Dynamics of fungal communities in bulk and maize rhizosphere soil in the tropics

The fungal population dynamics in soil and in the rhizospheres of two maize cultivars grown in tropical soils were studied by a cultivation-independent analysis of directly extracted DNA to provide baseline data. Soil and rhizosphere samples were taken from six plots 20, 40, and 90 days after planting in two consecutive years. A 1.65-kb fragment of the 18S ribosomal DNA (rDNA) amplified from the total community DNA was analyzed by denaturing gradient gel electrophoresis (DGGE) and by cloning and sequencing. A rhizosphere effect was observed for fungal populations at all stages of plant development. In addition, pronounced changes in the composition of fungal communities during plant growth development were found by DGGE. Similar types of fingerprints were observed in two consecutive growth periods. No major differences were detected in the fungal patterns of the two cultivars. Direct cloning of 18S rDNA fragments amplified from soil or rhizosphere DNA resulted in 75 clones matching 12 dominant DGGE bands. The clones were characterized by their HinfI restriction patterns, and 39 different clones representing each group of restriction patterns were sequenced. The cloning and sequencing approach provided information on the phylogeny of dominant amplifiable fungal populations and allowed us to determine a number of fungal phylotypes that contribute to each of the dominant DGGE bands. Based on the sequence similarity of the 18S rDNA fragment with existing fungal isolates in the database, it was shown that the rhizospheres of young maize plants seemed to select the Ascomycetes order Pleosporales, while different members of the Ascomycetes and basidiomycetic yeast were detected in the rhizospheres of senescent maize plants.     

环贵州喀斯特高原湖泊环境中的细菌多样性

采用纯培养方法,选用6种培养基对23份环贵州喀斯特高原湖泊环境土壤样品中的细菌进行分离培养,经初步形态排重后共获得83株细菌纯培养物。菌株的16S rRNA基因序列信息显示,这些菌株归属于3门12目15科19属,优势细菌类群为链霉菌属（Streptomyces）、芽胞杆菌属（Bacillus）、短芽胞杆菌属(Brevibacillus）和北里孢菌属（Kitasatospora）。同时采用高通量测序分析的方法评估了这些土壤样品中的细菌群落结构特征。环境样品中16S rRNA基因的V3~V4区序列分析显示,从土壤样品中检测到分属于17门36目74科130属的细菌,涵盖喀斯特高矿物质环境、盐碱湖泊环境、森林土壤环境中存在的优势菌群,其中变杆菌属(Variibacter)、慢生根瘤菌属(Bradyrhizobium)以及嗜酸栖热菌属（Acidothermus）为优势属,体现出该生境中细菌群落结构的独特性。综合纯培养和高通量测序分析结果,环贵州喀斯特高原湖泊环境样品中细菌群落特征和环境之间存在着明显相关性,其中蕴含着丰富的细菌资源,值得进一步挖掘。     

Bacterial diversity of the rhizosphere of maize (Zea mays) grown in tropical soil studied by temperature gradient gel electrophoresis

The bacterial diversity and population dynamics in the rhizosphere of two maize cultivars (Nitroflint and Nitrodent) grown in tropical soils was studied, by traditional cultivation techniques and 16S rRNA gene-based molecular analysis of DNA directly extracted from soil and rhizosphere samples. Rhizosphere and soil samples were taken at three different plant growth stages. Total aerobic bacterial counts were determined. Fingerprints of the most dominant bacterial population were generated by TGGE separation of 16S rRNA gene fragments amplified from total community DNA using eubacterial specific primers. To reduce the complexity of TGGE fingerprints or to analyse less abundant populations, primers specific for different phylogenetic groups have been used. A comparison of the cfu obtained for rhizosphere of both cultivars indicated significant differences only for rhizosphere and soil samples taken 40 days after sowing. However, a comparison of TGGE patterns indicated that the composition of the bacterial community analysed at different plant growth stages for both cultivars was similar. A comparison of -, -proteobacterial and actinomycete TGGE patterns of both cultivars confirmed this observation. The eubacterial TGGE profiles reflected strong seasonal population shifts in the bacterial rhizosphere community of both maize cultivars which could be also observed in the TGGE patterns of - and -proteobacteria and to a lesser extent for actinomycetes. The rhizosphere effect was much more pronounced for young roots compared to samples taken from mature maize plants. The rhizosphere fingerprints showed a reduced complexity for young plants with up to five dominating bands while for mature plants patterns similar to those of soil were observed. Sequencing of dominant clones indicated that the dominant population found at all plant growth stages can be assigned to Arthrobacter populations.     

