• Journal of Microbiology and Biotechnology
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• v.31 no.10
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• pp.1373-1382
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• 2021

Plant growth promoting rhizobacteria (PGPR) are a group of bacteria that can increase plant growth; but due to unfavorable environmental conditions, PGPR are biologically unstable and their survival rates in soil are limited. Therefore, the suitable application of PGPR as a plant growth stimulation is one of the significant challenges in agriculture. This study presents an intelligent formulation based on Bacillus velezensis VRU1 encapsulation enriched with nanoparticles that was able to control Rhizoctonia solani on the bean. The spherical structure of the capsule was observed based on the Scanning Electron Microscope image. Results indicated that with increasing gelatin concentration, the swelling ratio and moisture content were increased; and since the highest encapsulation efficiency and bacterial release were observed at a gelatin concentration of 1.5%, this concentration was considered in mixture with alginate for encapsulation. The application of this formulation which is based on encapsulation and nanotechnology appears to be a promising technique to deliver PGPR in soil and is more effective for plants.

• Korean Journal of Agricultural Science
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• v.50 no.4
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• pp.759-771
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• 2023

Plant growth-promoting rhizobacteria (PGPR) are naturally occurring bacteria that intensively colonize plant roots and are crucial in promoting the crop growth. These beneficial microorganisms have garnered considerable attention as potential bio-inoculants for sustainable agriculture. PGPR directly interacts with plants by providing essential nutrients through nitrogen fixation and phosphate solubilization and accelerating the accessibility of other trace elements such as Cu, Zn, and Fe. Additionally, they produce plant growth-promoting phytohormones, such as indole acetic acids (IAA), indole butyric acids (IBA), gibberellins, and cytokinins.PGPR interacts with plants indirectly by protecting them from diseases and infections by producing antibiotics, siderophores, hydrogen cyanide, and fungal cell wall-degrading enzymes such as glucanases, chitinases, and proteases. Furthermore, PGPR protects plants against abiotic stresses such as drought and salinity by producing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and modulating plant stress markers. Bacteria belonging to genera such as Bacillus, Pseudomonas, Burkholderia, Pantoa, and Enterobacter exhibit multiple plant growth-promoting traits, that can enhance plant growth directly, indirectly, or through synergetic effects. This comprehensive review emphasizes how PGPR influences plant growth promotion and presents promising prospects for its application in sustainable agriculture.

• Journal of Microbiology and Biotechnology
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• v.17 no.8
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• pp.1300-1307
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• 2007

This study assessed the possible role of different traits in selected plant growth-promoting rhizobacteria (PGPR) for improving wheat growth and yield under natural conditions. Rhizobacteria exhibiting 1-aminocyclopropane-1-carboxylate (ACC)-deaminase activity were isolated and screened for their growth-promoting activity in wheat under axenic conditions. Five isolates belonging to Pseudomonas and one Burkholderia caryophylli isolate that showed promising performances under axenic conditions were selected and characterized for in vitro ACC-deaminase activity, chitinase activity, auxin production, P solubilization, and root colonization. These isolates were then used as inocula for wheat cultivated under natural conditions in pot and/or field trials. Significant increases in root elongation, root weight, tillers per pot, 1,000-grain weight, and grain and straw yields were observed in response to inoculation with PGPR in the pot trials. Inoculation with these PGPR was also effective under field conditions and increased the wheat growth and yield significantly. However, the efficacy of the strains was inconsistent under the axenic, pot, and field conditions. Pseudomonas fluorescens ($ACC_{50}$), which exhibited a relatively high in vitro ACC-deaminase activity, chitinase activity, auxin production, and P solubilization and more intensive root colonization, was the most efficient isolate under the field conditions. Therefore, these results demonstrated that ACC-deaminase activity is an efficient parameter for the selection of promising PGPR under axenic conditions. However, additional traits of PGPR, including auxin production, chitinase activity, P solubilization, and root colonization, are also important for selecting PGPR as biofertilizers.

