Root Endophytic Bacteria Research Articles

Frequency of Endophytic Bacteria in Roots and Foliage of Brachiaria Humídicola Cv. Humidicola (Rendle) Schweick in Soil with Arsenic Presence

The objective of this study was to correlate the presence of arsenic in roots and stems of Brachiaria humidicola cv. humidicola (Rendle) Schweick grown in cattle areas of the San Jorge subregion and the population density of endophytic bacteria in roots and foliage with the presence of this metal. Samples of soil, roots and stems of B. humicola grass were collected and characterized for arsenic concentration in roots and foliage and the presence of endophytic bacteria (CFU/g tissue). The results show the presence of arsenic concentrations in roots and stems above the values established at national and international level. Likewise, the presence of endophytic bacteria was found in the roots and foliage of B. humidicola, which may be contributing to the remediation and reduction of arsenic concentration from the roots to the foliage. This is the first study correlating the presence of arsenic and endophytic bacteria on cattle farms with B. humicola and the possible role of these bacteria in contributing to bioremediation of this metal in the soil and within the tissues of the pasture species.

Evaluation of the Amount of Endophytic Bacteria Associated with Roots of Brachiaria Humidicola Cv. Humidicola (Rendle) Schweick in Relation to Ph Values, Organic Matter and Phosphorus Contents of Cattle Farm Soil

The objective of this study was to isolate endophytic bacteria from roots of Brachiaria humidicola cv. humidicola (Rendle) Schweick and to relate their presence to pH, organic matter and phosphorus contents of the soil of cattle farms located in the municipality of San Benito Abad. Soil sampling was carried out with roots of B. humicola for the isolation and counting of the population density of endophytic bacteria and soil samples were also collected for the determination of pH, organic matter and phosphorus parameters. The results found indicate that there is an amount of endophytic bacteria in roots of B. humidicola when the soil contains optimum pH values of (6.1 ± 6.98); low to moderate phosphorus content (10.8 ± 16.28 mg/kg) and low to moderate organic matter content (1.7 ± 2.31%). The presence of endophytic bacteria was observed in a range of 3.0 ± 8.0 X 106 CFU/g of roots. There is a worldwide need to establish a relationship between endophytic bacteria and soil physical-chemical quality indicator parameters to predict a change in functional diversity under physical, chemical and biological conditions of the soil ecosystem.

High-throughput 16S rRNA gene-based amplicon sequencing reveals the functional divergence of halophilic bacterial communities in the Suaeda salsa root compartments on the eastern coast of China

The rhizosphere environment of plants, which harbors halophilic bacterial communities, faces significant challenges in coping with environmental stressors, particularly saline soil properties. This study utilizes a high-throughput 16S rRNA gene-based amplicon sequencing to investigate the variations in bacterial community dynamics in rhizosphere soil (RH), root surface soil (RS), root endophytic bacteria (PE) compartments of Suaeda salsa roots, and adjoining soils (CK) across six locations along the eastern coast of China: Nantong (NT), Yancheng (YC), Dalian (DL), Tianjin (TJ), Dongying (DY), and Qingdao (QD), all characterized by chloride-type saline soil. Variations in the physicochemical properties of the RH compartment were also evaluated. The results revealed significant changes in pH, electrical conductivity, total salt content, and ion concentrations in RH samples from different locations. Notably, the NT location exhibited the highest alkalinity and nitrogen availability. The pH variations were linked to HCO3− accumulation in S. salsa roots, while salinity stress influenced soil pH through H+ discharge. Despite salinity stress, enzymatic activities such as catalase and urease were higher in soils from various locations. The diversity and richness of bacterial communities were higher in specific locations, with Proteobacteria dominating PE samples from the DL location. Additionally, Vibrio and Marinobacter were prevalent in RH samples. Significant correlations were found between soil pH, salinity, nutrient content, and the abundance and diversity of bacterial taxa in RH samples. Bioinformatics analysis revealed the prevalence of halophilic bacteria, such as Bacillus, Halomonas, and Streptomyces, with diverse metabolic functions, including amino acid and carbohydrate metabolisms. Essential genes, such as auxin response factor (ARF) and GTPase-encoding genes, were abundant in RH samples, suggesting adaptive strategies for harsh environments. Likewise, proline/betaine transport protein genes were enriched, indicating potential bioremediation mechanisms against high salt stress. These findings provide insight into the metabolic adaptations facilitating resilience in saline ecosystems and contribute to understanding the complex interplay between soil conditions, bacterial communities, and plant adaptation.

