Rhizosphere Soil Of Plants Research Articles

Arbuscular Mycorrhizal Fungal Assemblages Significantly Shifted upon Bacterial Inoculation in Non-Contaminated and Petroleum-Contaminated Environments.

Arbuscular mycorrhizal fungi (AMF) have been shown to reduce plant stress and improve their health and growth, making them important components of the plant-root associated microbiome, especially in stressful conditions such as petroleum hydrocarbons (PHs) contaminated environments. Purposely manipulating the root-associated AMF assemblages in order to improve plant health and modulate their interaction with the rhizosphere microbes could lead to increased agricultural crop yields and phytoremediation performance by the host plant and its root-associated microbiota. In this study, we tested whether repeated inoculations with a Proteobacteria consortium influenced plant productivity and the AMF assemblages associated with the root and rhizosphere of four plant species growing either in non-contaminated natural soil or in sediments contaminated with petroleum hydrocarbons. A mesocosm experiment was performed in a randomized complete block design in four blocks with two factors: (1) substrate contamination (contaminated or not contaminated), and (2) inoculation (or not) with a bacterial consortium composed of ten isolates of Proteobacteria. Plants were grown in a greenhouse over four months, after which the effect of treatments on plant biomass and petroleum hydrocarbon concentrations in the substrate were determined. MiSeq amplicon sequencing, targeting the 18S rRNA gene, was used to assess AMF community structures in the roots and rhizosphere of plants growing in both contaminated and non-contaminated substrates. We also investigated the contribution of plant identity and biotope (plant roots and rhizospheric soil) in shaping the associated AMF assemblages. Our results showed that while inoculation caused a significant shift in AMF communities, the substrate contamination had a much stronger influence on their structure, followed by the biotope and plant identity to a lesser extent. Moreover, inoculation significantly increased plant biomass production and was associated with a decreased petroleum hydrocarbons dissipation in the contaminated soil. The outcome of this study provides knowledge on the factors influencing the diversity and community structure of AMF associated with indigenous plants following repeated inoculation of a bacterial consortium. It highlights the dominance of soil chemical properties, such as petroleum hydrocarbon presence, over biotic factors and inputs, such as plant species and microbial inoculations, in determining the plant-associated arbuscular mycorrhizal fungi communities.

Comparison of the Rhizosphere Soil Microbial Community Structure and Diversity Between Powdery Mildew-Infected and Noninfected Strawberry Plants in a Greenhouse by High-Throughput Sequencing Technology

The aim of this study was to compare the microbial community structure and diversity in powdery mildew-infected and noninfected strawberry plant rhizosphere soils in the greenhouse based on variations in the 16S rRNA gene V3-V4 and fungal ITS2 regions by Illumina amplicon sequencing. Powdery mildew infection reduced the number of operational taxonomic units (OTUs) and prokaryotic and fungal community richness/diversity indexes in the rhizosphere soils compared with those in healthy plant soils. Furthermore, 3543 prokaryotic and 581 fungal OTUs were obtained at the 97% similarity level. Proteobacteria, Actinobacteria, Bacteroidetes, Acidobacteria, and Chloroflexi were the dominant bacterial phyla; Woesearchaeota_DHVEG-6, Bathyarchaeota, and Thaumarchaeota were the dominant archaea; and Ascomycota, Basidiomycota, unclassified_fungi, and Zygomycota were the dominant fungal phyla. Their proportions differed significantly among samples. Wolbachia, Devosia, Pseudolabrys, Streptomyces, and Rhizomicrobium were the most abundant bacterial genera; their proportions differed significantly among samples. Most Pseudomonas, Streptomyces, and 'norank' group members might be potential antagonistic microorganisms of powdery mildew pathogens, and Wolbachia and Rickettsia might be pathogen-transmitting vectors. Microascus, Clitopilus, and Ciliophora were the dominant fungi, and their community structures and abundances significantly differed among samples. Microascus, Talaromyces, Zopfiella, and Cryptococcus were relatively more abundant in the powdery mildew-infected strawberry plant rhizosphere soils. Fusarium, Trichoderma, Clitopilus, and 'unclassified' group members may be potential antagonistic populations. The results suggested that powdery mildew-infected strawberry fruits and plants cannot be consumed. This report is the first study to illustrate differences in the rhizosphere soil prokaryotic and fungal communities between powdery mildew-infected and noninfected strawberry plants in a greenhouse.