Bacterial diversity in the rhizosphere of Proteaceae species

The Cape Floral Kingdom is an area of unique plant biodiversity in South Africa with exceptional concentrations of rare and endemic species and experiencing drastic habitat loss. Here we present the first molecular study of the microbial diversity associated with the rhizosphere soil of endemic plants of the Proteaceae family (Leucospermum truncatulum and Leucadendron xanthoconus). Genomic DNA was extracted from L. truncatulum rhizosphere soil, L. xanthoconus rhizosphere and non-rhizosphere soil and used as a template for the polymerase chain reaction (PCR) amplification of the 16S ribosomal RNA gene (rDNA). Construction and sequencing of 16S rDNA libraries revealed a high level of biodiversity and led to the identification of several novel bacterial phylotypes. The bacterial community profiles were compared by 16S rDNA denaturing gradient gel electrophoresis (DGGE). Cluster analysis and biodiversity indices revealed that the rhizosphere soil samples were more similar to each other than to non-rhizosphere soil and the rhizosphere soil contained a bacterial diversity that was richer and more equitable compared with non-rhizosphere soil. A Chloroflexus and an Azospirillum genospecies were restricted to the L. xanthoconus rhizosphere soil and Stenotrophomonas genospecies was identified in all rhizosphere soil samples but was not present in the non-rhizosphere soil. Taxon-specific nested PCR and DGGE-identified differences between the Proteaceae plant rhizosphere soil with a Frankia genospecies restricted the L. truncatulum rhizosphere. Archaea-specific rDNA PCR, DGGE and DNA sequencing revealed that Crenarcheote genospecies were excluded from the plant rhizosphere soil and only present in non-rhizosphere soil.     

紫云英根际微生物碳源利用多样性研究

为探究绿肥根际调控效果的原因,采用碳素利用法-BIOLOG生态版,分析紫云英根际微生物种群结构和功能多样性。结果表明:紫云英根际土壤微生物总活性比非根际高,其主要贡献者是以氨基酸、糖类、酯类和醇类四大碳源为生的微生物,而与以磷酸盐、羧酸和胺类为碳源的微生物关系不大。进一步分析发现:紫云英根际产生了以α-酮丁酸、2-羟基安息香酸、4-羟基安息香酸、D-半乳糖醛酸、α-环式糊精、D-木糖、β-甲基-D-葡萄糖、D-甘露醇和L-精氨酸作为碳源的新微生物种群,完全抑制了以γ-羟基丁酸和苯乙基胺为碳源的微生物种群活性;根泌物抑制了以D-苹果酸、衣康酸和肝糖为碳源的微生物活性,而对以D-化纤二糖、N-乙酰基-D-葡萄胺、丙酮酸甲酯、吐温40、吐温80、L-苯基丙氨酸、L-天门酰胺酸和腐胺为碳源的微生物有促进作用,但对以D-氨基葡糖酸、α-D-乳糖和I-赤藻糖醇为碳源的微生物活性无显著影响;另外,即使是以同一类物质为碳源的微生物种群,在紫云英根际的表现也不完全一样,如以D-乳酸γ-内酯和L-丝氨酸为碳源的可快速培养微生物受到抑制,可慢速培养的微生物活性则有提高,而以甘氨酰基-L-谷氨酸为碳源的微生物的表现正好与之相反。     

Bacterial diversity in the bulk soil and rhizosphere fractions of Lolium perenne and Trifolium repens as revealed by PCR restriction analysis of 16S rDNA