Comparing the population density, colony diversity, and phosphate solubilization ability between rice root endophytic and rice rhizospheric soil bacteria from organic wetland

Abstract Phosphate-solubilizing bacteria (PSB) play important roles in the agricultural systems. The present study aims to compare the population density, colony diversity, and phosphate solubilization ability between rice root endophytic bacteria (RRoEB) and rice rhizospheric soil bacteria (RRzSB) from organic wetland. By spread plate method, bacteria were isolated directly using Pikovskaya’s agar and indirectly through other media, namely Nutrient Agar (NA), Starch Casein Agar (SCA), Jensen, and Yeast Extract Mannitol Agar (YEMA). Each distinct colony based on the morphology on the respective media was screened for phosphate solubilization ability by subculturing on Pikovskaya’s agar. The phosphate solubilizing index (PSI) was measured from the halo zone formation. The results showed that by direct isolation, 6 RRoEB and 5 RRzSB were able to phosphate solubilization. By indirect isolation from NA, SCA, Jensen, and YEMA, 2, 3, 1, and 3 isolates of RRoEB and 4, 3, 1, and 3 isolates of RRzSB showed the capability as phosphate solubilizer. Although the highest colony diversity of PSB was obtained from direct isolation, however the highest PSI was yielded from indirect isolation, namely isolates J1R1 (3.53) and Y1S1 (2.48). The highest PSI from direct isolation was obtained by P1R5 (1.90) and P1S1 (1.51).

Chitinase Enzyme-Producing Endophytic Bacterias From the Roots of the Plant Gembolo (Dioscorea bulbifera): Isolation, Characterization and its Potential as an Antifungal Agent

Chitinase is an enzyme of the chitinolytic group that has many roles in agriculture, especially as an antifungal, because chitin is one of the constituent components of the fungal cell wall. This study aimed to isolate and identify endophytic bacteria from gembolo (Dioscorea bulbifera) roots and to characterize the chitinase enzyme from these endophytic bacteria to be used as an antifungal. Isolation and identification of gembolo plant root endophytic bacteria using PCR method of 16S rRNA gene amplification and sequencing. Characterization of the chitinase enzyme produced includes determining of optimum pH, temperature, and substrate UV-Vis spectrophotometer. Antagonistic test of the chitinase enzyme and endophytic bacterial isolates (isolate K4) Fusarium oxysporum. The results showed that bacterial isolate K4 had with chitinolytic index of 2.45 mm. Electrophoresis results with PCR 16s rRNA gene; the length of the amplified fragment is the position of 1300 bp. By doing the BLAST process in GenBank, the bacterial isolate has 97.93% similarity with Enterobacter cloacae. Then, this endophytic bacteria is called Enterobacter cloacae K4-G. This bacterium produced chitinase enzyme reaching maximum chitinase activity at the 38 hours with an activity of 0.0312 U/mL. The chitinase characterization results of E. cloacae K4-G showed that the optimum conditions were reached at at pH 6, temperature 45 ᵒC, and 2.5% substrate with a chitinase activity value of 0.2467 U/mL. Chitinase enzyme and bacteria Enterobacter cloacae K4-G can inhibit the growth of the fungus Fusarium oxysporum. Therefore, Chitinase from Enterobacter cloacae K4-G can be used as an antifungal pathogen in plants.
 
