of a submerged paddy soil was observed in detail by scanning electron microscopy. Epibiotic bacteria were less diverse compared to free-living bacteria in the overlying water. Specific bacteria appeared to preferentially colonize certain parts of microcrustaceans. The epibiotic bacteria, the sites they colonized and their density depended on the kinds of microcrustaceans (Moina macrocopa, Cyclopidae, Cypretta sp., and Tanycypris sp.). These results suggested the presence of significant associations in the overlying water between specific groups of bacteria and microcrustaceans.  相似文献   

3.
Bacterial communities in rice roots that developed from different nodes and at different growth stages were compared by using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA. Rice root samples were collected at three stages, namely tillering (July 2), maximum tillering (July 21), and ripening (September 12). The bacterial diversity in rice roots was found to increase along with the growth stages of the rice plants as well as the root age from the numbers of DGGE bands. The community structure of the bacteria was also found to change with the growth stages and root age from cluster analysis. Sequence analysis of the DGGE bands indicated that the dominant bacteria associated with rice roots were Gram-negative bacteria, especially β-Proteobacteria irrespective of the growth stages and root age. DGGE bands related to Janthinobacterium agaricidamnosum W1r3T and Clostridium sp. FCB90-3 were ubiquitous in many roots irrespective to the sampling date. Principal component analysis enabled to characterize the DGGE bands related to nitrogen-fixing Azoarcus spp., and Azovibrio sp. BS20-3 in the samples collected on July 2 and on July 21, and the myxobacteria collected on September 12, respectively, as representative bacteria in the bacterial communities. The habitat around older rice roots at every sampling date was more reductive than that around younger rice roots, and the DGGE bands related to Spirochaeta spp. were specific in older roots at every sampling date. Some specific bacteria that were most closely related to the DGGE bands were found from principal component analysis to characterize young and old. roots at each growth stage as follows: aerobes Flavobacterium sp. 90 clone 2 and Janthinobacterium agaricidamnosus W1r3T in young roots and facultative anaerobes Dechloromonas sp. MissR and Anaeromyxobacter dehalogenans 2CP-3 in old nodal roots on July 2, strict anaerobe Geobacter pelophilus Dfr2 and aerobes Nitrosospira sp. Nsp17 and uncultured Nitrospira sp. clone 4-1 in old roots on July 21, and different Clostridium spp. in both young and old roots and Desulfovibrio magneticus RS-1 in old roots on September 12, respectively. A larger number of the closest relatives of anaerobic bacteria grew at the late stage than at the early stages, and in old roots than in younger roots. Thus, the environment of paddy roots was remarkably heterogeneous as a bacterial habitat, where not only the whole root system but also a root may create oxic and anoxic environments.  相似文献   

4.
Abstract

The phylogenetic positions of bacterial communities in manganese (Mn) nodules from subsoils of two Japanese rice fields were estimated using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis followed by sequencing of 16S rDNA. The DGGE band patterns and sequencing analysis of characteristic DGGE bands revealed that the bacterial communities in Mn nodules were markedly different from those in the plow layer and subsoils. Three out of four common bands found in Mn nodules from two sites corresponded to Deltaproteobacteria and were characterized as sulfate-reducing and iron-reducing bacteria. The other DGGE bands of Mn nodules corresponded to sulfate and iron reducers (Deltaproteobacteria), methane-oxidizing bacteria (Gamma and Alphaproteobacteria), nitrite-oxidizing bacteria (Nitrospirae) and Actinobacteria. In addition, some DGGE bands of Mn nodules showed no clear affiliation to any known bacteria. The present study indicates that members involved in the reduction of Mn nodules dominate the bacterial communities in Mn nodules in rice field subsoils.  相似文献   