Comparison of bacterial communities in soil samples with and without tomato bacterial wilt caused by Ralstonia solanacearum species complex

BackgroundRalstonia solanacearum is one of the most notorious soil-borne phytopathogens. It causes a severe wilt disease with deadly effects on many economically important crops. The microbita of disease-suppressive soils are thought that they can contribute to the disease resistance of crop plants, thus, evaluation of the microbial community and their interaction characteristics between suppressive soil (SS) and conducive soil (CS) will help to understand resistance mechanism. To do this, the bacterial community structure, correlation analysis with soil chemical properties, interaction network of SS (nearly no disease in three years), and CS (suffered heavy bacterial wilt disease) were analyzed.ResultsA higher bacterial community diversity index was found in SS, the relative abundance of Nocardioides, Gaiella and norank_f_Anaerolineaceae were significantly more than that of the CS. Moreover, the relative abundance of main genera Bacillus, norank_o_Gaiellales, Roseiflexus, and norank_o_Gemmatimonadaceae were significantly more than that of the CS. Redundancy analysis at the genus level indicated that the available phosphate played a key role in the bacterial community distribution, and its role was negatively correlated with soil pH, organic matter content, alkali-hydrolyzable nitrogen, and available potassium contents. Interaction network analysis further demonstrated that greater diversity at the genus level existed in the SS network and formed a stable network. Additionally, the species of Mycobacterium, Cyanobacteria, and Rhodobiaceae are the key components that sustain the network stability. Seven clusters of orthologous groups exhibited significant differences between SS and CS. Moreover, 55 bacterial strains with distinct antagonistic activities to R. solancearum were isolated and identified from the healthy tomato plant rhizosphere soil of the CS.ConclusionsOur findings indicate that the bacterial diversity and interaction network differed between the CS and SS samples, providing a good foundation in the study of bacterial wilt.

Effects of Soil Microbiomes and Enzymatic Activities on Glechoma longituba

Soil microbes and enzymes play important roles in plant growth and metabolism. However, for Glechoma longituba (Nakai) Kupr., an important crop with edible and medicinal uses in China, their effects are not well elucidated. To explore their impacts on plant morphology and bioactive compounds, the plant samples and rhizosphere soil of five different G. longituba populations were collected and investigated in this study. After high-throughput sequencing combined with data analyses, high microbial diversity and richness in the rhizosphere soil of each G. longituba population were observed, and the variations on bacterial and fungal community compositions among these soil samples were also proved. The activities of urease, neutral phosphatase, sucrase, protease, and polyphenol oxidase were significantly different among the rhizosphere soils from different G. longituba populations. Among the major microbial communities and soil enzymes we studied, the genera of Tomentella, Sebacina, Fusarium, Nitrospira, and the activity of soil sucrase were remarkably correlative with both the morphological indices and the contents of bioactive compounds of G. longituba by redundancy analysis. These findings would help guide the scientific plantation of G. longituba to promote its medicinal quality.

Rhizosphere bacteria are more strongly related to plant root traits than fungi in temperate montane forests: insights from closed and open forest patches along an elevational gradient

Heterogeneous canopies in temperate montane forests affect microclimate and soil characteristics, with important effects on soil microbial communities and related processes. Here, we studied the interactions between plant root traits and soil bacterial and fungal communities in closed forest and open gaps in a mixed forest along an elevational gradient in the French Alps (1400, 1700 and 2000 m). Samples were separated into three fractions (plant root, rhizosphere and bulk soil), to further investigate the influence of plant zones on microbial communities. Bacterial (16S) and fungal (ITS) biodiversity was determined using high throughput sequencing, along with standard measures of soil, litter and root traits. We found that (i) microbial community diversity was higher in gaps than in closed forest because of increased root trait diversity and density; (ii) open versus closed forest patches affected phylogenetic dispersion despite differences in elevations with phylogenetic clustering in closed forest; (iii) the interaction between root traits and microbial communities was stronger for rhizosphere and root fractions than for bulk soil and (iv) bacterial community composition was better explained by root traits than for fungi. Our findings highlight the importance of open gaps versus closed forest patches and associated root traits affecting microbial community structure, particularly for bacterial assemblages that exhibited a stronger interaction with root traits than for fungi.