 Keywords: Chitinase, endophytic bacteria, Enterobacter cloacae

Diversity of endophytic bacterial community in rice roots and their roles in phosphate solubilization and plant growth

Root endophytic bacteria have significant beneficial effects on plant growth and health, while specific coexisting pathogenic bacteria can cause various diseases. In this study, we assessed the diversity and cultivability of the endophytic bacterial community in rice roots with a focus on their capacity for phosphate solubilization and impact on plant growth. Employing PacBio Single Molecule Real-Time (SMRT) and Sanger sequencing, we generated 16S rRNA gene libraries using metagenomic DNA extracted from the roots of three field-grown rice plants, along with genomic DNA from 156 associated bacterial isolates. QIIME 2-based microbiome analysis revealed dominant classified species at diverse taxonomic levels, including Arcobacter marinus, Paraburkholderia kururiensis, Lactobacillus plantarum, and Lactobacillus brevis. Furthermore, we effectively isolated 25.97% of rice root endophytic bacteria, with a notable 33.33% of pure culture endophytic bacteria exhibiting phosphate solubilization abilities. Finally, we revealed the inhibitory role of Burkholderia vietnamiensis and the growth promoting role of Paraburkholderia kururiensis subsp. Kururiensis in both the monocot model Brachypodium distachyon and the dicot Arabidopsis thaliana. Our study provided novel insight into the microbiome structure in rice roots and its potential to benefit rice cultivation and enhance overall crop health.

Effects of different dwarfing interstocks on the rhizosphere, endophytic bacteria, and drought resistance of apple trees

Rootstock is commonly used to enhance plant resistance to drought stress. However, it is necessary to investigate the effects of different rootstock, interstock, and scion combinations on rhizosphere and root endophytic bacteria under drought stress. We conducted a pot experiment to investigate how interstock [SH40, Jizhen 1 (J1), and Jizhen 2 (J2)] affects the drought tolerance and nitrogen (N) uptake and utilization of apple trees under drought stress. The results showed that the total dry weight, total chlorophyll content, carotenoid content, photosynthesis rate, and N absorption and utilization efficiency of apple trees decreased significantly, whereas relative electrolyte leakage increased significantly under drought stress. Membership function analysis showed that the apple plants with the J1 interstock had the greatest drought resistance. In addition, drought treatment significantly affected the diversity and composition of rhizosphere and root endophytic communities in all three rootstock/interstock/scion combinations. Further analysis revealed that the relative abundance of the plant pathogen Ralstonia was significantly increased in J2 drought-treated roots, compared to the other groups, whereas those of some potentially beneficial bacteria (0134_terrestrial_group, Phenylobacterium, Ellin6067, Kribbella, Chloronema, and Streptomyces) increased significantly in the J1 drought-treated sample. Co-occurrence network analysis showed that some potentially beneficial bacteria (Ellin6067, S0134_terrestrial_group, Pedomicrobium, and Subgroup_10) were significantly positively correlated with N content. These modifications of the rhizosphere and endophytic bacterial communities may influence the drought resilience and N uptake efficiency of different combinations of interstocks and scions. This study is a much-needed step towards understanding the stress response mechanism of scion–rootstock combinations.

Melatonin alleviates cadmium toxicity by regulating root endophytic bacteria community structure and metabolite composition in apple.

The level of cadmium (Cd) accumulation in orchard soils is increasing, and excess Cd will cause serious damage to plants. Melatonin is a potent natural antioxidant and has a potential role in alleviating Cd stress. This study aimed to investigate the effects of exogenous melatonin on a root endophyte bacteria community and metabolite composition under Cd stress. The results showed that melatonin significantly scavenged the reactive oxygen species and restored the photosynthetic system (manifested by the improved photosynthetic parameters, total chlorophyll content and the chlorophyll fluorescence parameters (Fv/Fm)), increased the activity of antioxidant enzymes (the activities of catalase, superoxide dismutase, peroxidase and ascorbate oxidase) and reduced the concentration of Cd in the roots and leaves of apple plants. High-throughput sequencing showed that melatonin increased the endophytic bacterial community richness significantly and changed the community structure under Cd stress. The abundance of some potentially beneficial endophytic bacteria (Ohtaekwangia, Streptomyces, Tabrizicola and Azovibrio) increased significantly, indicating that the plants may absorb potentially beneficial microorganisms to resist Cd stress. The metabolomics results showed that melatonin significantly changed the composition of root metabolites, and the relative abundance of some metabolites decreased, suggesting that melatonin may resist Cd stress by depleting root metabolites. In addition, co-occurrence network analysis indicated that some potentially beneficial endophytes may be influenced by specific metabolites. These results provide a theoretical basis for studying the effects of melatonin on the endophytic bacterial community and metabolic composition in apple plants.