5.
Soil microbial biomass and community structures are commonly used as indicators for soil quality and fertility. A investigation was performed to study the effects of long-term natural restoration, cropping, and bare fallow managements on the soil microbial biomass and bacterial community structures in depths of 0--10, 20--30, and 40--50 cm in a black soil (Mollisol). Microbial biomass was estimated from chloroform fumigation-extraction, and bacterial community structures were determined by analysis of 16S rDNA using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Experimental results showed that microbial biomass significantly declined with soil depth in the managements of restoration and cropping, but not in the bare fallow. DGGE profiles indicated that the band number in top 0--10 cm soils was less than that in depth of 20--30 or 40--50 cm. These suggested that the microbial population was high but the bacterial community structure was simple in the topsoil. Cluster and principle component analysis based on DGGE banding patterns showed that the bacterial community structure was affected by soil depth more primarily than by managements, and the succession of bacterial community as increase of soil depth has a similar tendency in the three managements. Fourteen predominating DGGE bands were excised and sequenced, in which 6 bands were identified as the taxa of Verrucomicrobia, 2 bands as Actinobacteria, 2 bands as α-Proteobacteria, and the other 4 bands as δ-Proteobacteria, Acidobacteria, Nitrospira, and unclassified bacteria. In addition, the sequences of 11 DGGE bands were closely related to uncultured bacteria. Thus, the bacterial community structure in black soil was stable, and the predominating bacterial groups were uncultured.  相似文献   

6.
Percolating water was sampled from the plow layer and subsoil layer in a Japanese paddy field, and the bacterial communities were compared together with floodwater by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) targeting a partial 16S rRNA gene and subsequent sequencing. The number of DGGE bands ranged from 16 to 28 with no significant differences among the sampling sites and times. Only 2 bands were common for the three sources of water samples. DGGE bands specific for the floodwater samples and percolating water samples from the plow layer were identified, while percolating water samples from the subsoil layer did not show specific bands but displayed common bands to those of the floodwater samples (7 bands) and percolating water samples from the plow layer (1 band). Cluster analysis of the DGGE banding patterns showed a distinct clustering in the samples of percolating water from the plow layer and a closer relationship between the others. These results suggest that the bacterial communities in percolating water changed during downward movement through the plow layer and subsoil layer. Sequences of the DGGE bands specific for the samples of percolating water from the plow layer showed a close relationship with anaerobic bacteria such as iron-reducers or uncultured bacterial DNA isolated from environments that are considered to be less oxic. On the other hand, the sequences of the bands specific for the samples of floodwater and percolating water from the subsoil layer showed a close relationship with uncultured bacterial DNA isolated from freshwater environments.  相似文献   

7.
The effect of free-air CO2 enrichment (FACE) on the methanogenic archaeal communities inhabiting rice roots was studied in a Japanese rice field by separately collecting rice roots three times (at mid-tillering, panicle initiation, and heading stages) according to their nodal number, extracting DNA from the roots and subjecting it to polymerase-chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and sequence analyses. Appearance of roots indicated that aging and senescence occurred faster under the FACE conditions than under the ambient conditions. The number of DGGE bands of methanogenic archaeal communities tended to increase with the growth stages. Cluster analysis showed that the succession of methanogenic archaeal communities in the ambient plot preceded that in the FACE plot, while the trend of the appearance of rice roots was opposite. All the closest relatives associated with the DGGE bands belonged to Methanomicrobiales and Rice cluster I, and FACE did not affect the phylogenetic position of the closest relatives associated with the characteristic DGGE bands. Faster succession of methanogenic archaeal communities in the ambient plot and similar phylogenetic members between the plots were observed in rice roots in years with both warmer (1999) and cooler (2003) weather during the rice cultivation period than in average years.  相似文献   

8.
PCR-DGGE analysis followed by sequencing was conducted to estimate the succession and the phylogenetic profile of the eubacterial communities responsible for the decomposition of rice straw (RS) that was incorporated into a rice field. Leaf sheath and leaf blade parts were separately put in nylon mesh bags, and were placed in the rice field soil under drained conditions during the off-cropping season and under flooded conditions after transplantation of rice. In addition, RS samples that had been placed under drained conditions in the off-cropping season were placed again in flooded rice field soil after transplantation of rice. DGGE patterns of the bacterial communities in the RS samples were classified into two groups, namely leaf sheaths and leaf blades. Principal component analysis of the DGGE patterns revealed the succession along with the duration of placement. These results indicated that the RS part (sheath or blade) mainly determined the structure of the bacterial communities responsible for the RS decomposition, followed by the duration of placement. Sequence analysis of the characteristic DGGE bands indicated that most of the closest relatives associated with the bands belonged to α-, β-, γ-, and δ-Proteobacteria, CFB group, and Spirochaetes. Some bands were closely related to Acidobacteria and Verrucomicrobia. CFB members and α-Proteobacteria predominated commonly in both RS parts, while γ- and δ-Proteobacteria, and Spirochaetes and β-Proteobacteria specifically colonized sheath and blade parts, respectively. In addition, Proteobacteria and CFB members characterized the differences in the bacterial communities under flooded or drained conditions. These results suggest that Proteobacteria, CFB group, and Spirochaetes were responsible for RS decomposition in rice field soil under both flooded and drained conditions.  相似文献   