The rhizosphere of Trifolium repens and Lolium perenne was divided into three fractions: the bulk soil, the soil adhering to the roots and the washed roots (rhizoplane and endorhizosphere). After isolation and purification of DNA from these fractions, 16S rDNA was amplified by PCR and cloned to obtain a collection of 16S rRNA genes representative of the bacterial communities of these three fractions. The genes were then characterized by PCR restriction analysis. Each different profile was used to define an operational taxonomic unit (OTU). The numbers of OTUs and the numbers of clones among these OTUs allowed to calculate a diversity index. The number of OTUs decreased as root proximity increased and a few OTUs became dominant, resulting in a lower diversity index. In the root fraction of T. repens, the restriction profile of the dominant OTU matched the theoretical profile of the 16S rRNA gene of Rhizobium leguminosarum. This study showed that plant roots create a selective environment for microbial populations.     

纳米银对潮土玉米根际真菌群落结构和多样性的影响

根际真菌是土壤生态系统的重要组成部分,本研究采用土壤盆栽方法,以纳米银(silver nanoparticles,Ag NPs)为研究对象,利用Illumina高通量测序技术对不同Ag NPs施加水平下(0.025、0.25、2.5mg/kg)潮土玉米根际真菌群落结构进行分析。结果表明,潮土玉米根际土壤真菌群落主要由子囊菌门Ascomycota、担子菌门Basidiomycota、芽枝菌门Blastodimycota、壶菌门Chytridiomycota、球囊菌门Glomeromycota和接合菌门Zygomycota等组成,其中以子囊菌门真菌为优势类群。Ag NPs在2.5mg/kg施加水平下显著降低了(P0.05)玉米根际土壤溶解性有机碳(DOC)含量,改变了根际土壤真菌群落结构,使真菌群落结构发生显著分异(P0.05),主要表现为降低了根霉菌属Rhizopus、镰刀菌属Fusarium、被孢霉属Mortierella等的相对丰度。相关性分析表明土壤DOC含量的变化与Ag NPs处理下根际土壤真菌群落结构分异存在显著的(P0.05)相关性。     

烟草根际土壤真菌多样性的研究

烟草土传病害发生普遍,危害严重。为深入了解烟草根际土壤真菌区系与土传病害间的相互关系,选取黑龙江、山东、广西和云南四省区的代表性烟田,开展了烟草根际土壤真菌多样性的研究。对采自上述四省区12个县市的224份烟草根际土壤样品进行了真菌的分离和培养,共分离获得1,278株真菌,通过形态学特征鉴定出真菌25属86种。其中接合菌门4属6种,子囊菌门1属1种,无性型真菌20属79种。通过分析发现,烟草根际土壤中的优势真菌种群及其菌株数量所占分离真菌总菌株数量的比例分别为：青霉属Penicillium 16.74%,木霉属Trichoderma 14.32%,镰孢菌属Fusarium 13.54%和曲霉属Aspergillus 11.50%。在12个采样地点中,山东诸城的多样性指数（H￠=2.0666）和均匀度指数（J=0.6898）最高,云南玉溪的丰富度指数（R=4.0687）最高。不同采样地点的烟草根际土壤真菌种群的相似性水平也存在差异,其中云南永胜和大理的烟草根际土壤真菌种群的相似性系数最高（Cj=0.9375）,山东沂水和云南玉溪间的相似性最低（Cj=0.5217）。     

Microbial community composition and functional diversity in the rhizosphere of maize

This study investigates the small-scale stratification of bacterial community composition and functional diversity in the rhizosphere of maize. Maize seedlings were grown in a microcosm with a horizontal mesh (53 M) creating a planar root mat and rhizosphere soil. An unplanted microcosm served as control. Thin slices of soil were cut at different distances from the mesh surface (0.2–5.0 mm) and analysed for bacterial community composition by PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) of 16S rDNA and tested for activities of different enzymes involved in C, N, P and S cycling. Bacterial community composition and microbial functional diversity were affected by the presence of the maize roots. The bacterial composition showed a clear gradient up to 2.2 mm from the root surface, while no such gradient was observed in the unplanted pot. Invertase and phosphatase activities were higher in the close vicinity of maize roots (0.2–0.8 mm), whereas xylanase activity was unaffected. This study shows that the changes in bacterial community composition and functional diversity induced by roots may extend several millimetres into the soil.     

