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1.

Plant growth-promoting rhizobacteria are bacteria that improve plant growth and reduce plant pathogen damages. In this study, 100 nodule bacteria were isolated from chickpea, screened for their plant growth-promoting (PGP) traits and then characterised by PCR-RFLP of 16 S rDNA. Results showed that most of the slow-growing isolates fixed nitrogen but those exhibiting fast-growth did not. Fourteen isolates solubilized inorganic phosphorus, 16 strains produced siderophores, and 17 strains produced indole acetic acid. Co-culture experiments identified three strains having an inhibitory effect against Fusarium oxysporum, the primary pathogenic fungus for chickpea in Tunisia. Rhizobia with PGP traits were assigned to Mesorhizobium ciceri, Mesorhizobium mediterraneum, Sinorhizobium meliloti and Agrobacterium tumefaciens. We noted that PGP activities were differentially distributed between M. ciceri and M. mediterraneum. The region of Mateur in northern Tunisia, with clay–silty soil, was the origin of 53% of PGP isolates. Interestingly, we found that S. meliloti and A. tumefaciens strains did not behave as parasitic nodule-bacteria but as PGP rhizobacteria useful for chickpea nutrition and health. In fact, S. meliloti strains could solubilize phosphorus, produce siderophore and auxin. The A. tumefaciens strains could perform the previous PGP traits and inhibit pathogen growth also. Finally, one candidate strain of M. ciceri (LL10)—selected for its highest symbiotic nitrogen fixation and phosphorus solubilization—was used for field experiment. The LL10 inoculation increased grain yield more than three-fold. These finding showed the potential role of rhizobia to be used as biofertilizers and biopesticides, representing low-cost and environment-friendly inputs for sustainable agriculture.

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2.

The present study aimed to demonstrate the potential of abiotic stress-tolerant Jeotgalicoccus huakuii NBRI 13E for plant growth promotion and salt stress amelioration. NBRI 13E was characterized for abiotic stress tolerance and plant growth-promoting (PGP) attributes under normal and salt stress conditions. Phylogenetic comparison of NBRI 13E was carried out with known species of the same genera based on 16S rRNA gene. Plant growth promotion and rhizosphere colonization studies were determined under greenhouse conditions using maize, tomato, and okra. Field experiment was also performed to assess the ability of NBRI 13E inoculation for improving growth and yield of maize crop in alkaline soil. NBRI 13E demonstrated abiotic stress tolerance and different PGP attributes under in vitro conditions. Phylogenetic and differential physiological analysis revealed considerable differences in NBRI 13E as compared with the reported species for Jeotgalicoccus genus. NBRI 13E colonizes in the rhizosphere of the tested crops, enhances plant growth, and ameliorates salt stress in a greenhouse experiment. Modulation in defense enzymes, chlorophyll, proline, and soluble sugar content in NBRI 13E-inoculated plants leads to mitigate the deleterious effect of salt stress. Furthermore, field evaluation of NBRI 13E inoculation using maize was carried out with recommended 50 and 100% chemical fertilizer controls, which resulted in significant enhancement of all vegetative parameters and total yield as compared to respective controls. Jeotgalicoccus huakuii NBRI 13E is reported for the first time for its ability to develop a bioinoculant formulation for stress amelioration and improved crop productivity.

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3.
Four strains of heterotrophic, fusiform caulobacters have been isolated from freshwater sources. A single prostheca extends from one pole of mature cells, and cells attach to various substrata by means of a holdfast located at the distal tip of the appendage. Thus, superficially these bacteria bear a strong resemblance to bacteria in the genus Caulobacter. However, unlike Caulobacter these bacteria do not exhibit a dimorphic life cycle of motile, non-stalked daughter cells and immotile, stalked mother cells. Instead both mother and daughter cells are immotile, and at the time of cell separation the daughter cells are essentially identical mirror-image replicas of the mother cell. In addition, the prosthecae of these fusiform caulobacters do not have crossbands, they are somewhat wider than the stalks of Caulobacter and the pseudostalks of Asticcacaulis, and they terminate in a bulbous tip. The deoxyribonucleic acid (DNA) base composition ranges from 54.6–60.1, well below the 62–67 range for the genus Caulobacter. Based upon these and other differences, a new genus and species, Prosthecobacter fusiformis, is proposed for the fusiform caulobacters.  相似文献   