9.
As limited information is available about the relationship between microbial processes and community structure in tropical soils, we used 15N-DNA stable isotope probing (15N-DNA-SIP) to identify bacteria actively involved in decomposition of plant residues of different biochemical quality. 15N-labeled (90 atom%) and unlabeled (control) maize (C-to-N ratio: 32; cellulose content: 24.9%) and soybean (15; 15.5%) leaf residues were incubated in a tropical Vertisol for 15 days. Soil DNA was isolated, subjected to 15N-DNA-SIP and buoyant density-resolved DNA fractions were analyzed by 16S rRNA gene-based denaturing gradient gel electrophoresis (DGGE) analysis and sequencing of selected DGGE bands. Residue addition induced new bands and changed relative intensity of already existing bands in 15N-enriched SIP fractions. Phylogenetic analysis of selected, cloned DGGE bands from ‘heaviest’ 15N-enriched fractions (57.8 atom% (maize), 87.1 atom% (soybean)) revealed that soils treated with maize residues were dominated by Pseudonocardia sp., while Arthrobacter sp. and Streptomyces sp. were found in the soybean residue treated soils. Sequences related to Bacillus sp. and Saccharopolyspora sp. were found in both organic residue treatments. Our study gave clear evidence that 15N-DNA-SIP combined with 16S rRNA gene-based community fingerprinting of density-resolved fractions and an unlabeled control was suited for detecting active bacteria involved in decomposition of complex maize and soybean residues. In conclusion, we could show that residue quality, inducing contrasting N assimilation by decomposing bacteria, was a substantial determinant of certain decomposing community members assayed in this study.  相似文献   

10.
Three experiments were conducted in this study in order to investigate the impacts of soil type, soybean genotype, and the reproductive growth stage on bacterial communities in the soybean rhizosphere. Communities were evaluated by principal component analysis of denaturing gradient gel electrophoresis (DGGE) banding patterns and sequencing of partial 16S rDNA polymerase chain reaction (PCR) amplicons. A pot experiment analyzing three soybean genotypes grown in two different types of soil (Black soil and Dark Brown soil) indicated that soil type was the major factor in influencing the bacterial communities in the soybean rhizosphere, with a more significant effect observed in the Black soil samples than in the Dark Brown soil samples. A field experiment was conducted in Dark Brown soil using three soybean genotypes, and the results gleaned from both pot and field experiments indicated that bacterial communities in the soybean rhizosphere changed with growth stages, and higher number of DGGE bands observed in early reproductive growth stages, while surprisingly, a significant impact of genotype on the bacterial communities was not observed in these experiments. However, a plate culture experiment targeting the culturable bacterial communities detected a remarkable difference in the community structures of the rhizosphere between the two soybean genotypes, suggesting that a small portion of the total bacteria was influenced by genotype. Sequence analysis of DGGE bands indicated that bacterial phyla of Proteobacteria, Actinobacteria, Bacteroidetes, Nitrospirae, Firmicutes, Verrucomicrobia and Acidobacteria commonly inhabit the soybean rhizosphere.  相似文献   

11.
The diversity of endobacteria associated with ectomycorrhizas of Suillus variegatus and Tomentellopsis submollis, in two Corsican pine (Pinus nigra) stands was analysed by cultivation-dependent and cultivation-independent molecular methods. Denaturing gradient gel electrophoresis (DGGE) analysis revealed the cultivable endobacterial communities associated with S. variegatus were similar within the same stand. The most abundant cultivable bacterial species belonged to the genera Pseudomonas and Burkholderia. Cultivation-independent molecular analysis indicated that the structure of the endobacterial communities in ectomycorrhizas was consistent across all samples regardless of ECM fungal species or the pine stand from which the samples were collected. However, comparison between rDNA- and rRNA-derived DGGE gels showed that metabolically active endobacterial species were not always detected in rDNA-based profiles. Clone libraries constructed from rRNA molecules indicated that Pseudomonas and Burkholderia spp. were metabolically active bacteria. As some of the most abundant cultivable bacteria, including Bacillus/Paenibacillus spp., were not detected in cultivation-independent DGGE profiles, a combination of cultivation-dependent and -independent approaches provided a more complete assessment of the diversity of endobacteria associated with ectomycorrhizas.  相似文献   