Bacterial diversity in Fe‐rich hydrothermal sediments at two South Tonga Arc submarine volcanoes

Seafloor iron oxide deposits are a common feature of submarine hydrothermal systems. Morphological study of these deposits has led investigators to suggest a microbiological role in their formation, through the oxidation of reduced Fe in hydrothermal fluids. Fe‐oxidizing bacteria, including the recently described Zetaproteobacteria, have been isolated from a few of these deposits but generally little is known about the microbial diversity associated with this habitat. In this study, we characterized bacterial diversity in two Fe oxide samples collected on the seafloor of Volcanoes 1 and 19 on the South Tonga Arc. We were particularly interested in confirming the presence of Zetaproteobacteria at these two sites and in documenting the diversity of groups other than Fe oxidizers. Our results (small subunit rRNA gene sequence data) showed a surprisingly high bacterial diversity, with 150 operational taxonomic units belonging to 19 distinct taxonomic groups. Both samples were dominated by Zetaproteobacteria Fe oxidizers. This group was most abundant at Volcano 1, where sediments were richer in Fe and contained more crystalline forms of Fe oxides. Other groups of bacteria found at these two sites include known S‐ and a few N‐metabolizing bacteria, all ubiquitous in marine environments. The low similarity of our clones with the GenBank database suggests that new species and perhaps new families were recovered. The results of this study suggest that Fe‐rich hydrothermal sediments, while dominated by Fe oxidizers, can be exploited by a variety of autotrophic and heterotrophic micro‐organisms.     

Abundance and diversity of nitrogen-fixing bacteria in rhizosphere and bulk paddy soil under different duration of organic management

Denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR (qPCR) approaches were used to assess respectively the molecular diversity and quantity of the nifH gene sequences in rhizosphere and bulk paddy soil under conventional management and different duration of organic management (2, 3, 5, 9 years). The phylogenetic distribution of clones based on nifH gene sequence showed that taxonomic groups were consisted of Alphaproteobacteria (27.6%), Betaproteobacteria (24.1%) and Gammaproteobacteria (48.3%). Members of the order Rhizobiales and Pseudomonadales were prevalent among the dominant diazotrophs. When the quantity of the nifH gene sequences was determined by qPCR, 2.27 × 10⁵ to 1.14 × 10⁶ copies/g of soil were detected. Except for 2 years organically managed soil, nifH gene copy numbers in organic soil, both rhizosphere and bulk, were significantly higher than in CM soil. Moreover, nifH gene copy numbers in the organic rhizosphere soil (3, 5, 9 years) were significantly higher than in bulk soil. The abundance and diversity of nitrogen-fixing bacteria tended to increase with duration of organic management but the highest number of nifH gene copies was observed in the rhizosphere and bulk soil of 5 years organic management. In addition, analysis of variance and canonical correspondence analysis (CCA) showed that C/N, C and N were important factors influencing the abundance and community structure of nitrogen-fixing bacterial.     