4.
Salt-induced soil degradation is common in farmlands and limits the growth and development of numerous crop plants in the world. In this study, we isolated salt-tolerant bacteria from the rhizosphere of Tamarix chinensis, Suaeda salsa and Zoysia sinica, which are common wild plants grown on a saline–alkaline land, to test these bacteria's efficiency in alleviating salt stress in tomato plants. We screened out seven strains (TF1–7) that are efficient in reducing salt stress in tomato seedlings. The sequence data of 16S rRNA genes showed that these strains belong to Arthrobacter and Bacillus megaterium. All strains could hydrolyze casein and solubilize phosphate, and showed at least one plant growth promotion (PGP)-related gene, indicating their potential in promoting plant growth. The Arthrobacter strains TF1 and TF7 and the Bacillus megaterium strain TF2 and TF3 could produce indole acetic acid under salt stress, further demonstrating their PGP potential. Tomato seed germination, seedling length, vigor index, and plant fresh and dry weight were enhanced by inoculation of Arthrobacter and B. megaterium strains under salt stress. Our results demonstrated that salt-tolerant bacteria isolated from the rhizosphere of wild plants grown on saline–alkaline lands could be used for alleviating salt stress in crop plants.  相似文献   

5.
Indigenous strains isolated from rhizosphere may contain highly competent genotypes to enhance the plant growth and often perform better than the introduced isolates. The present study deals with the characterisation of plant growth-promoting (PGP) attributes and antagonistic activity of Azotobacter chroococcum AZO2 against Macrophomina phaseolina causing charcoal rot disease and their effect on the growth of sesame (Sesamum indicum L.). Eight strains of Azotobacter were isolated from sesame rhizosphere on nitrogen-free medium, which exhibited significant PGP parameters such as phosphate solubilisation, indole acetic acid and siderophore production. The strain A. chroococcum AZO2 (EU274299) was characterised by 16S rDNA gene sequencing. Amplification of 781 bp nif H gene confirms nitrogenase activity of all the strains. A. chroococcum AZO2 exhibited strong antagonistic activities against M. phaseolina causing 81% colony growth inhibition and resulted in hyphal perforations, empty cell (halo) formation, hyphal twisting, shrinking and lysis of fungal mycelia along with degeneration of sclerotia. A. chroococcum AZO2 produced chitinase that caused degradation and digestion of the cell wall component of M. phaseolina. Different vegetative and reproductive parameters of sesame were found to be enhanced significantly upon application of A. chroococcum AZO2 + half doses of chemical fertilisers. A. chroococcum AZO2 was also found to be an effective root coloniser, plant growth promoter and potential antagonistic bacterium. It can be concluded that A. chroococcum AZO2 strain bears the characteristics of technological applications for inoculant preparation and growth enhancement of sesame besides being utilised as a better PGP bacterium as well as an effective agent for biocontrol of M. phaseolina.  相似文献   

6.
海洋固氮细菌在自然界氮循环中发挥着重要作用,筛选和开发海洋固氮促生的菌种资源,对于生物菌肥的开发应用和农业生产具有重要意义。[目的]研究海洋固氮细菌的生物多样性及对陆地作物的促生作用,筛选优良的植物根际促生菌株。[方法]通过形态特征、生理生化试验和16S rRNA基因序列比对进行菌属鉴定;将解磷、解钾、产蛋白酶和纤维素酶等性能优良的菌株作为菜心盆栽试验的组合菌液,探究对菜心能否起促生作用。[结果]本研究从南海东海岛的海岛沉积物中筛选出18株固氮菌,分布在6个属9种,不动杆菌属4株,假交替单胞菌属1株,芽孢杆菌属8株,嗜冷杆菌属1株,海单胞菌属1株,交替单胞菌属3株。菜心幼苗经过组合菌剂的浇灌,在茎高、茎粗、最大叶宽和最大叶长4个指标均表明对菜心有显著的促生作用。其中,以芽孢杆菌属和不动杆菌属的菌株在菜心的生长过程中起关键的促进作用,对菜心的促生性能最佳。[结论]南海近海具有种类丰富多样的固氮细菌,以芽孢杆菌属和不动杆菌属的菌株促生作用最为显著,具有开发成微生物菌肥的潜力,为优良的海洋促生微生物菌种资源的定向利用及蔬菜的无公害生产提供重要依据。  相似文献   