Influences of plant organ, genotype, and cultivation site on the endophytic bacteriome of maize (Zea mays L.) in the semi-arid region of Pernambuco, Brazil.

Endophytic bacteria play a crucial role in plant development and adaptation, and the knowledge of how endophytic bacteria assemblage is influenced by cultivation site and plant genotype is an important step to achieve microbiome manipulation. This work aimed to study the roots and stems of endophytic bacteriome of four maize genotypes cultivated in two regions of the semi-arid region of Pernambuco - Brazil. Our hypothesis is that the endophytic community assemblage will be influenced by plant genotypes and cultivation region. Metabarcoding sequencing data revealed significant differences in alfa diversity in function of both factors, genotypes, and maize organs. Beta diversity analysis showed that the bacterial communities differ mainly in function of the plant organ. The most abundant genera found in the samples were Leifsonia, Bacillus, Klebsiella, Streptomyces, and Bradyrhizobium. To understand ecological interactions within each compartment, we constructed co-occurrence network for each organ. This analysis revealed important differences in network structure and complexity and suggested that Leifsonia (the main genera found) had distinct ecological roles depending on the plant organ. Our data showed that root endophytic maize bacteria would be influenced by cultivation site, but not by genotype. We believe that, collectively, our data not only characterize the bacteriome associated with this plant and how different factors shape it, but also increase the knowledge to select potential bacteria for bioinoculant production.

Effect of endophytic bacteria on the phytoremediation potential of halophyte Tamarix smyrnensis for Sb-contaminated soils

Phytoremediation, including bacteria-assisted phytoremediation, presents a promising technology for treating shooting range soils contaminated with toxic metalloids. In this study, a pot experiment was performed using the halophyte Tamarix smyrnensis and soil collected from a shooting range and artificially spiked at two different antimonite (Sb(III)) concentrations (50 mg/kg and 250 mg/kg) with the aim to explore the Sb phytoremediation of the halophyte. The effect of salt (0.3%) and Mn addition (300 ppm) on its remediation capacity was also investigated. Moreover, the root endophytic community of the halophyte was found able to remove Sb(III) and was periodically inoculated to the plants. The consortium application increased the Sb bioavailable fraction in the soil and enhanced the Sb accumulation in root and aerial parts (up to 50% and 55% respectively at high Sb(III) concentration) compared to the uninoculated plants. Moreover, the presence of Mn increased the translocation factor (21% increase for inoculated and 46% increase for uninoculated plants) while lower TF was observed at high Sb concentrations (0,2 and 0,07 was the lowest value at low and high Sb treatments respectively). The addition of salt, Mn and root endophytic bacteria aided the halophyte to cope with elevated Sb concentrations. The total chlorophyll concentration was higher in inoculated plants compared to the uninoculated ones in all treatments, implying the positive effects of endophytic inoculation. The halophyte T. smyrnensis with the aid of endophytic community presents a promising alternative for remediating shooting range soils especially in areas impacted by salinity.