Quantitative estimation of complex phosphate - solubilization by immobilized or free Azospirillum Lipoferum (H3) as vital vaccine in Pikovskaya broth (PVK) medium

Azospirillum species were collected from the rhizosphere and free soil of different plants in Al-Jabal El- Akhdar region. The isolates were identified according to biochemical activities. Isolate (H3) which showed the higher solubilization efficiency (SE) on Pikovskaya medium (PVK) containing insoluble phosphate (inorganic phosphate) Ca3(po4)2 Isolate (H3) was identified as Azospirillum lipoferum (H3), which used as an inoculum as free cell suspension or as alginate formulation. Phosphate solubilization was measured by A.lipoferum (H3) as free or alginate immobilized cells in (PVK) liquid medium and recording the pH of the medium at the same time. The results showed in the phosphorus content by immobilized bacteria in liquid (PVK) broth medium from 2nd day of incubation (2.48 µg/ ml) to 10th day (3.70 µg/ ml) and the free bacteria from 2nd day (8.81 µg/ ml) to 10th day (4.49 µg/ ml). pH of the liquid (PVK) broth medium was recorded from 2nd day to 10th day after incubation which decreased by immobilized A.lipoferum (H3) from 7.00 pH to 4.47 on the 10th day and by the free A.lipoferum (H3) to 6.00, which improved the production of organic acids from sugars which was response of decreasing the pH of the medium. This present study contribute to make agriculture more productive with less harm to the environment and for developing countries where the use of fertilizers is costly, and to encourage of using the biofertilizers ‘plant growth promoting rhizobacteria’ (PGPR) instead of the chemical fertilizers to enhance the plant growth which is the main goal to increase the food production in a healthy way.

Effect of soil pH and organic matter content on heavy metals availability in maize (Zea mays L.) rhizospheric soil of non-ferrous metals smelting area.

Maize plant tissues and rhizosphere soil were collected from an agricultural area around the Huludao Zinc Plant in Liaoning Province, China, to investigate the effects of soil pH and organic matter content on heavy metal concentration and accumulation in different types of maize tissues. The mean pH of the soil samples was 7.02 (range 5.74-7.86), and the mean organic matter content was 31.03gkg-1 (range 18.80-52.20gkg-1). The average Cu, Zn, Pb, and Cd contents in soil were 2.92, 6.72, 7.95, and 16.28 times greater than the corresponding background values, respectively. The geo-accumulation index indicated that the soils were uncontaminated to moderately contaminated by Cu, moderately to strongly contaminated by Pb and Zn, and strongly contaminated by Cd. The average available Cu, Pb, Zn, and Cd contents in the soil samples were 16.34, 6.997, 69.77, and 0.190mgkg-1, respectively, while their bioavailability coefficients were 28.53%, 1.65%, 40.44%, and 10.83%, respectively. The respective mean Pb and Cd concentrations in grain samples were 0.341 and 0.342mgkg-1, which exceeded the maximum concentrations permitted by the Chinese National Standard. Thus, the maize grain is not safe for consumption and poses potential risks to human health. With the exception of Cu, the combined effect of pH and organic matter content had a stronger influence on the availability of heavy metals in soil compared with either factor alone. Cd uptake in maize plant tissues was affected by the combination of soil pH, organic matter content, and bioavailable Cd content in soil; however, the combination of these three factors had only slight effects on Cu, Zn, and Pb absorption in maize tissues.

