Plant growth-promoting activities for bacterial and fungal endophytes isolated from medicinal plant of Teucrium polium L.

Endophytic microbes are ubiquitous in most plant species. Endophytic microbes enter plants mainly through wounds, naturally occurring as a result of plant growth or through root hairs and at epidermal conjunctions. Besides gaining entrance to plants through natural openings or wounds, endophytic microbes appear to actively penetrate plant tissues using hydrolytic enzymes like cellulase and pectinase. Diverse community structure of endophytes can be analyzed using culture-dependent and culture-independent method. Endophytic bacteria belong to different phyla such as Acidobacteria, Actinobacteria, Ascomycota, Bacteroidetes, Basidiomycota, Deinococcus-Thermus, and Firmicutes. Endophytic archaea (Euryarchaeota) were reported using only culture-independent method. Endophytic microbes were most predominant and studied and belonged to three major phyla Actinobacteria, Proteobacteria, and Firmicutes. Among reported genera Achromobacter, Bacillus, Burkholderia, Enterobacter, Herbaspirillum, Pantoea, Pseudomonas, Rhizobium, and Streptomyces were dominant in most host plants. Along with common endophytic microbial genera, there were many niche-specific microbial genera that have been reported from different host plants. Application of associative microbes for sustainable agriculture holds immense potential. Endophytic microbes are known to enhance growth and yield of plants by fixing atmospheric nitrogen and solubilization of phosphorus, potassium, and zinc; production of phytohormones (cytokinins, auxins, and gibberellins), ammonia, hydrogen cyanide, and siderophores; and possession of antagonistic activity as well as reducing the level of stress ethylene in host plants. Endophytes seem to contribute to plant fitness and development, displaying beneficial traits that can be exploited in agricultural biotechnology. The interactions between endophytes and plants can promote plant health and play a significant role in low-input sustainable agriculture for both food and nonfood crops. This chapter summarizes part of the work being done on endophytic microbes, including their isolation, identification, diversity, distribution, and applications for sustainable agriculture.

Endophytic Microbes in Crops: Diversity and Beneficial Impact for Sustainable Agriculture

Study of endophytic bacteria within plant seeds is very essential and meaningful on account of their heritability and versatility. This study investigated Bacillus bacterial communities within the seeds of four commercial tomato varieties, by 16S rRNA gene PCR-RFLP (restriction fragment length polymorphism). Phylogenetic analysis of 16S rRNA gene sequences indicated that the 22 representative isolates belonged to five species of genus Bacillus and the bacterial compositions showed remarkable differences among tomato varieties. Isolates exhibited multiple plant growth promoting (PGP) traits: 37 % of indole-3-acetic acid production; 37 % of phosphate solubilization; 24 % of siderophores production; 85 % of potential nitrogen fixation and 6 % of 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Isolate HYT-12-1 was shown to have highest ACC deaminase activity (112.02 nmol α-ketobutyrate mg⁻¹ protein h⁻¹) among the five ACC deamiase producing strains. 16S rRNA gene sequencing indicated that the isolate HYT-12-1 shared the highest sequence similarity (100 %) with B. subtilis. PGP experiments under gnotobiotic and greenhouse conditions revealed the ability of strain HYT-12-1 to enhance the growth of tomato seedlings. This is the first study to describe endophytic Bacillus communities within tomato seeds, and the results suggest that B. subtilis strain HYT-12-1 would have a great potential for industrial application as biofertilizer in the future.

Bacterial community compositions of tomato ( Lycopersicum esculentum Mill.) seeds and plant growth promoting activity of ACC deaminase producing Bacillus subtilis (HYT-12-1) on tomato seedlings

Abstract Improving and understanding the electrospinnability of native cellulose in room temperature ionic liquids (RTIL) have been a hot issue in recent years. In this study, the electrospinning of cellulose in a highly efficient RTIL of 1-allyl-3-methylimidazolium chloride (AMIMCl) was investigated. The introduction of co-solvent dimethyl sulfoxide (DMSO), which significantly decreased the surface tension, viscosity and entanglement density of the network and increased the conductivity of the spinning dope, contributed to a continuous jet. The problems lying in nonvolatility and the high ionic strength of the RTIL, which unavoidably led to the standing up vertically, adhesion and contractions of the wet fibers during the electrospinning process, were successfully resolved using a rotating copper-wire drum as a collector and solidifying the jet under high relative humidity. The water vapor played an important role in leading to “skin formation” which helped to stabilize the fibrous morphology, and finally smooth ultra-thin regenerated cellulose fibers were obtained. The combination of solvent system and collecting apparatus and conditions provided not only an effective method of producing ultra-thin native cellulose fibers on a large scale, but also a fundamental solution to other electrospinning systems with high ionic strength and nonvolatility. Measurements on WAXD and FT-Raman indicated that the electrospun cellulose fibers were almost amorphous with a little crystallization presented the polymorph of Type-II, which was totally different from the native cellulose with the dominated polymorph of Type-I.