• Microbiology and Biotechnology Letters
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• v.34 no.2
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• pp.83-93
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• 2006

In heavily industrialized areas, soil sites are contaminated with high concentrations of heavy metals. These pollutants are highly accumulated to the human body through the food web and cause serious diseases. To remove heavy metals from the soil, a potential strategy is the environmental friendly and cost effective phytoremediation. For the enhancement of remediation efficiency, the symbiotic interaction between the plant and plant growth-promoting rhizobacteria (PGPR) has been attended. In this review, the interaction of the plant and PGPR in the heavy metal-contaminated soil has been reviewed. The physicochemical and biological characteristics of the rhlzosphere can influence directly or indirectly on the biomass, activity and population structure of the rhizobacteria. The root exudates are offered to the soil microbes as useful carbon sources and growth factors, so the growth and metabolism of rhizobacteria can be promoted. PGPR have many roles to lower the level of growth-inhibiting stress ethylene within the plant, and also to provide iron and phosphorus from the soil to plant, and to produce phytohormone such as indole acetic acid. The plant with PGPR can grow better in the heavy metal contaminated soil. Therefore higher efficiency of the phytoremediation will be expected by the application of the PGPR.

• Korean Journal of Soil Science and Fertilizer
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• v.42 no.spc
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• pp.20-28
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• 2009

The sustainability of conventional agriculture which is characterized by input dependent and ecologically simplified food production system is vague. Chemicals and present practices used in agriculture are not only costly but also have widespread implications on human and animal health, food quality and safety and environmental quality. Thus there is a need for alternative farming practices to sustain food production for the escalating population and conserve environment for future generations. The present research scenario in the area of plant microbe interactions for maintaining sustainable agriculture suggests that the level of internal regulation in agro-ecosystems is largely dependent on the level of plant and microbial diversity present in the soil. In agro-ecosystems, biodiversity performs a variety of ecological services beyond the production of food, including recycling of nutrients, regulation of microclimate and local hydrological processes, suppression of undesirable organisms and detoxification of noxious chemicals. Controlling the soil microflora to enhance the predominance of beneficial and effective microorganisms can help improve and maintain soil chemical and physical properties. The role of beneficial soil microorganisms in sustainable productivity has been well construed. Some plant bacteria referred to as plant growth-promoting rhizobacteria (PGPR) can contribute to improve plant growth, nutrient uptake and microbial diversity when inoculated to plants. Term PGPR was initially used to describe strains of naturally occurring non-symbiotic soil bacteria have the ability to colonize plant roots and stimulate plant growth PGPR activity has been reported in strains belonging to several other genera, such as Azotobacter, Azospirillum, Arthrobacter Bacillus, Burkhokderia, Methylobacterium, and Pseudomonas etc. PGPR stimulate plant growth directly either by synthesizing hormones such as indole acetic acid or by promoting nutrition, for example, by phosphate solubilization or more generally by accelerating mineralization processes. They can also stimulate growth indirectly, acting as biocontrol agents by protecting the plant against soil borne fungal pathogens or deleterious bacteria. Present review focuses on some recent developments to evolve strategies for better biotechnological exploitation of PGPR's.

• The Plant Pathology Journal
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• v.25 no.4
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• pp.389-399
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• 2009

A group of beneficial plant bacteria has been shown to increase crop growth referring to as plant growth-promoting rhizobacteria (PGPR). PGPR can decrease plant disease directly, through the production of antagonistic compounds, and indirectly, through the elicitation of a plant defense response termed induced systemic resistance (ISR). While the mechanism of PGPR-elicited ISR has been studied extensively in the model plant Arabidopsis, it is less well characterized in crop plants such as pepper. In an effort to better understand the mechanism of ISR in crop plants, we investigated the induction of ISR by Bacillus cereus strain BS107 against Xanthomonas axonopodis pv. vesicatoria in pepper leaves. We focused on the priming effect of B. cereus strain BS107 on plant defense genes as an ISR mechanism. Of ten known pepper defense genes that were previously reported to be involved in pathogen defense signaling, the expression of Capsicum annum pathogenesis-protein 4 and CaPR1 was systemically primed by the application of strain BS107 onto pepper roots confirming by quantitative-reverse transcriptase PCR. Our results provide novel genetic evidence of the priming effect of a rhizobacterium on the expression of pepper defense genes involved in ISR.

• Journal of Microbiology and Biotechnology
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• v.22 no.1
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• pp.13-24
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• 2012

The genetic diversity of plant growth-promoting rhizobacterial (PGPR) fluorescent pseudomonads associated with the sugarcane (Saccharum officinarum L.) rhizosphere was analyzed. Selected isolates were screened for plant growthpromoting properties including production of indole acetic acid, phosphate solubilization, denitrification ability, and production of antifungal metabolites. Furthermore, 16S rDNA sequence analysis was performed to identify and differentiate these isolates. Based on 16S rDNA sequence similarity, the isolates were designated as Pseudomonas plecoglossicida, P. fluorescens, P. libaniensis, and P. aeruginosa. Differentiation of isolates belonging to the same group was achieved through different genomic DNA fingerprinting techniques, including randomly amplified polymorphic DNA (RAPD), amplified ribosomal DNA restriction analysis (ARDRA), repetitive extragenic palindromic (REP), enterobacterial repetitive intergenic consensus (ERIC), and bacterial repetitive BOX elements (BOX) analyses. The genetic diversity observed among the isolates and rep-PCR-generated fingerprinting patterns revealed that PGPR fluorescent pseudomonads are associated with the rhizosphere of sugarcane and that P. plecoglossicida is a dominant species. The knowledge obtained herein regarding the genetic and functional diversity of fluorescent pseudomonads associated with the sugarcane rhizosphere is useful for understanding their ecological role and potential utilization in sustainable agriculture.