GC-MS analysis of yellow pigmented Macrococcus equipercicus isolated from alfalfa rhizosphere soil fields of Coimbatore

The rhizosphere of plant possesses important microflora, which secretes wide chemical compounds including secondary metabolites necessary for plant growth and development. The microbial flora of alfalfa plant rhizosphere soil region was explored for functional activity and we found upto ten different pigmented colonies. Due to good functional diversity, this yellow pigmented colony was taken for further studies. Thus, the culture was molecularly characterized and identified for potent bioactive components responsible for antimicrobial activity. The selected culture mass was cultured and secondary metabolites were produced and extracted using ethyl acetate and subjected to GC-MS analysis. The antimicrobial study revealed selective activity against Streptococcus pneumonia, and Proteus sp with zone of inhibition to be 18 and 20 mm respectively. Molecular identification of the isolate by 16S rRNA sequencing showed the isolate as Macrococcus equipercicus with 100 % similarity. Based on GC-MS analysis report 25bioactive compounds were identified and 13-docosenamide, hexadecanoic acid esters and quercetin were found in ethyl acetate extract. Conclusion: Thus the yellow pigmented gram positive cocci M.equipercicus isolated from Medicago sativa possessed wide antibacterial activity due to presence of quercetin. Through the studies, we were able to identify potent antibacterial compound producing bacteria from M. sativa plant rhizosphere soil.

Effects of Two Trichoderma Strains on Plant Growth, Rhizosphere Soil Nutrients, and Fungal Community of Pinus sylvestris var. mongolica Annual Seedlings

Trichoderma spp. are proposed as major plant growth-promoting fungi that widely exist in the natural environment. These strains have the abilities of rapid growth and reproduction and efficient transformation of soil nutrients. Moreover, they can change the plant rhizosphere soil environment and promote plant growth. Pinus sylvestris var. mongolica has the characteristics of strong drought resistance and fast growth and plays an important role in ecological construction and environmental restoration. The effects on the growth of annual seedlings, root structure, rhizosphere soil nutrients, enzyme activity, and fungal community structure of P. sylvestris var. mongolica were studied after inoculation with Trichoderma harzianum E15 and Trichoderma virens ZT05, separately. The results showed that after inoculation with T. harzianum E15 and T. virens ZT05, seedling biomass, root structure index, soil nutrients, and soil enzyme activity were significantly increased compared with the control (p < 0.05). There were significant differences in the effects of T. harzianum E15 and T. virens ZT05 inoculation on the growth and rhizosphere soil nutrient of P. sylvestris var. mongolica (p < 0.05). For the E15 treatment, the seedling height, ground diameter, and total biomass of seedlings were higher than that those of the ZT05 treatment, and the rhizosphere soil nutrient content and enzyme activity of the ZT05 treatment were higher than that of the E15 treatment. The results of alpha and beta diversity analyses showed that the fungi community structure of rhizosphere soil was significantly different (p < 0.05) among the three treatments (inoculated with T. harzianum E15, T. virens ZT05, and not inoculated with Trichoderma). Overall, Trichoderma inoculation was correlated with the change of rhizosphere soil nutrient content.

Rhizosphere provides a new paradigm on the prevalence of lysogeny in the environment