Nutrient composition of Douglas-fir rhizosphere and bulk soil solutions

Rhizosphere soil solution is the direct source of nutrients for plant uptake. The nutrient composition of rhizosphere soil solution can be very different from that of bulk soil solution due to root exudation, nutrient uptake and rhizosphere microorganism activity. This study examined the nutrient composition of Douglas-fir rhizosphere soil solution in two soils belonging to the Nisqually and Pitcher soil series and compared rhizosphere solution with that of bulk soil solution. Fertilized and unfertilized Nisqually soils were also compared. Soil solutions were collected using centrifugation. Results indicated that nutrient concentrations in the rhizosphere solutions were typically higher than that of bulk soil solutions when no fertilizer was applied. Differences in the concentrations of nutrients between the rhizosphere and bulk soil solutions were masked by the addition of fertilizers. Rhizosphere solution pH also appeared to be affected by the concentration of NH₄ and NO₃ in the solution. With a higher concentration of NH₄ relative to NO₃ in the rhizosphere soil solution, the solution pH of the rhizosphere was lower than that of the bulk soil, but with a lower concentration of NH₄ relative to NO₃, the solution pH of the rhizosphere was higher than that of the bulk soil solution.     

小蓬竹根际土壤真菌多样性研究

为认识喀斯特山地适应竹种小蓬竹根际土壤微生物多样性,本文采用稀释平板法研究小蓬竹根际土壤真菌多样性。结果表明,菌落具有表型差异的真菌共33株,r DNA‐ITS进行BLAST划分为12个属24个种,相似度为75%–100%。子囊菌门真菌11个属、23个种、32株;担子菌门仅有1株,属多年卧孔菌属。子囊菌门的青霉属的菌株数量最多,占总菌株数21.21%。小蓬竹根际真菌数量为9.19×105/cfu?g,Shannon‐Wiener多样性指数H为2.2180,Margalef丰富度指数R为12,Pielou均匀度指数J为0.8926。     

健康与感染青枯病烟株根际土壤与茎秆细菌群落结构与多样性

【目的】了解健康烟株与感染青枯病烟株在根际土壤、茎杆发病部位、茎杆病健交界部位以及未发病茎杆的细菌群落结构与多样性。【方法】分别对土壤与茎杆样品中细菌的16S rRNA基因V3-V4区进行扩增,采用Illumina MiSeq测序技术对扩增片段进行高通量测序,然后对健康烟株与感染青枯病烟株不同部位细菌群落结构与多样性进行分析。【结果】感染青枯病烟株发病茎杆及根际土壤的细菌群落多样性高于健康烟株茎杆及其根际土壤样品,病健交界茎杆样品细菌群落多样性低于健康烟株。变形菌门(Proteobacteria)在所有样品中均为优势菌门;所有烟株根际土壤的优势菌门为拟杆菌门(Bacteroidetes)、酸杆菌门(Acidobacteria)、放线菌门(Actinobacteria)和绿弯菌门(Chloroflexi);健康烟株茎杆部位的优势菌门为蓝细菌门(Cyanobacteria);感染青枯病烟株发病茎杆和病健交界茎杆部位的优势菌门为蓝细菌门(Cyanobacteria)和厚壁菌门(Firmicutes)。所有根际土壤样品的优势菌属为劳尔氏菌属(Ralstonia)、假单胞菌属(Pseudomonas)、鞘脂单胞菌属(Sphingomonas)、黄杆菌属(Flavobacterium)和代尔夫特菌属(Delftia),而感染青枯病烟株根际土壤的劳尔氏菌属(Ralstonia)和假单胞菌属(Pseudomonas)相对丰度显著高于健康烟株根际土壤,鞘脂单胞菌属相对丰度显著低于健康烟株根际土壤。烟株茎杆的优势菌属为劳尔氏菌属和假单胞菌属等。感染青枯病烟株病健交界茎杆中劳尔氏菌属、肠杆菌属(Enterobacter)和泛菌属(Pantoea)相对丰度显著低于健康烟株样品。【结论】健康与感染青枯病烟株茎杆样品细菌群落的丰富度和多样性明显低于相应的根际土壤样品。较健康烟株而言,感染青枯病烟株根际土壤和茎杆样品细菌群落丰富度和多样性均表现出不同程度地增加,且根际土壤细菌群落结构变化较茎杆样品明显,而病健交界茎杆样品细菌群落丰富度和多样性降低。烟草青枯病为典型土传病害,其病原茄科劳尔氏菌尽管能在烟株维管束中蔓延扩增,但主要还是分布于土壤中;它的存在似乎对土壤细菌群落的影响大于茎杆样品的。该研究结果提示对于青枯病的防治不能局限于烟株本身,田间土壤也应加大防治力度。     