Assessment of the role of ACC deaminase, IAA, and siderophore-producing bacteria isolated from Spratly Islands on the growth of Brassica juncea on the coral sand

Root endophytic and rhizosphere bacteria play a significant role in enhancing plant tolerance and promoting growth by producing 1-aminocyclopropane-1-carboxylate (ACC) deaminase, indole-3-acetic acid (IAA), and siderophore. These bacteria have been isolated and screened from 45 plants’ roots and rhizosphere soil samples of 19 types of plants which are growing on 8 floating islands in Spratley Islands, Viet Nam. In which, 3 root endophytic bacteria strains were selected and identified to be Agrobacterium tumefaciens, Pseudomonas plecoglossicida, and Klebsiella aerogenes from roots of Scaevola taccada, Barringtonia asiatica (L.) Kurz, and Carica papaya, respectively. Correspondingly, 3 rhizosphere bacteria strains were selected and identified to be Bacillus velezensis, Bacillus aryabhattai, and Bacillus velezensis from rhizosphere soils of Canavalia maritima (Aubt) Thouars (C. obtusifolia DC.), Cucumis sativus, Heliotropium foertherianum, respectively. These strains were found could increase the germination rate of Brassica juncea’s seeds and 20-day-old fresh biomass, compared to the control treatment in the same condition of 10‰ saline watering. When these bacterial strains were combined as an inoculant, they indicated the same result on coral sand. Thus, the addition of selected endophytic and rhizosphere bacteria is efficient in improving the coral sand environment to enhance food crops’ development in the Spratly Islands.

Carbon nanosol-induced assemblage of a plant-beneficial microbiome consortium

Carbon nanosol (CNS) is a carbon-based nanomaterial that promotes plant growth; however, its functional mechanisms and effects on the microbiome are not fully understood. Here, we explored the effects of CNS on the relationship between the soil, endophytic microbiomes and plant productivity. CNS treatment increased the fresh biomass of tobacco (Nicotiana tabacum L.) plants by 27.4% ± 9.9%. Amplicon sequencing analysis showed that the CNS treatment significantly affected the composition and diversity of the microbial communities in multiple ecological niches associated with tobacco, especially the bulk soil and stem endophytic microbiome. Furthermore, the application of CNS resulted in enhanced network connectivity and stability of the microbial communities in different niches, particularly in the soil, implying a strengthening of certain microbial interactions. Certain potentially growth-promoting root endophytic bacteria were more abundant under the CNS treatment. In addition, CNS increased the abundance of some endophytic microbial functional genes known to enhance plant growth, such as those associated with nutrient metabolism and the plant hormone biosynthesis pathways. We isolated two bacterial strains (Sphingopyxis sp. and Novosphingobium sp.) that were enriched under CNS treatment, and they were confirmed to promote tobacco plant growth in vitro. These results suggested that CNS might, at least in part, promote plant growth by enriching beneficial bacteria in the microbiome.Graphical

Metal phytostabilization by mastic shrub (Pistacia lentiscus L.) and its root-associated bacteria in different habitats of Sardinian abandoned mining areas (Italy).

Pistacia lentiscus L. is an excluder metallophyte proposed for the revegetation and phytostabilization of metal-contaminated sites in the Mediterranean area. The present study aims at evaluating the linking between bacterial communities and plants spontaneously growing in ecosystems chronically impacted by mining activities. Environmental properties and metal accumulation into hypogeal and epigeal tissues were analyzed in wild plants of two contrasting habitats with extreme metal contamination (> 2300mg/kg for Zn, > 1100mg/kg for Pb, > 10mg/kg for Cd). The community structures of rhizospheric and root endophytic bacteria were fingerprinted by terminal restriction fragment length polymorphism of the 16S rRNA gene. The wild shrubs efficiently restrict the accumulation of the three major contaminants to the epigeal tissues in the two habitats under study (249 ± 68mg/kg dw for Zn, 43 ± 21mg/kg dw for Pb, and 1.4 ± 0.5mg/kg dw for Cd). Evidence was provided that the combined but not individual effect of environmental conditions (moisture, inorganic carbon, pH) and proportion between Zn and Cd in the mine substrate play a role in structuring rhizosphere bacterial communities. The observed changes in community structures of root endophytes were found to be strongly associated with Pb level in roots and substrate properties (inorganic carbon and Zn/Cd ratio). Overall, our study highlights the importance of the analysis of multifactorial interactions among mine substrate, plant, and microbes for understanding how the environmental context affects phytoremediation under real conditions.