7.
【背景】随着工业化的发展,重金属污染逐渐成为主要的环境污染之一。微生物修复去除重金属污染成为近些年来新兴的修复方法,筛选开发具有良好修复功能的微生物菌株具有重要的现实意义。【目的】筛选具有促进植物生长作用的重金属修复菌株,为生物修复和植物促生等综合开发利用提供微生物资源。【方法】利用选择性培养基从淤泥中筛选重金属铅的抗性菌株,根据形态学观察、生理生化鉴定和16S rRNA基因序列分析对菌株进行分离鉴定,通过单因素分析不同培养条件对菌株生长的影响;采用原子吸收光谱法、比色法及平板对峙法等对菌株的重金属铅吸附率、无机磷溶解能力、吲哚乙酸(indole-3-acetic acid,IAA)分泌及拮抗镰刀菌效果等进行分析。【结果】从污染严重的塘泥中筛选到一株对重金属铅有较好吸附率的菌株,在150 mg/L Pb2+浓度下,对Pb2+的吸附率达90%以上;初步鉴定该菌株为蜡样芽孢杆菌,命名为SEM-15;菌株还具有较好的溶解无机磷、分泌IAA及拮抗镰刀菌的能力;菌株生长适应性强,可以在pH 10.0的强碱性环境下生长,该菌株具有很好的重金属铅污染修复及促生防病的应用潜力。【结论】菌株SEM-15是一株具有植物促生作用的重金属铅吸附菌株,在重金属污染土壤联合植物修复的应用中可能具有较好的开发价值。  相似文献   

8.
Key message

Combining with a CRISPR/Cas9 system, Agrobacterium-mediated transformation can lead to precise targeted T-DNA integration in the rice genome.

Abstract

Agrobacterium-mediated T-DNA integration into the plant genomes is random, which often causes variable transgene expression and insertional mutagenesis. Because T-DNA preferentially integrates into double-strand DNA breaks, we adapted a CRISPR/Cas9 system to demonstrate that targeted T-DNA integration can be achieved in the rice genome. Using a standard Agrobacterium binary vector, we constructed a T-DNA that contains a CRISPR/Cas9 system using SpCas9 and a gRNA targeting the exon of the rice AP2 domain-containing protein gene Os01g04020. The T-DNA also carried a red fluorescent protein and a hygromycin resistance (hptII) gene. One version of the vector had hptII expression driven by an OsAct2 promoter. In an effort to detect targeted T-DNA insertion events, we built another T-DNA with a promoterless hptII gene adjacent to the T-DNA right border such that integration of T-DNA into the targeted exon sequence in-frame with the hptII gene would allow hptII expression. Our results showed that these constructs could produce targeted T-DNA insertions with frequencies ranging between 4 and 5.3% of transgenic callus events, in addition to generating a high frequency (50?80%) of targeted indel mutations. Sequencing analyses showed that four out of five sequenced T-DNA/gDNA junctions carry a single copy of full-length T-DNA at the target site. Our results indicate that Agrobacterium-mediated transformation combined with a CRISPR/Cas9 system can efficiently generate targeted T-DNA insertions.

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9.
Abstract

The Agrobacterium-mediated ability to transfer genes into organisms without sexual crossing provides breeders with new opportunities to improve the efficiency of plant production. Gene transfer offers advantages over classical genetic manipulation since plants are improved without disruption of the integrity of their genomes. Several useful genes isolated from microrganisms and affecting pest resistance, rooting ability, hormonal metabolism etc., are now available. These genes can be easily cloned into suitable Ti and Ri derived plasmid vectors and transferred into woody species. The scarce ability of most fruit trees to regenerate the whole plant from in vitro-cultured cells remains the main obstacle to a wider use of gene transfer technology.  相似文献   

10.
Aims: Aim of this study is to determine the genetic variation of rhizobia associated with horse gram [Macrotyloma uniflorum (Lam.) Verdc.] plants grown in different regions of Andhra Pradesh, India. Methods and Results: Four representative isolates having most representative characters from the previous characterization were selected for 16S rRNA sequence. The sequences were submitted to the NCBI GenBank and Ribosomal Database Project (RDP). The isolates HGR‐4, 6 and 13 showed more than 99% homology between them and they were grouped with Rhizobium reference strains where as the isolate HGR‐25 showed 87·1, 87·4 and 87·2% homology with the isolates HGR‐4, 6 and 13, respectively, and were grouped with reference strains for Caulobacter. The nodulation ability of these isolates on horse gram was confirmed by inoculation tests. Conclusions: The isolate HGR‐25 was identified as Caulobacter isolated from the plants growing in soil samples collected from Khareemnagar district, Andhra Pradesh, India. Inoculation tests revealed that Caulobacter formed nodules on horse gram. It was also confirmed by RDP. Significance and Impact of the Study: This is the first report that a legume was nodulated by a member of the genus Caulobacter, which belongs to the family Caulobacteriaceae in the order Caulobacterales of Alphaproteobacteria.  相似文献   