石油污染盐碱土壤翅碱蓬根围的细菌多样性及耐盐石油烃降解菌筛选

为了更好地了解石油污染盐碱土壤翅碱蓬根围的细菌多样性,采用16S rRNA基因克隆文库方法对其进行分析,在此基础上采用富集培养方法从该生境中分离筛选耐盐石油烃降解菌.16S rRNA基因克隆文库分析结果表明,海杆菌属(Marinobacter)、食烷菌属(Alcanivorax)和假单胞菌属(Pseudomonas)是该生境中的优势菌.他们可能在石油污染盐碱土壤翅碱蓬植物修复过程中起重要作用.进一步采用富集培养方法,从该生境中分离得到8株耐盐石油烃降解菌,可以耐受6％-10％浓度的NaCl,石油烃降解率在32.3％-57.0％之间.经16S rRNA基因序列分析,8株菌隶属于戈登氏菌属(Gordonia)、无色杆菌属(Achromobacter)、迪茨菌属(Dietzia)、芽胞杆菌属(Bacillus)和假单胞菌属(Pseudomonas).他们可能参与石油污染盐碱土壤翅碱蓬植物修复过程中的石油烃降解.     

Bacterial quorum sensing and nitrogen cycling in rhizosphere soil

Plant photosynthate fuels carbon-limited microbial growth and activity, resulting in increased rhizosphere nitrogen (N) mineralization. Most soil organic nitrogen is macromolecular (chitin, protein, nucleotides); enzymatic depolymerization is likely rate limiting for plant nitrogen accumulation. Analyzing Avena (wild oat) planted in microcosms containing sieved field soil, we observed increased rhizosphere chitinase and protease-specific activities, bacterial cell densities, and dissolved organic nitrogen (DON) compared with bulk soil. Low-molecular-weight (MW) DON (<3000 Da) was undetectable in bulk soil but comprised 15% of rhizosphere DON. Extracellular enzyme production in many bacteria requires quorum sensing (QS), cell-density-dependent group behavior. Because proteobacteria are considered major rhizosphere colonizers, we assayed the proteobacterial QS signals N-acyl-homoserine lactones (AHLs), which were significantly increased in the rhizosphere. To investigate the linkage between soil signaling and nitrogen cycling, we characterized 533 bacterial isolates from Avena rhizosphere: 24% had chitinase or protease activity and AHL production; disruption of QS in seven of eight isolates disrupted enzyme activity. Many Alphaproteobacteria were newly found with QS-controlled extracellular enzyme activity. Enhanced specific activities of nitrogen-cycling enzymes accompanied by bacterial density-dependent behaviors in rhizosphere soil gives rise to the hypothesis that QS could be a control point in the complex process of rhizosphere nitrogen mineralization.     

Isotopic biosignatures in carbonate‐rich,cyanobacteria‐dominated microbial mats of the Cariboo Plateau,B.C.

Photosynthetic activity in carbonate‐rich benthic microbial mats located in saline, alkaline lakes on the Cariboo Plateau, B.C. resulted in pCO₂ below equilibrium and δ¹³C_DIC values up to +6.0‰ above predicted carbon dioxide (CO₂) equilibrium values, representing a biosignature of photosynthesis. Mat‐associated δ¹³C_carb values ranged from ~4 to 8‰ within any individual lake, with observations of both enrichments (up to 3.8‰) and depletions (up to 11.6‰) relative to the concurrent dissolved inorganic carbon (DIC). Seasonal and annual variations in δ¹³C values reflected the balance between photosynthetic ¹³C‐enrichment and heterotrophic inputs of ¹³C‐depleted DIC. Mat microelectrode profiles identified oxic zones where δ¹³C_carb was within 0.2‰ of surface DIC overlying anoxic zones associated with sulphate reduction where δ¹³C_carb was depleted by up to 5‰ relative to surface DIC reflecting inputs of ¹³C‐depleted DIC. δ¹³C values of sulphate reducing bacteria biomarker phospholipid fatty acids (PLFA) were depleted relative to the bulk organic matter by ~4‰, consistent with heterotrophic synthesis, while the majority of PLFA had larger offsets consistent with autotrophy. Mean δ¹³C_org values ranged from ?18.7 ± 0.1 to ?25.3 ± 1.0‰ with mean Δ¹³C_inorg‐org values ranging from 21.1 to 24.2‰, consistent with non‐CO₂‐limited photosynthesis, suggesting that Precambrian δ¹³C_org values of ~?26‰ do not necessitate higher atmospheric CO₂ concentrations. Rather, it is likely that the high DIC and carbonate content of these systems provide a non‐limiting carbon source allowing for expression of large photosynthetic offsets, in contrast to the smaller offsets observed in saline, organic‐rich and hot spring microbial mats.     