Shifts in the diversity of root endophytic microorganisms across the life cycle of the ratooning rice Jiafuzhan.

The diversity of root endophytic microorganisms, which is closely related to plant life activities, is known to vary with the plant growth stage. This study on the ratooning rice Jiafuzhan explored the diversity of the root endophytic bacteria and fungi and their dynamics during the plant life cycle. By sequencing the 16S ribosomal ribonucleic acid (16S rRNA) and internal transcribed spacer (ITS) genes, 12,154 operational taxonomic units (OTUs) and 497 amplicon sequence variants (ASVs) were obtained, respectively. The root endophytic microorganisms of rice in the seedling, tillering, jointing, heading, and mature stages of the first crop and at 13, 25, and 60 days after regeneration (at the heading, full heading, and mature stages of the second crop, respectively) were analyzed using diversity and correlation analyses. There were significant differences in the α-diversity and β-diversity of root endophytic bacteria and fungi in the growth stage. Additionally, linear discriminant analysis (LDA) effect size (LEfSe) analysis revealed biomarker bacteria for each growth stage, but biomarker fungi did not exist in every stage. Moreover, the correlation analysis showed that the bacterial and fungal biomarkers interacted with each other. Furthermore, the nitrogen-fixing genus Bradyrhizobium existed in all growth stages. These findings indicate the pattern of root endophytic microorganisms of ratooning rice at different growth stages, and they provide new insights into the high yield of the second crop of ratooning rice (in light of the abundance of various bacteria and fungi).

Bioprospection of single and a consortium endophytic bacteria of suboptimal field rice isolates as biocontrol of rice bacterial leaf blight pathogens

Abstract. Djatmiko HA, Prihatiningsih N, Lestari P. 2023. Bioprospection of single and a consortium endophytic bacteria of suboptimal field rice isolates as biocontrol of rice bacterial leaf blight pathogens. Biodiversitas 24: 2710-2715. Rice root endophytic bacteria isolated from suboptimal land have the potential to control leaf blight by Xanthomonas oryzae pv. oryzae (Xoo). The aim of this research was: 1) to test the potential of single and consortium endophytic bacteria single and consortium to control Xoo in vitro, 2) to know the antibiosis mechanism of this endophytic bacteria and 3) to evaluate the biochemical character of the single endophytic bacteria as an antagonist feature. The completely randomized design with 5 single and 1 consortium treatment, 4 replications was used as a research method. The inhibition was carried out using a diffusion method of 108 cfu/mL endophytic bacterial suspension. Filter paper 6 mm diameter had been dripped 10 µL suspension of endophytic bacteria, then it placed 3 spots on NA that had been poured with Xoo. The variable observed was the inhibition zone of endophytic bacteria, the inhibition mechanism, and the character as antagonist produces protease; and siderophore. The results showed that both single and consortium endophytic bacteria could potentially suppress Xoo in-vitro, and the best inhibition was the consortium with an inhibitory area of ??62.74 mm2 and the bacteriostatic mechanism. The consortium's antibiosis index was 1.49, it can produce protease and siderophore with clear zone and orange color features. The endophytic bacteria consortium has the potential as a biopesticide to be developed as an alternative to control rice bacterial leaf blight.