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Electrospinning of native cellulose from nonvolatile solvent system

Electrospinning is an economical and relatively simple method to produce continuous and uniform nanofibers from almost any synthetic and many natural polymers. Because of the high specific surface area, tunable pore size, and flexibility, the nanofibrous membranes are finding an increasingly wide range of applications. Some particular attention has been devoted to antibacterial nanofibers for applications such as wound dressings. A variety of biocides, e.g., antibiotics, quaternary ammonium salts, triclosan, biguanides, (silver, titanium dioxide, and zinc oxide) nanoparticles and chitosan have been incorporated by various techniques into nanofibers that exhibit strong antibacterial activity in standard assays. However, the small diameters of the nanofibers also mean that the incorporated biocides are often burst released once the materials are submerged in an aqueous solution. Nevertheless, several strategies, such as core-sheath structure of the nanofiber, covalent bonding of the biocide on the fiber surface and adsorption of the biocide in nanostructures, can be utilized to sustain the release over several days. This review summarizes recent development in the fabrication of antibacterial nanofibers, the release profiles of the biocides and their applications in in vivo systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40797.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/app.40797

Electrospun antibacterial nanofibers: Production, activity, and in vivo applications

Endophytic bacteria have been found in virtually every plant studied, where they colonize the internal tissues of their host plant and can form a range of different beneficial relationships. The diversity of bacterial endophytes associated with ginseng plants of varying age levels in Korea was investigated. Fifty-one colonies were isolated from the interior of ginseng stems. Although a mixed composition of endophyte communities was recovered from ginseng based on the results of 16S rDNA analysis, bacteria of the genus Bacillus and Staphylococcus dominated in 1-year-old and 4-year-old plants, respectively. Phylogenetic analysis revealed four clusters: Firmicutes, Actinobacteria, α-Proteobacteria, and γ-Proteobacteria, with Firmicutes being predominant. To evaluate the plant growth promoting activities, 18 representative isolates were selected. Amplification of nifH gene confirmed the presence of diazotrophy in only two isolates. Half of the isolates solubilized mineral phosphate. Except four, all the other endophytic isolates produced significant amounts of indole acetic acid in nutrient broth. Iron sequestering siderophore production was detected in seven isolates. Isolates E-I-3 (Bacillus megaterium), E-I-4 (Micrococcus luteus), E-I-8 (B. cereus), and E-I-20 (Lysinibacillus fusiformis) were positive for most of the plant growth promoting traits, indicating their role in growth promotion of ginseng.

Diversity of endophytic bacteria in ginseng and their potential for plant growth promotion.

Effect of alkaline protease-producing Exiguobacterium sp. YS1 inoculation on the solubilization and bacterial community of waste activated sludge

Antimicrobial activity of cellulose-based nanofibers with different Ag phases

The objective of this work was to determine the shifts in the PCR-DGGE profiles of bacterial communities associated with the rhizosphere soil of ginseng at varying age levels. Differences in the dominance of intense DNA bands in the DGGE profile was observed over the age of the plants indicating the fluctuation in the microbial community structure. The bacterial orders of actinomycetales of Actinobacteria and Spingomonadales and Rhizobiales of α-Proteobacteria were predominant in the ginseng soil.

Young Joon Yu

Papers

Diversity of endophytic bacteria in ginseng and their potential for plant growth promotion.

Effect of alkaline protease-producing Exiguobacterium sp. YS1 inoculation on the solubilization and bacterial community of waste activated sludge

Antimicrobial activity of cellulose-based nanofibers with different Ag phases

Analysis of Bacterial Community in the Ginseng Soil Using Denaturing Gradient Gel Electrophoresis (DGGE)