Bacteria and phage enter into lysogeny to survive under nutrient-limiting environment. Plant-soil feedback improves nutrients and increases density and diversity of bacteria in the rhizosphere soil, however, its impact on lysogeny is not understood. The rhizosphere and bulk soil of plants colonizing nutrient-deficient abandoned mines may serve as ideal habitats to analyze the role of plants in governing lifestyle of bacteria and phage. Therefore, to unravel the importance of rhizosphere as a determinant of lysogeny, we analyzed bulk and rhizosphere soils of wild grass, Saccharum munja from an abandoned mine in Delhi (India) for nutrient concentration, bacterial density and diversity, and lysogens. We hypothesized that the rhizosphere, though nutrient-rich, remains nutrient-limiting and favours lysogeny because of an intense competition among bacteria for nutrients. Soil analyses confirmed that Bhatti mine soil was sandy loam with low concentration of nutrients but wild grass exerts a strong rhizosphere effect on the mine soil and improves its nutrient concentration and bacterial density and diversity. The rhizosphere soil, though nutrient-rich, supports 94–100% Mitomycin C-induced lysogens, whereas, the bulk soil, though nutrient-limiting, harbors 70–71% of Mitomycin C-induced lysogens only. The 16S rRNA sequencing showed a similar trend of bacterial diversity as bulk soil harbours bacteria of 2 genera and 3 species, whereas rhizosphere soil supports bacteria of 8 genera, 25 species. The rhizosphere soil showed 170 times higher colony-forming units than the bulk soil. Lysogeny in the rhizosphere is a characteristic of the highly competitive environment of the species-rich bacterial community. We emphasize that the gross concentration of nutrients alone provides a limited view of nutrient scarcity because high density and diversity rhizobacteria create a challenge of access to nutrients and thus present a nutrient-limiting environment. The rhizosphere, therefore, provides a new paradigm to explain lysogeny in soil. A factorial design experiment involving varying nutrients and bacterial competition would further help in unraveling the ecological significance of lysogeny in soils.

Effects of arbuscular mycorrhizal fungi on inoculated seedling growth and rhizosphere soil aggregates

Arbuscular mycorrhizal fungi (AMF) inoculation have been shown to enhance host plant growth and rhizosphere soil aggregates largely due to the combined effect of extraradical hyphae and glomalin-related soil proteins but their effects on rocky desertified soils remain unknown. Extensive karst area of southwest China has undergone rocky desertification because of soil erosion and vegetation degradation. Karst soils in this area are mainly composed of silty clay loam developed from carbonate rock erosion under subtropical humid monsoon climate. We tested the hypothesis that AMF colonization of tree seedlings would improve water stable aggregates of degraded karst soil and enhance seedling growth. Seedlings of two tree species, Toona sinensis and Delavaya toxocarpa suitable for afforestation in karst area, were inoculated separately with three AMF, Funneliformis mosseae, Glomus versiforme and Rhizophagus intraradices in pots containing rocky desertified soil. Non-inoculated seedlings were used as control. After 12 months we found that the percentage of water stable aggregates (diameter >0.25 mm; WSA>0.25) in the rhizosphere soil of the inoculated seedlings was increased by 15.6–20.5% compared to control. AMF colonization significantly increased the quantity of aggregates with diameter > 2 mm compared to control but soil aggregates of size class 0.25 – 0.5 mm decreased significantly in inoculated seedlings, regardless of tree species. Shoot biomass of inoculated T. sinensis and D. toxocarpa seedling was increased by 15.7–21.2% and 8.5–20.4%, respectively compared to non-inoculated seedlings. In contrast, AMF inoculation minimally influenced the root biomass of the two tree species. The easily extractable glomalin (EEG) content and mean weight diameter (MWD) of rhizospheric soil of the inoculated seedlings increased by 28.9–75.1% and 31.7–48.1%, respectively compared to control. The AMF colonization was highly correlated with WSA>0.25, EEG and MWD. Overall results support our hypothesis that AMF colonization enhance the quantity of rhizospheric soil aggregates and improve the growth of host seedlings. We conclude that planting tree species inoculated with AMF has a potential for restoration of degraded karst ecosystem. In future research other locally adapted tree and shrub species should be tested following AMF inoculation to prepare a wider planting stocks to be used in restoration of degraded karsts.

Plant‐mycorrhizae association affects plant diversity, biomass, and soil nutrients along temporal gradients of natural restoration after farmland abandonment in the Loess Plateau, China

