• Journal of Microbiology and Biotechnology
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• 제21권8호
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• pp.777-790
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• 2011

To elucidate the biodiversity of plant growth-promoting rhizobacteria (PGPR) in Korea, 7,638 bacteria isolated from the rhizosphere of plant species growing in many different regions were screened. A large number of PGPR were identified by testing the ability of each isolate to promote the growth of cucumber seedlings. After redundant rhizobacteria were removed via amplified rDNA restriction analysis, 90 strains were finally selected as PGPR. On the basis of 16S ribosomal RNA sequences, 68 Gram-positive (76%) and 22 Gram-negative (24%) isolates were assigned to 21 genera and 47 species. Of these genera, Bacillus (32 species) made up the largest complement, followed by Paenibacillus (19) and Pseudomonas (11). Phylogenetic analysis showed that most of the Grampositive PGPR fell into two categories: low- and high- G+C (Actinobacteria) strains. The Gram-negative PGPR were distributed in three categories: ${\alpha}$-proteobacteria, ${\beta}$- proteobacteria, and ${\gamma}$-proteobacteria. To our knowledge, this is the largest screening study designed to isolate diverse PGPR. The enlarged understanding of PGPR genetic diversity provided herein will expand the knowledge base regarding beneficial plant-microbe interactions. The outcome of this research may have a practical effect on crop production methodologies.

• Mycobiology
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• 제43권4호
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• pp.444-449
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• 2015

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in the rhizosphere and form symbiotic relationships with most terrestrial plant roots. In this study, four strains of Rhizophagus clarus were cultured and variations in their growth characteristics owing to functional diversity and resultant effects on host plant were investigated. Growth characteristics of the studied R. clarus strains varied significantly, suggesting that AMF retain high genetic variability at the intraspecies level despite asexual lineage. Furthermore, host plant growth response to the R. clarus strains showed that genetic variability in AMF could cause significant differences in the growth of the host plant, which prefers particular genetic types of fungal strains. These results suggest that the intraspecific genetic diversity of AMF could be result of similar selective pressure and may be expressed at a functional level.

• Journal of Applied Biological Chemistry
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• 제64권4호
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• pp.333-341
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• 2021

In this study, to select strains suitable as microbial agent from among rhizosphere microorganisms present in rhizosphere soil and roots, the mineral solubilization ability, antifungal activity against 10 types of plant pathogenic fungi, and plant growth-promoting activity of rhizosphere microorganisms were evaluated. As a result, DDP346 was selected because it has solubilization ability of phosphoric acid, calcium carbonate, silicon, and zinc; nitrogen fixing ability; production ability of siderophore, indole-3-acetic acid, and aminocyclopropane-1-carboxylate deaminase; and antifungal activity against seven types of plant pathogenic fungi. DDP346 showed a 99.9% homology with Acinetobacter pittii DSM 21653 (NR_117621.1); phylogenetic analysis also revealed a close relationship with Acinetobacter pittii based on the 16S rRNA base sequence. The growth conditions of DDP346 were identified as temperatures in the range of 10-40 ℃, pH in the range of 5-11, and salt concentrations in the range of 0-5%. In addition, a negative correlation coefficient (r² = -0.913, p <0.01) was shown between pH change and the solubilized phosphoric acid content of Acinetobacter sp. DDP346, and this is assumed to be due to the organic acid generated during culture. Consequently, through the evaluation of its mineral solubilization ability, antifungal activity against plant pathogenic fungi, and plant growth-promoting activity, the potential for the utilization of Acinetobacter sp. DDP346 as a multi-purpose microbial agent is presented.

• Korean Journal of Environmental Agriculture
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• 제40권1호
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• pp.49-59
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• 2021