11.
The presence of explosives in soils and the interaction with drought stress and nutrient limitation are among the environmental factors that severely affect plant growth on military soils. In this study, we seek to isolate and identify the cultivable bacteria of a 2,4‐dinitrotoluene (DNT) contaminated soil (DS) and an adjacent grassland soil (GS) of a military training area aiming to isolate new plant growth‐promoting (PGP) and 2,4‐DNT‐degrading strains. Metabolic profiling revealed disturbances in Ecocarbon use in the bare DS; isolation of cultivable strains revealed a lower colony‐forming‐unit count and a less diverse community associated with DS in comparison with GS. New 2,4‐DNT‐tolerant strains were identified by selective enrichments, which were further characterized by auxanography for 2,4‐DNT use, resistance to drought stress, cold, nutrient starvation and PGP features. By selecting multiple beneficial PGP and abiotic stress‐resistant strains, efficient 2,4‐DNT‐degrading consortia were composed. After inoculation, consortium UHasselt Sofie 3 with seven members belonging to Burkholderia, Variovorax, Bacillus, Pseudomonas and Ralstonia species was capable to successfully enhance root length of Arabidopsis under 2,4‐DNT stress. After 9 days, doubling of main root length was observed. Our results indicate that beneficial bacteria inhabiting a disturbed environment have the potential to improve plant growth and alleviate 2,4‐DNT stress.  相似文献   

12.
Eight bacterial isolates from the larval guts of Diamondback moths (Plutella xylostella) were tested for their plant growth–promoting (PGP) traits and effects on early plant growth. All of the strains tested positive for nitrogen fixation and indole 3-acetic acid (IAA) and salicylic acid production but negative for hydrogen cyanide and pectinase production. In addition, five of the isolates exhibited significant levels of tricalcium phosphate and zinc oxide solubilization; six isolates were able to oxidize sulfur in growth media; and four isolates tested positive for chitinase and β-1,3-glucanase activities. Based on their IAA production, six strains including four that were 1-aminocyclopropane-1-carboxylate (ACC) deaminase positive and two that were ACC deaminase negative were tested for PGP activity on the early growth of canola and tomato seeds under gnotobiotic conditions. Acinetobacter sp. PSGB04 significantly increased root length (41%), seedling vigor, and dry biomass (30%) of the canola test plants, whereas Pseudomonas sp. PRGB06 inhibited the mycelial growth of Botrytis cinerea, Colletotrichum coccodes, C. gleospoiroides, Rhizoctonia solani, and Sclerotia sclerotiorum under in vitro conditions. A significant increase, greater than that of the control, was also noted for growth parameters of the tomato test plants when the seeds were treated with PRGB06. Therefore, the results of the present study suggest that bacteria associated with insect larval guts possess PGP traits and positively influence plant growth. Therefore, insect gut bacteria as effective PGP agents represent an unexplored niche and may broaden the spectrum of beneficial bacteria available for crop production.  相似文献   

13.
缓解花生连作障碍的根际促生菌分离及功能鉴定   总被引:1,自引:0,他引:1  
【目的】长期连作障碍严重降低花生生产的产量及品质,根际促生菌可有效降解土壤中自毒化感物质、抑制植物病原菌生长及促进植物生长,从而有效缓解连作障碍问题。筛选优化具有缓解花生连作障碍能力的多功能根际益生微生物,验证其益生作用能力,为根际促生菌株在连作障碍中的应用提供理论依据及技术支持。【方法】采集连作12年地块花生根际土壤,利用以酚酸为唯一碳源的筛选培养基获得具有酚酸自毒化感物质降解及利用能力的根际促生菌,通过16S rRNA基因测序进行系统发育分析,确定根际促生菌菌株的分类地位,并验证其对植物病原菌生长抑制能力及解磷、解钾、产植物激素吲哚乙酸能力。【结果】从连作12年的花生发病土壤中获得7株可高效降解酚酸类自毒物质且降解底物多样的根际微生物菌株,经16S rRNA测序比对分别为克雷伯氏菌B02 (Klebsiella sp. B02)、克雷伯氏菌B07(Klebsiella sp. B07)、克雷伯氏菌B15 (Klebsiella sp. B15)、芽孢杆菌B28 (Bacillus sp. B28)、不动杆菌P09(Acinetobacter sp. P09)、布鲁氏杆菌VA05 (...  相似文献   

14.
Background

Genomic islands (GIs) are clusters of alien genes in some bacterial genomes, but not be seen in the genomes of other strains within the same genus. The detection of GIs is extremely important to the medical and environmental communities. Despite the discovery of the GI associated features, accurate detection of GIs is still far from satisfactory.