AbstractThe interaction between plants and arbuscular mycorrhizal fungi in the rhizosphere plays a vital role in driving vegetation recovery and restoration of soil nutrients. However, how this interaction affects vegetation succession and how soil nutrient recovery is driven by vegetation restoration and rhizosphere processes are still largely unknown. In this study, a well‐documented grassland restoration chronosequence on the Loess Plateau, China (fields at 0, 7, 12, 17, 22, and 32 years after farmland abandonment and a natural grassland reference) was selected. The species richness and diversity reached maximum values between 17 and 22 years after farmland abandonment, whereas the plant total above and belowground biomasses simultaneously peaked at 22 years and then remained stable. In the dominant plant rhizosphere and bulk soil concentrations of total glomalin‐related soil protein (including both old and recently produced fungal proteins) substantially increased from 3.58 to 4.87 g kg−1 and from 2.67 to 3.86 g kg−1, respectively, between 12 and 32 years after farmland abandonment. The concentrations of soil organic carbon (SOC) and total nitrogen (TN) in the plant rhizosphere and bulk soil significantly increased between 17 and 32 years and reached the levels of the natural grassland. The aboveground plant biomass, soil SOC, and TN concentrations were positively correlated with the glomalin‐related soil protein (GRSP) concentration (p < .05). Our study suggested that interactions among plant‐mycorrhizae association, plant diversity, and biomass promote GRSP and nutrient accumulation in the plant rhizosphere and bulk soil, and GRSP largely contributes to SOC stabilization and the accumulation of SOC and TN.

A preliminary examination of bacterial, archaeal, and fungal communities inhabiting different rhizocompartments of tomato plants under real-world environments

Plant microbiota is a key determinant of plant health and productivity. The composition and structure of plant microbiota varies according to plant tissue and compartment, which are specific habitats for microbial colonization. To investigate the structural composition of the microbiome associated with tomato roots under natural systems, we characterized the bacterial, archaeal, and fungal communities of three belowground compartments (rhizosphere, endosphere, and bulk soil) of tomato plants collected from 23 greenhouses in 7 geographic locations of South Korea. The microbial diversity and structure varied by rhizocompartment, with the most distinctive community features found in the endosphere. The bacterial and fungal communities in the bulk soil and rhizosphere were correlated with soil physicochemical properties, such as pH, electrical conductivity, and exchangeable cation levels, while this trend was not evident in the endosphere samples. A small number of core bacterial operational taxonomic units (OTUs) present in all samples from the rhizosphere and endosphere represented more than 60% of the total relative abundance. Among these core microbes, OTUs belonging to the genera Acidovorax, Enterobacter, Pseudomonas, Rhizobium, Streptomyces, and Variovorax, members of which are known to have beneficial effects on plant growth, were more relatively abundant in the endosphere samples. A co-occurrence network analysis indicated that the microbial community in the rhizosphere had a larger and more complex network than those in the bulk soil and endosphere. The analysis also identified keystone taxa that might play important roles in microbe-microbe interactions in the community. Additionally, profiling of predicted gene functions identified many genes associated with membrane transport in the endospheric and rhizospheric communities. Overall, the data presented here provide preliminary insight into bacterial, archaeal, and fungal phylogeny, functionality, and interactions in the rhizocompartments of tomato roots under real-world environments.

Production and characterization of antimicrobials from isolate Pantoea agglomerans of Medicago sativa plant rhizosphere soil

Due to rise in drug resistance among pathogens, there is always an urge to look for new drug alternatives. So in this study we aimed to identify the unexplored rhizosphere microflora of alfalfa plant for new antimicrobials. With initial screening for isolates from rhizosphere region for antibacterial activity against selected bacterial pathogens, the isolate AL10 had better activity selected for this study. The isolate mass was cultured and secondary metabolites were extracted using ethyl acetate and subjected to FTIR and GC-MS analysis. Based on functional diversity analysis, the isolate subjected to anti-bacterial activity revealed significant activity against Streptococcus pneumonia, Klebsiella, S. aureus with zone of inhibition in the range of18-20 mm. Based on GC-MS analysis report ten compounds were identified and 1-Octadecane and 1-nonadecanol were found to be responsible for bio-activity. FT-IR results showed that N-H stretching functional group was dominantly present in the extract. Molecular identification of the isolate by 16S rRNA sequencing showed the isolate as Pantoea agglomerans. The results showed that the isolate P.agglomerans, gram negative bacteria had wide antibacterial activity due to 1-Octadecane and 1-nonadecanol. Though Alfalfa plant has been described for various biological activities, this is a first report on rhizosphere region of plant reporting for antibacterial potential microbes.