12.
To estimate the succession and phylogenetic composition of the bacterial communities responsible for the decomposition of rice straw compost under flooded conditions during the cultivation period of paddy rice, denaturing gradient gel electrophoresis (DGGE) analyses targeting 16S rDNA and 16S rRNA, followed by sequencing were conducted in a Japanese paddy field. The DGGE bands of the bacterial communities in the rice straw compost were significantly more numerous in the DNA samples than in the RNA samples. Although the band number of the DNA samples was almost constant throughout the period, RNA samples showed fewer DGGE bands after mid-season drainage than before it. Thus, about 81% of the bacteria present in rice straw compost were considered to be metabolically "active" before mid-season drainage and about 62% after it. The changes in the DGGE patterns of bacterial DNA and RNA before and after mid-season drainage, respectively, were also revealed by cluster analysis and principal component analysis of the DGGE patterns. These results indicated that the bacterial communities of rice straw compost incorporated into flooded paddy fields changed gradually along with the decomposition, except for the period of mid-season drainage, but that they were influenced by mid-season drainage. Members of β-, γ- and δ-Proteobacteria, Cytophaga-Flavobacterium-Bacteroides (CFB) group, Chlorobia, Verrucomicrobia, Chloroflexi, Spirochaetes, Firmicutes (clostridia) and Actinobacteria were present during the decomposition of rice straw compost. Characteristic "active" bacteria among them were as follows: Clostridium, Acinetobacter (γ-Proteobacteria) and β-Proteobacteria before mid-season drainage, Flavobacterium, Chondromyces , Chlorflexi and δ-Proteobacteria after mid-season drainage, and Spirochaeta and myxobacteria throughout the period.  相似文献   

13.
Culture-dependent DGGE (CD DGGE) fingerprinting of the 16S rRNA gene was used to characterize mixed bacterial communities recovered on agar plates. Using R2A Agar as a growth medium, CD DGGE analysis resulted in clear banding patterns of sufficient complexity (16-32 major bands) and reproducibility to investigate differences in bacterial communities in a silt loam soil. Replicate CD DGGE profiles from plates inoculated with less-dilute samples (10−3) had a higher band count and were more similar (72-77%) than profiles from more-dilute samples (51-61%). Different culture media and incubation conditions resulted in distinct community fingerprints and increased the cumulative number of unique bands detected. When CD DGGE fingerprints were compared to profiles constructed from 16S rRNA genes obtained from culture-independent clone libraries (CB DGGE profiles) 34% of the bands were unique to the culture-dependent profiles, 32% were unique to the culture-independent profiles and 34% were found in both communities. These data demonstrate that culture-independent DGGE profiles are supplemented by the distinct bands detected in culture-dependent profiles. CD DGGE can be a useful technique to follow the dynamics of distinct culturable fractions of the soil bacterial community.  相似文献   

14.
利用可培养和变性梯度凝胶电泳(DGGE)方法,对经不同浓度TiO2处理黄瓜(Cucumis sativus)叶围细菌群落结构的变化进行了分析。研究发现,TiO2处理后黄瓜叶围可培养细菌数量较对照显著降低。随着TiO2浓度从0.02 mg/mL提高至20 mg/mL,黄瓜叶围可培养细菌数量从1.8×107 cfu/g降低至3.1×106 cfu/g。DGGE指纹图谱分析表明,当TiO2的喷雾浓度超过0.02 mg/mL时,黄瓜叶围细菌的多样性显著降低。对DGGE条带克隆测序结果显示,在黄瓜叶围至少存在7种不同属的细菌,其中只有一种叶围细菌不受TiO2喷雾浓度影响。  相似文献   