Results

In this paper, we combined multiple GI-associated features, and applied and compared various machine learning approaches to evaluate the classification accuracy of GIs datasets on three genera: Salmonella, Staphylococcus, Streptococcus, and their mixed dataset of all three genera. The experimental results have shown that, in general, the decision tree approach outperformed better than other machine learning methods according to five performance evaluation metrics. Using J48 decision trees as base classifiers, we further applied four ensemble algorithms, including adaBoost, bagging, multiboost and random forest, on the same datasets. We found that, overall, these ensemble classifiers could improve classification accuracy.

Conclusions

We conclude that decision trees based ensemble algorithms could accurately classify GIs and non-GIs, and recommend the use of these methods for the future GI data analysis. The software package for detecting GIs can be accessed at http://www.esu.edu/cpsc/che_lab/software/GIDetector/.

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15.
Background

The apoplast plays an important role in plant defense against pathogens. Some extracellular PR-4 proteins possess ribonuclease activity and may directly inhibit the growth of pathogenic fungi. It is likely that extracellular RNases can also protect plants against some viruses with RNA genomes. However, many plant RNases are multifunctional and the direct link between their ribonucleolytic activity and antiviral defense still needs to be clarified. In this study, we evaluated the resistance of Nicotiana tabacum plants expressing a non-plant single-strand-specific extracellular RNase against Cucumber mosaic virus.

Results

Severe mosaic symptoms and shrinkage were observed in the control non-transgenic plants 10 days after inoculation with Cucumber mosaic virus (CMV), whereas such disease symptoms were suppressed in the transgenic plants expressing the RNase gene. In a Western blot analysis, viral proliferation was observed in the uninoculated upper leaves of control plants, whereas virus levels were very low in those of transgenic plants. These results suggest that resistance against CMV was increased by the expression of the heterologous RNase gene.

Conclusion

We have previously shown that tobacco plants expressing heterologous RNases are characterized by high resistance to Tobacco mosaic virus. In this study, we demonstrated that elevated levels of extracellular RNase activity resulted in increased resistance to a virus with a different genome organization and life cycle. Thus, we conclude that the pathogen-induced expression of plant apoplastic RNases may increase non-specific resistance against viruses with RNA genomes.

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16.
烟草根际可培养微生物多样性及防病促生菌的筛选   总被引:1,自引:0,他引:1  
【背景】根际微生物在植物根部生态系统中扮演着重要角色,影响着植物的营养吸收和健康生长。【目的】了解常年不发病烟田烤烟品种K326根际可培养微生物的多样性,筛选具有防病促生功能的菌株,为烟草病害绿色防控提供资源。【方法】采用传统培养方法对烟草根际土壤中的细菌和真菌进行分离鉴定,评价菌株的促生特性及病原菌拮抗能力,并进一步验证典型菌株对盆栽烟苗的促生效果。【结果】共获得261株微生物菌株,包括160株细菌和101株真菌。经分子鉴定,细菌中以变形菌门(Proteobacteria)和厚壁菌门(Firmicutes)为主要类群;真菌中以子囊菌门(Ascomycota)和毛霉菌门(Mucoromycota)为主要类群。在属水平上,细菌以假单胞菌属(Pseudomonas)和芽孢杆菌属(Bacillus)为主,真菌以曲霉属(Aspergillus)和青霉属(Penicillium)为主。从不同种水平上进一步选择44株细菌为代表菌株,发现它们均具有不同程度的吲哚-3-乙酸(Indole-3-Acetic Acid,IAA)产生能力,9株能够溶解有机磷,16株能够溶解无机磷,13株产生铁载体,14株产...  相似文献   