Three New Isoflavonoid Glycosides from the Mangrove-Derived Actinomycete Micromonospora aurantiaca 110B.

The mangrove ecosystem is a rich resource for the discovery of actinomycetes with potential applications in pharmaceutical science. Besides the genus Streptomyces, Micromonospora is also a source of new bioactive agents. We screened Micromonospora from the rhizosphere soil of mangrove plants in Fujian province, China, and 51 strains were obtained. Among them, the extracts of 12 isolates inhibited the growth of human lung carcinoma A549 cells. Strain 110B exhibited better cytotoxic activity, and its bioactive constituents were investigated. Consequently, three new isoflavonoid glycosides, daidzein-4′-(2-deoxy-α-l-fucopyranoside) (1), daidzein-7-(2-deoxy-α-l-fucopyranoside) (2), and daidzein-4′,7-di-(2-deoxy-α-l-fucopyranoside) (3) were isolated from the fermentation broth of strain 110B. The structures of the new compounds were determined by spectroscopic methods, including 1D and 2D nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectrometry (HR-ESIMS). The result of medium-changing experiments implicated that these new compounds were microbial biotransformation products of strain M. aurantiaca 110B. The three compounds displayed moderate cytotoxic activity to the human lung carcinoma cell line A549, hepatocellular liver carcinoma cell line HepG2, and the human colon tumor cell line HCT116, whereas none of them showed antifungal or antibacterial activities.

Plant species identity and soil characteristics determine rhizosphere soil bacteria community composition in European temperate forests.

Soil bacteria and understorey plants interact and drive forest ecosystem functioning. Yet, knowledge about biotic and abiotic factors that affect the composition of the bacterial community in the rhizosphere of understorey plants is largely lacking. Here, we assessed the effects of plant species identity (Milium effusum vs. Stachys sylvatica), rhizospheric soil characteristics, large-scale environmental conditions (temperature, precipitation and nitrogen (N) deposition), and land-use history (ancient vs. recent forests) on bacterial community composition in rhizosphere soil in temperate forests along a 1700 km latitudinal gradient in Europe. The dominant bacterial phyla in the rhizosphere soil of both plant species were Acidobacteria, Actinobacteria and Proteobacteria. Bacterial community composition differed significantly between the two plant species. Within plant species, soil chemistry was the most important factor determining soil bacterial community composition. More precisely, soil acidity correlated with the presence of multiple phyla, e.g. Acidobacteria (negatively), Chlamydiae (negatively) and Nitrospirae (positively), in both plant species. Large-scale environmental conditions were only important in S. sylvatica and land-use history was not important in either of the plant species. The observed role of understorey plant species identity and rhizosphere soil characteristics in determining soil bacterial community composition extends our understanding of plant-soil bacteria interactions in forest ecosystem functioning.

Antagonistic activity of the Streptomyces species isolated from rhizospheric soil of selected medicinal important plants.

A total eleven streptomyces species were isolated from the plant rhizosphere soils. Extract were prepared by using Mineral medium and tested for their antibacterial activity against the Enterobacteriaceae members. Seven isolates (63%) of the streptomyces extracts were active against five pathogenic bacteria. 5 isolates (45%) of the Streptomyces extracts doesn’t showed any activity against the 5 pathogenic organisms. 80% of the inhibition was showed by strain no 6 & 10 in the organisms E. coli , K. pneumoniae and S. flexineri . 70-75% of inhibition was showed by strain no 3, 4, 5 and 11 on the organisms K. pneumoniae, S. typhi, E. coli and S. flexineri .