Response mechanism of interaction between Rhododendron hainanense and microorganisms to heat stress

Heat stress is a major limitation to Rhododendron cultivation in tropical and subtropical regions. Microbial community plays an important role in plant resistance to heat stress, however the microbial mechanism is poorly understood. We conducted a pot culture experiment on Rhododendron hainanense to reveal the mechanism of root microorganisms and soil microorganisms in response to heat stress, using an artificial climate simulation. The experimental control (CK) was set as day (25 ℃, 14 h) /night (20 ℃, 10 h), treatments were medium temperature stress (MTS, 35/30 ℃), and severe temperature stress (STS, 40/35 ℃). The result showed that compared with CK, MTS treatment considerably increased malondialdehyde content, and STS treatment significantly increased proline, and both heat stress treatments significantly decreased chlorophyll content. In comparison to CK, MTS considerably reduced soil nitrate nitrogen, soil microbial biomass carbon, and soil water-soluble organic carbon content. STS dramatically increased soil available nitrogen, soil water-soluble organic carbon, and soil microbial biomass carbon. Heat stress also significantly affected soil microbial community and root endophytic microbial community. Soil microbial and root bacterial community significantly correlated with soil nitrate nitrogen content, and root endophytic fungi significantly correlated with proline and soilwater-soluble organic carbon content. Therefore, soil microorganisms impacted soil nitrogen availability under heat stress, root endophytic bacteria impacted the ability of R. hainanense to absorb nitrogen, and root endophytic fungi controlled the physiological traits of R. hainanense by modifying Pro content to increase the resistance of R. hainanense to heat stress.

Beneficial effects of selected rhizospheric and endophytic bacteria, inoculated individually or in combination, on non-native host plant development

Plant beneficial bacteria have been traditionally inoculated as unique strains, although combining bacteria with complementary traits could maximize their positive effect on plant growth and development. Our objective was to elaborate consortia from selected rhizospheric and endophytic bacteria with antifungal and plant growth promoting properties, and evaluate their beneficial effects on the growth of Physalis ixocarpa, an annual native Mexican species of horticultural importance. Bacterial strains were selected based on their antifungal activity against Fusarium spp. through in vitro antagonism assays. Characterization of the profile of volatile organic compounds (VOC) of newly-identified endophytic strains able to significantly inhibit Fusarium spp. evidenced the presence of sulfur compounds and ketones, reported for their antifungal activity. Seven bacterial strains were able to solubilize phosphate on NBRIP medium. Their capacity to promote the growth of A. thaliana in vitro was further tested. All stains stimulated the formation of lateral roots and root hairs, and enhanced A. thaliana biomass, most likely through auxin production. Twelve consortia were elaborated from rhizospheric and root endophytic bacteria, and the effects of consortia and individual strain inoculation on the growth and development of P. ixocarpa were evaluated in a greenhouse trial. Rhizobacterial strains A8a and 5911, and consortia formed by A8a + B3R7 and SO + B3R7 (all belonging to the Bacillus genus) showed the best results in terms of growth promotion and floral onset, with increases in plant height by up to 45% and flowering beginning 30 days before than in the Control. Our results confirm the potential of combining rhizospheric and endophytic bacteria with multiple beneficial traits for enhancing plant development and suggest that the most promising bacterial treatments could be applied to avocado trees, their natural host, to foster their productivity.

Effects of fertilizer reduction coupled with straw returning on soil fertility, wheat root endophytic bacteria, and the occurrence of wheat crown rot.

Excessive fertilization is associated with nutrient loss, soil compaction, and weak plant resistance. Straw returning can increase soil fertility with a consequent reduction in fertilizer, but the effects of fertilizer reduction coupled with straw returning on crop endophytic microbes and crop disease are poorly understood. Therefore, using metagenomic sequencing methods we investigated the responses of soil fertility, diversity, the function of root endophytic bacteria, and the occurrence of wheat crown rot due to the application of fertilizer (no, moderate and excessive fertilizer) coupled with or without straw returning after 7 years of treatments. The results showed that, after excessive fertilization, the wheat crown rot became severe, registering a disease index of 23. Compared with excessive fertilization, moderate fertilization coupled with straw returning significantly reduced the incidence of wheat crown rot, the disease index was reduced by 38.50%, and the richness and diversity of endophytic bacteria were increased by 61.20 and 11.93%, respectively, but the soil fertility was not significantly affected. In addition, moderate fertilization coupled with straw returning changed the community structure of endophytic bacteria and increased the relative abundance of carbohydrate metabolism and nitrogen fixation-related genes by 4.72 and 9.32%, respectively. Our results indicated that fertilizer reduction coupled with straw returning reduced the occurrence of wheat crown rot, increased the diversity of endophytic bacteria, and changed the community structure and function of endophytic bacteria, which will provide a better understanding of the interaction of fertilization coupled with straw returning, endophytic bacteria and wheat crown rot.