15.
We assessed the Azospirillum inoculation and N-fertilization effect on grain yield and on the phyllosphere endophytic diversity of nitrogen-fixing bacteria in a rice rainfed crop. We used cultivation-based techniques and cultivation-independent methods involving PCR-16S rRNA and denaturing gradient gel electrophoresis (DGGE). In general, we observed that grain yield was improved when inoculated with Azospirillum (depending on the genotype) and/or fertilized with urea. A similar behavior was observed in total N-content in grain and the MPN determination, as the highest values occurred when seeds were inoculated with A. brasilense REC3 (S1) than with A brasilense 13-2C (S2). A positive nitrogenase activity and PCR-nifH amplification suggests that the bacteria associated to inner tissues of rice phyllosphere could have contributed to the different N-contents detected. The bacterial diversity, observed in the number and intensity of DGGE profiles, showed a higher number of bands when total DNA was obtained using only CTAB than with CTAB + PVP. The DGGE profiles revealed great stability in the dominating bands, which presumably represent numerically dominant species. Application of A. brasilense strains as inoculants did not influence the dominant members of the endophytic microbial communities in the phyllosphere, but improved N-content and production of rainfed rice crop.  相似文献   

16.
Bacterial communities at different habitats in a Japanese paddy field ecosystem were compared to understand the bacterial world in the ecosystem as a whole by analyzing data of the denaturing gradient gel electrophoresis (DGGE) band patterns and the sequenced DGGE bands. The habitats were floodwater, percolating water, microcrustacean inhabiting in floodwater, plow layer soil, rice roots, rice straw and rice straw compost incorporated in soil, rice straw placed on the soil surface, plant residues in paddy fields, and rice straw under composting process. Phylotype (band) richness, diversity, evenness, and stability of the bacterial communities at the respective habitats were evaluated based on the DGGE profile data. Phylotype richness was greater near plant residues, rice straw buried in soil and rice straw placed on soil surface, while it was smaller at microcrustacean and rice straw compost buried in soil. The samples from plow layer soil and rice straw compost buried in soil showed considerably higher index values for diversity, evenness, and stability, while those from rice straw placed on soil surface and microcrustacean had lower values of the indices than other habitats. Sequences of totally 250 DGGE bands were assigned to phyla or classes. Distribution of bacterial members to phylogenetic taxa was different among the respective habitats. Inhabitants in plow layer soil were most widely distributed among the groups (nine phyla: Proteobacteria, Chloroflexi, Chlorobi, Verrucomicrobia, Acidobacteria, Nitrospira, candidate division OP10, Cyanobacteria, and Actinobacteria), while those in floodwater and microcrustacean were restricted to only three phyla (Proteobacteria, Bacteroidetes, and Actinobacteria). Proteobacteria and Bacteroidetes were found at all the habitats and the habitats except for plow layer soil, respectively, whereas abundant members belonged to Chloroflexi and Actinobacteria in plow layer soil. “Comprehensive mapping” of DGGE fragments was conducted by principal component analysis based on evolutionary distances of the fragments to 202 reference bacterial strains to overview phylogenetic relationships of bacterial members among the respective habitats. The score plots with the first and second principal components distinctly characterized bacterial members at the respective habitats, and the similarity between the respective communities was clearly demonstrated. Overall, bacterial communities at the respective habitats were distinct and different in the diversity and stability to each other, which may have contributed to the diversity of overall bacterial communities in the paddy field ecosystem.  相似文献   

17.
Thirteen copper-resistant bacteria were isolated from copper-tolerant plant species growing on a copper mine wasteland. The isolates were identified by 16S rRNA gene sequence analysis and characterized by their resistance to heavy metals and plant growth-promoting characteristics. The assessment of the bacterial communities in the rhizosphere soils of copper-tolerant plants was measured as bands in denaturing gradient gel electrophoresis (DGGE) obtained directly from rhizosphere soil DNA extracts. The isolates were found to exhibit different multiple heavy metal resistance characteristics. Strains SZY6, YJ7 and JYC17 were found to produce indole acetic acid (IAA), siderophore, 1-aminocyclopropane-1-carboxylate (ACC) deaminase or to solubilize phosphate. Root elongation assay conducted on rape under gnotobiotic conditions with strains MT16, JYC17, SZY6, GZC24, and YJ7 demonstrated increase (from 16 to 41%) in root elongation of inoculated rape seedlings compared to the control plants. In the rhizosphere soil samples the DGGE profiles of the direct DNA extracts were similar. The DGGE profiles indicated that there was no significant correlation between the concentration of available copper in the rhizosphere soils and the number of the visible bands in the DGGE pattern.  相似文献   