Isolation, Evaluation and Molecular Identification of Streptomyces Isolates with Antimicrobial Activities

Out of sixteen Streptomyces sp. isolates were isolated from root rhizosphere soil of tomato plants. Four isolates coded; C1, 8SW, 30SW and 11SA were selected as the highest antibiotic productivity. The highest records of the antibiotic productivity were 21 and 25 mm as inhibition zones obtained from the original strains 8SW and 11SA after 10 days using E. coli DH-5α as a tester. The highest records of the antibiotic productivity were 12 mm and 11 mm when used Aspergillus niger and Saccharomyces cerevisiae as testers. Three of the four tested Streptomyces isolates i.e. C1, 8SW and 11SA exhibited highly inhibited (31 mm) of the two fungal plant pathogens. Using RAPD and SRAP marker the clustering of tested isolates were different from each other, RAPD marker could be grouped isolates (C1 and 8SW), (30SW and 11SA) to two clusters. However, SRAP grouped isolates (C1, 8SW and 30SW) in one cluster, however isolate 11SA clustered separately. Based on DNA sequences using 16S rDNA the data showed that isolates C1 and 8SW belonged to Streptomyces albidoflavus andisolates 30SW and 11SA were belonged to Streptomyces bobbili. For more accuracy the isolate C1 aligned with all Streptomyces in gene bank and confirmed in belonged to S. albidoflavus.

Bacterial community diversity associated with the severity of bacterial wilt disease in tomato fields in southeast China.

Tomato bacterial wilt caused by Ralstonia solanacearum is a devastating plant disease. The aims of this study were to investigate the relationship among soil nutrients, rhizobacterial community, and abundance of R. solanacearum, and to gather useful information for controlling the disease. Fifteen tomato rhizosphere soils were collected from three regions, encompassing five disease grades. Then, soil physicochemical properties and rhizobacterial communities were investigated. The content of soil organic carbon (SOC), total phosphorus (TP), total potassium (TK), and exchangeable calcium was significantly higher in the healthy plant rhizosphere soils than in diseased plant rhizosphere soils (P < 0.05). The healthy soils had a relatively higher abundance of Proteobacteria and a lower abundance of Acidobacteria than the diseased soils from the same region. Redundancy analysis demonstrated that R. solanacearum abundance was positively correlated with total nitrogen content and negatively correlated with soil pH, SOC, TP, TK, and exchangeable calcium. Ralstonia solanacearum abundance correlated positively with Chloroflexi, Acidobacteria, and Planctomycetes abundance but negatively with Nitrospirae, Bacteroidetes, and Proteobacteria abundance. These results suggested that improving soil pH, applying the amount of P and K fertilizers, and controlling the dosage of N fertilizer might be an effective approach in controlling bacterial wilt disease.

Highly connected taxa located in the microbial network are prevalent in the rhizosphere soil of healthy plant

The microbial community in the rhizosphere soil highly affects plant health and vice versa. However, the differences in soil microbial communities associated with different pathogenic statuses in the same field and their causes have not been comprehensively investigated. Here, we deciphered the dissimilarities in the rhizosphere soils of lisianthus (Eustoma grandiflorum) with different pathogenic statuses in a field under uniform management strategies at multiple scales. The rhizosphere soils of diseased plants harbored higher bacterial abundances and diversities compared to that of healthy plants. The relative abundances of three keystone operational taxonomic units (OTUs) and cumulative relative abundance of members in the central module (the largest module) of microbial network significantly decreased by 51.1%, 49.4%, 47.6%, and 42.0% in the rhizosphere soil of infected plants and by 64.3%, 58.8%, 63.4%, and 61.8% in that of dying plants, while the relative abundances of Flavobacteriales, Sphingobacteriales, and Xanthomonadales significantly increased to 4.89-, 1.88-, and 1.44-fold in the rhizosphere soil of infected plants and to 2.89-, 1.55-, and 1.66-fold in that of dying plants, respectively compared with that of healthy plants. Some human disease-related pathways and fluorescein diacetate hydrolysis were more prevalent in the rhizosphere soils of diseased plants. Stochastic processes contributed more than 50.6% and 86.4% to the assembly of different bacterial and fungal communities in these soils, and plants further shaped the bacterial communities, compared to fungal communities, probably by actively recruiting some potential suppressive agents in their rhizosphere when attacked by the pathogen. Overall, here, we firstly reported that the keystone taxa and members in the central module were enriched in the rhizosphere soil of healthy plants, which might be a potential indicator for the soil supporting plant health.