Plant diversity shapes microbe‐rhizosphere effects on P mobilisation from organic matter in soil

Plant species richness (PSR) increases nutrient uptake which depletes bioavailable nutrient pools in soil. No such relationship between plant uptake and availability in soil was found for phosphorus (P). We explored PSR effects on P mobilisation [phosphatase activity (PA)] in soil. PA increased with PSR. The positive PSR effect was not solely due to an increase in C_org concentrations because PSR remained significant if related to PA:C_org. An increase in PA per unit C_org increases the probability of the temporal and spatial match between substrate, enzyme and microorganism potentially serving as an adaption to competition. Carbon use efficiency of microorganisms (C_mic:C_org) increased with increasing PSR while enzyme exudation efficiency (PA:C_mic) remained constant. These findings suggest the need for efficient C rather than P cycling underlying the relationship between PSR and PA. Our results indicate that the coupling between C and P cycling in soil becomes tighter with increasing PSR.     

Bacterial diversity of Taxus rhizosphere: culture-independent and culture-dependent approaches

The regional variability of Taxus rhizosphere bacterial community composition and diversity was studied by comparative analysis of three large 16S rRNA gene clone libraries from the Taxus rhizosphere in different regions of China (subtropical and temperate regions). One hundred and forty-six clones were screened for three libraries. Phylogenetic analysis of 16S rRNA gene sequences demonstrated that the abundance of sequences affiliated with Gammaproteobacteria, Betaproteobacteria, and Actinobacteria was higher in the library from the T. xmedia rhizosphere of the temperate region compared with the subtropical Taxus mairei rhizosphere. On the other hand, Acidobacteria was more abundant in libraries from the subtropical Taxus mairei rhizosphere. Richness estimates and diversity indices of three libraries revealed major differences, indicating a higher richness in the Taxus rhizosphere bacterial communities of the subtropical region and considerable variability in the bacterial community composition within this region. By enrichment culture, a novel Actinobacteria strain DICP16 was isolated from the T. xmedia rhizosphere of the temperate region and was identified as Leifsonia shinshuensis sp. via 16S rRNA gene and gyrase B sequence analyses. DICP16 was able to remove the xylosyl group from 7-xylosyl-10-deacetylbaccatin III and 7-xylosyl-10-deacetylpaclitaxel, thereby making the xylosyltaxanes available as sources of 10-deacetylbaccatin III and the anticancer drug paclitaxel. Taken together, the present studies provide, for the first time, the knowledge of the biodiversity of microorganisms populating Taxus rhizospheres.     

RISA、DGGE和2D-PAGE技术对大豆根际土壤细菌多样性分析的比较

采用基于PCR扩增的核糖体间隔区分析(RISA)、变性梯度凝胶电泳(DGGE)和双向电泳(2D-PAGE)3种分子生态学技术对大豆根际土壤细菌多样性比对分析.结果表明:2D-PAGE技术得到的土壤细菌多样性(基因点)最丰富,其次为DGGE技术(基因片段),RISA技术(基因片段)最低.RISA技术得到的条带数最少,但结...