Quantification and Diversity of Cultivated Bacteria in Root Endosphere and Rhizosphere of Bamboo Species Fargesia nitida in Association with the Tree Succession

Fargesia nitida is a cold-resistant evergreen bamboo and is a pioneer plant in the secondary succession after the native trees were destroyed in the eastern Tibetan Plateau. However, little is known about the effects of this plant on soil conditions and about its microbiomes. Aiming at learning the interactions among the soil characteristics, the plants and the microbes in relation to the plant succession, a study on cultivated microbes associated with the rhizocompartments of F. nitida was performed in the present study to reveal the preference of this plant to the root associated microbes, in comparison with that associated with the successive spruce (Picea asperata Mast.) trees. The results demonstrated that growth of F. nitida could improve the soil nutrient contents, especially increasing total nitrogen, NH4+-N, total carbon, and microbial biomass carbon, and maintained more soil bacteria than the successive spruce trees. Based upon the study of F. nitida root-associated cultivated microbial community, the nutrient improvement in F. nitida growing soils might be from the root endophytic bacteria, which presented greater abundance (3.8, 1.7, and 12.6 folds) than that of bacteria in its rhizosphere, root zone soil, and spruce root zone soil, respectively. Pseudomonas members, especially species related to P. baetica and P. vancouverensis, were strongly selected by F. nitida as root endophytes.

Drought stress modifies the community structure of root-associated microbes that improve Atractylodes lancea growth and medicinal compound accumulation.

Atractylodes lancea is an important medicinal plant in traditional Chinese medicine, its rhizome is rich of volatile secondary metabolites with medicinal values and is largely demanded in modern markets. Currently, supply of high-yield, high-quality A. lancea is mainly achieved via cultivation. Certain soil microbes can benefit plant growth, secondary metabolism and induce resistance to environmental stresses. Hence, studies on the effects of soil microbe communities and isolates microorganisms on A. lancea is extremely meaningful for future application of microbes on cultivation. Here we investigated the effects of the inoculation with an entire soil microbial community on the growth, resistance to drought, and accumulation of major medicinal compounds (hinesol, β-eudesmol, atractylon and atractylodin) of A. lancea. We analyzed the interaction between A. lancea and the soil microbes at the phylum and genus levels under drought stress of different severities (inflicted by 0%, 10% and 25% PEG6000 treatments). Our results showed that inoculation with soil microbes promoted the growth, root biomass yield, medicinal compound accumulation, and rendered drought-resistant traits of A. lancea, including relatively high root:shoot ratio and high root water content under drought. Moreover, our results suggested drought stress was more powerful than the selectivity of A. lancea in shaping the root-associated microbial communities; also, the fungal communities had a stronger role than the bacterial communities in protecting A. lancea from drought. Specific microbial clades that might have a role in protecting A. lancea from drought stress were identified: at the genus level, the rhizospheric bacteria Bacillus, Dylla and Actinomadura, and rhizospheric fungi Chaetomium, Acrophialophora, Trichoderma and Thielava, the root endophytic bacteria Burkholderia-Caballeronia-Paraburkholderia, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Dylla and Actinomadura, and the root endophytic fungus Fusarium were closely associated with A. lancea under drought stress. Additionally, we acquired several endophytic Paenibacillus, Paraburkholderia and Fusarium strains and verified they had differential promoting effects on the medicinal compound accumulation in A. lancea root. This study reports the interaction between A. lancea and soil microbe communities under drought stress, and provides insights for improving the outcomes in A. lancea farming via applying microbe inoculation.