• The Plant Pathology Journal
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• v.29 no.2
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• pp.201-208
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• 2013

Drought stress is one of the major yield affecting factor for pepper plant. The effects of PGPRs were analyzed in relation with drought resistance. The PGPRs inoculated pepper plants tolerate the drought stress and survived as compared to non-inoculated pepper plants that died after 15 days of drought stress. Variations in protein and RNA accumulation patterns of inoculated and non-inoculated pepper plants subjected to drought conditions for 10 days were confirmed by two dimensional polyacrylamide gel electrophoresis (2D-PAGE) and differential display PCR (DD-PCR), respectively. A total of six differentially expressed stress proteins were identified in the treated pepper plants by 2D-PAGE. Among the stress proteins, specific genes of Cadhn, VA, sHSP and CaPR-10 showed more than a 1.5-fold expressed in amount in B. licheniformis K11-treated drought pepper compared to untreated drought pepper. The changes in proteins and gene expression patterns were attributed to the B. licheniformis K11. Accordingly, auxin and ACC deaminase producing PGPR B. licheniformis K11 could reduce drought stress in drought affected regions without the need for overusing agrochemicals and chemical fertilizer. These results will contribute to the development of a microbial agent for organic farming by PGPR.

• Microbiology and Biotechnology Letters
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• v.49 no.3
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• pp.374-383
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• 2021

Rhizoctonia solani is one of the major pathogens that cause sheath blight disease in rice. Sheath blight is one of the most difficult diseases to control. Biological control (with the use of rhizobacteria) is one of the ways to control this disease. Plant Growth Promoting Rhizobacteria (PGPR) is a rhizosphere bacterium that can be used to enhance plant growth. The composition of the rhizobacteria in organic and nonorganic soil is affected by the chemical characteristics of the soil - which influences plant physiology and root exudation patterns. This study aimed to obtain a species of rhizobacteria which shows PGPR activity, from organic and nonorganic rice fields and test their capability to suppress R. solani growth. Out of 23 isolates screened for PGPR activity, the following isolates showed high PGPR activity and were selected for in vitro antagonistic activity testing against R. solani: ISO6, ISO11, ISO15, ISN2, ISN3, and ISN7, The six isolates produced 43,42-75,23 ppm of IAA, possessed phosphorus solubilization capability, and chitinase-producing activity. ISO6 (54.88%) and ISN7 (83.33%) displayed high inhibition capacities against R. solani, in vitro. ISO6 and ISN7 inhibited the growth of R. solani lesions on rice leaves by 89% and 100% (without lesion), respectively, after 7 days of incubation. Analysis of their 16S rRNA sequences revealed that the ISO6 isolate was Citrobacter freundii and ISN7 isolate was Pseudomonas aeruginosa.

• Korean Journal of Soil Science and Fertilizer
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• v.45 no.4
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• pp.582-592
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• 2012

Microorganisms present in the rhizosphere soil plays a vital role in improving the plant growth and soil fertility. Many kinds of fertilizers including chemical and organic has been approached to improve the productivity. Though some of them showed significant improvement in yield, they failed to maintain the soil properties. Rather they negatively affected soil eventually, the land became unsuitable for agricultural. To overcome these problems, microorganisms have been used as effective alternative. For past few decades, plant growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) have been used as effective inoculants to enhance the plant growth and productivity. PGPR improves the plant growth and helps the plant to withstand biotic and abiotic stresses. AM fungi are known to colonize roots of plants and they increase the plant nutrient uptake. Spore associated bacteria (SAB) are attached to spore wall or hyphae and known to increase the AMF germination and root colonization but their mechanism of interaction is poorly known. Better understanding the interactions among AMF, SAB and PGPR are necessary to enhance the quality of inoculants as a biofertilizers. In this paper, current knowledge about the interactions between fungi and bacteria are reviewed and discussed about AMF spore associated bacteria.