18.
以养殖废水沼气池沼泥为接种物,构建了乙二胺、三氯化铁改性阳极的无介体单室微生物燃料电池（MFC）体系,均成功实现了连续产电,同时对废水中的污染物也具有很好的去除效果。为了更好地研究微生物燃料电池阳极生物膜的微生物多样性,分别采集了两种MFC阳极生物膜样品,采用PCR-DGGE法研究了一个完整产电周期的启动期（S）、葡萄糖产电稳定期（RG）和养殖废水原水稳定期（RS）的MFC阳极生物膜的微生物群落变化。结果表明,不同时期MFC阳极生物膜的微生物多样性存在明显差异,S-RG、S-RS、RG-RS的微生物群落相似性分别为70.1%、42.0%和50.6%。两种不同阳极富集的生物膜微生物群落相似性仅为48%,这表明不同改性方法所得的阳极对微生物具有选择性作用。对DGGE条带测序和比对发现,不同时期阳极生物膜上优势微生物包括Trichococcus sp.、Thauera sp.、Azoarcus sp.、Azospirillum sp.、Zobellella sp.、Pseudomonas sp.、Aeromonas sp.、Thiobacillus sp.、Desulfovibrio sp.、Thiomonas sp.,其中Pseudomonas sp.、Aeromonas sp.和Desulfovibrio sp.与已报道的相关产电微生物具有较高的序列相似度,这些菌种可能是本MFC体系中的主要产电菌。  相似文献   

19.
Soil properties and agricultural practices take a joint effect on the communities of soil bacteria. The aim of the present study was to survey Alphaproteobacterial communities as possible indicators of soil quality considering clay, loamy and sandy soils under conventional and organic farming. Alphaproteobacteria community composition were analysed by 16S rRNA gene with nested-PCR (polymerase chain reaction) and denaturing gradient gelelectrophoresis (DGGE). Sequencing of partial 16S rRNA gene from the DGGE bands were performed. Conventional and organic farming resulted in significant differences in chemical properties of soils. According to the results community fingerprints were separated into groups depending on soil types and farming systems. This separation can be attributed mostly to soil pH, AL-P2O5,-K2O. The analysed sequences were identified as soil bacteria which could play the main role in nitrogen fixing, mineralisation and denitrification. The highest diversity index was revealed from the organic farming at sandy texture site, where mainly Mesorhizobium sp. and Rhizobium sp. were detected. The soil type and actual crop could have a stronger impact on the soil bacterial composition than the management.  相似文献   

20.
采用稀释平板培养法与PCR-DGGE技术, 以阿维菌素为阳性对照, 水为阴性对照, 研究了大田喷施推荐剂量(0.1 kg·hm-2)和高剂量(10 kg·hm-2)苏云金芽孢杆菌(Bt)菌剂对棉花根际土壤细菌种群数量及结构的影响。结果表明, 喷雾处理后1~3 d, 不同处理组土壤细菌数量间无显著性差异, 在3 d时细菌数量均值达到最大, 之后开始下降, 12 d后清水对照、推荐剂量Bt菌剂、高剂量Bt菌剂处理组土壤细菌数量均值维持在4.0×107 CFU·g-1左右; 推荐剂量Bt菌剂处理样品土壤细菌数量在6 d时显著高于清水对照, 其余时间与清水对照间无显著性差异; 高剂量Bt菌剂处理与清水对照在整个试验期间均无显著性差异; 阿维菌素处理组土壤细菌数量在0~6 d内与清水对照无显著性差异, 而在12~45 d内显著低于其他3个处理组。DGGE图谱显示, Bt菌剂处理对棉花根际土壤17种细菌均无显著抑制作用。聚类分析结果表明, Bt菌剂对土壤细菌群落结构的扰动在12 d后得到恢复。与阴性对照组相比, Bt菌剂对土壤细菌多样性指数无显著影响, 而阳性对照阿维菌素对土壤细菌种群消长和多样性指数有较强的影响。对DGGE图谱中17条电泳条带的序列分析, 证明棉花根际土壤中存在起固氮作用的慢生根瘤菌属细菌和具有污染修复与净化活性的鞘脂菌属、鞘氨醇单胞菌属和红球菌属细菌。Bt菌剂与阿维菌素处理均对这些土壤有益菌群无明显不利影响。总体结果表明, Bt菌剂无论是在正常推荐剂量下还是在较高剂量(推荐剂量的100倍)下使用, 对棉花根际土壤微生态环境产生的冲击都较小, 是一种生态安全性较高的生物农药。  相似文献   

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