17.
It has been clearly established that phytopathogenic fungi, bacteria, and viruses exert biotic stresses on plants. Much less is known, however, about the interactions between enological species of yeast and their host plants. In a previous study, we described how Saccharomyces cerevisiae, the most common enological yeast, can act as a grapevine (Vitis vinifera L.) pathogen, causing growth retardation or plant death. In the present in vitro study on 11 strains of yeast belonging to different genera, which often occur on the surfaces of vineyard grapes and V. vinifera, a link was found to exist between strain phytopathogenecity and pseudohyphal growth habits and/or endopolygalacturonase activity. The results obtained here are consistent with earlier findings showing that the phytopathogenicity of yeast strains depends on the filamentous growth process, and show that endopolygalacturonase alone is not responsible for the invasion of plants tissues. The mechanisms observed here may be of significant ecological importance and may help to explain the long periods of yeast survival found to occur in vineyards.  相似文献   

18.
Symbiotic endophytes, unlike plant pathogens, do not usually induce visible host response. This may constraint the researcher's decision whether a plant has been successfully infected by the endophyte. In order to properly study the establishment, development and progress of an endophyte in the host plant and host-endophyte interactions, methods for the identification and localization of endophytic microorganisms are needed. Towards this aim, we focused at two levels: (A) We constructed M. albus-specific primers for polymerase chain reaction (PCR). In vitro, these primers specifically detected only M. albus strains and not isolates of related fungi (such as Daldinia sp. and a Xylariaceae sp.). (B) For direct visualization of the fungi, we inserted a reporter gene (gfp) into M. albus hyphae using Agrobacterium-mediated transformation. Since M. albus is a sterile fungus (i.e., without spores or fungal fruiting bodies), we used chopped fungal mycelium for the transformation procedure. We transformed three different isolates of M. albus using Agrobacterium-mediated transformation. Fifty-nine different transformants were collected with a transformation efficacy of 0.0004–0.0026%. Although PCR-based detection and direct visualization of the transformants in planta were unsuccessful, all tested transformants (with one exception) exhibited similar biological activity to their cognate wild type. This work provides a significant step forward in molecular research of the relationships between this endophytic genus and their hosts.  相似文献   

19.
Achieving specific counting of plant growth promoting (PGP) microorganisms maintained at high numbers in inert carriers such as peat is an important objective for the inoculation of field crops such as cereals. In this paper, methods based on selective media together with strain-specific counting using enzyme-linked immunoassay (ELISA) were examined. Selective plate counting was developed by screening four commercial PGP biofertiliser strains for resistance to antibiotics. ELISAs for each strain were developed and calibrated by purifying polyclonal antibodies, testing sample pre-treatment strategies, and investigating the effect of culture age on standard curves. Selective plate counting proved to be more accurate than the ELISA methodology, confirming that all microbial strains survived for at least 1 month in sterile peat without loss in viable numbers, and further demonstrated growth inhibition of the strain Candida tropicalis HY when co-inoculated with the other strains Pseudomonas fluorescens 1 N, Bacillus amyloliquefaciens E19 and Bacillus subtilis B9. This is the first known study to have investigated the dynamics of PGP microorganisms in multi-strain inoculants and demonstrates the utility and hitherto unmentioned drawbacks of two different low-cost counting methods for biofertiliser quality control. Such information is vital for the adoption and success of non-rhizobial PGP biofertilisers for sustainable agriculture.  相似文献   

20.
Based on 16S rRNA gene analyses, the same bacterial operational taxonomic units (OTUs) are common to both the Arctic and Antarctic oceans, supporting the concept ‘everything is everywhere’. However, whether the same OTUs from both poles have identical genomes, i.e. whether ‘everything is still everywhere’ at the genomic level has not yet been examined systematically. Here, we isolated, sequenced and compared the genomes of 45 culturable marine bacteria belonging to three genera of Salinibacterium, Psychrobacter and Pseudoalteromonas from both polar oceans. The bacterial strains with identical 16S rRNA genes were common to both poles in every genus, and four identical genomes were detected in the genus Salinibacterium from the Arctic region. However, no identical genomes were observed from opposite poles in this study. Our data, therefore, suggest that ‘everything is not everywhere’ at the genomic level. The divergence time between bacteria is hypothesized to exert a strong impact on the bacterial biogeography at the genomic level. The geographical isolation between poles was observed for recently diverged, highly similar genomes, but not for moderately similar genomes. This study thus improves our understanding of the factors affecting the genomic-level biogeography of marine microorganisms isolated from distant locations.  相似文献   

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