BACKGROUND: Soil salinity causes reduction of crop productivity. Rhizosphere microbes have metabolic capabilities and ability to adaptation of plants to biotic and abiotic stresses. Plant growth-promoting bacteria (PGPB) could play a role as elicitors for inducing tolerance to stresses in plants by affecting resident microorganism in soil. This study was conducted to demonstrate the effect of selected strains on rhizosphere microbial community under salinity stress. METHODS AND RESULTS: The experiments were conducted in tomato plants in pots containing field soil. Bacterial suspension was inoculated into three-week-old tomato plants, one week after inoculation, and -1,000 kPa-balanced salinity stress was imposed. The physiological and biochemical attributes of plant under salt stress were monitored by evaluating pigment, malondialdehyde (MDA), proline, soil pH, electrical conductivity (EC) and ion concentrations. To demonstrate the effect of selected Bacillus strains on rhizosphere microbial community, soil microbial diversity and abundance were evaluated with Illumina MiSeq sequencing, and primer sets of 341F/805R and ITS3/ITS4 were used for bacterial and fungal communities, respectively. As a result, when the bacterial strains were inoculated and then salinity stress was imposed, the inoculation decreases the stress susceptibility including reduction in lipid peroxidation, enhanced pigmentation and proline accumulation which subsequently resulted in better plant growth. However, bacterial inoculations did not affect diversity (observed OTUs, ACE, Chao1 and Shannon) and structure (principle coordinate analysis) of microbial communities under salinity stress. Furthermore, relative abundance in microbial communities had no significant difference between bacterial treated- and untreated-soils under salinity stress. CONCLUSION: Inoculation of Bacillus strains could affect plant responses and soil pH of tomato plants under salinity stress, whereas microbial diversity and abundance had no significant difference by the bacterial treatments. These findings demonstrated that Bacillus strains could alleviate plant's salinity damages by regulating pigments, proline, and MDA contents without significant changes of microbial community in tomato plants, and can be used as effective biostimulators against salinity stress for sustainable agriculture.

• Korean Journal of Soil Science and Fertilizer
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• 제43권4호
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• pp.514-521
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• 2010

Fertilizers, plant growth promoting microbes and plant growth regulators should be combined together and used in order to achieve a maximal plant growth and yield in modern sustainable and ecological agricultural systems. In this study rhizosphere inoculation of Methylobacterium oryzae CBMB20 and foliar application of methanol were tested for their ability to promote the growth of red pepper plant at different levels of organic fertilizer. Rhizosphere inoculation of M. oryzae CBMB20 and foliar spray of methanol could promote red pepper plant growth and yield, and the growth promoting effect induced by the combined treatment of M. oryzae CBMB20 inoculation and foliar spray of methanol was more distinctive. This result suggests that a synergistic growth promoting effect of methanol spray and M. oryzae CBMB20 inoculation can be obtained in the combined treatment of the two growth promoting factors. The growth promoting effect was more significant in the lower fertilization rate, and the plant growth was not significantly different between 100 and 300% fertilizer treatments where both M. oryzae CBMB20 inoculation and foliar spray of methanol were included. This result indicates that, with the plant growth promoting effect of M. oryzae CBMB20 and methanol, fertilizer application rate can be profoundly reduced without any significant decreases in biomass accumulation and yield of crops.

• Microbiology and Biotechnology Letters
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• 제37권1호
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• pp.1-9
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• 2009

The genetic monitoring method was developed for the rapid detection of the PGPR and biocontrol agent, B. subtilis AH18 in red-pepper field soil by multiplex PCR using sid, aec and cel gene primers. The monitoring of B. subtilis AH18 in the soil was carried by amplified a 2,3-dihydro-2,3-dihydroxy benzoate dehydrogenase [EC: 1. 3. 1. 28]gene (sid - 794 bp : EF408238) which is a key enzyme of siderophore synthesis, an auxin efflux carrier gene (aec - 1,052 bp : EF408239) and a cellulase gene (cel - 1,582 bp : EF070194). The natural un sterilized soil was inoculated with B. subtilis AH18 to determine the sensitivity ($1.8\times10^5$ cfu/g) of multiplex PCR for the rapid dectection and then the strain was monitored successfully in rhizosphere or non-rhizosphere soil of red-pepper cultural soil. At 3 weeks after the treatment, density of the strain was monitored more abundantly in rhizosphere soil.

• Journal of Microbiology and Biotechnology
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• 제30권8호
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• pp.1169-1179
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• 2020

In this study, two soybean genotypes, i.e., aluminum-tolerant Baxi 10 (BX10) and aluminumsensitive Bendi 2 (BD2), were used as plant materials and acidic red soil was used as growth medium. The soil layers from the inside to the outside of the root are: rhizospheric soil after washing (WRH), rhizospheric soil after brushing (BRH) and rhizospheric soil at two sides (SRH), respectively. The rhizosphere bacterial communities were analyzed by high-throughput sequencing of V4 hypervariable regions of 16S rRNA gene amplicons via Illumina MiSeq. The results of alpha diversity analysis showed that the BRH and SRH of BX10 were significantly lower in community richness than that of BD2, while the WRH exhibited no significant difference between BX10 and BD2. Among the three sampling compartments of the same soybean genotype, WRH had the lowest community richness and diversity while showing the highest coverage. Beta diversity analysis results displayed no significant difference for any compartment between the two genotypes, or among the three different sampling compartments for any same soybean genotype. However, the relative abundance of major bacterial taxa, specifically nitrogen-fixing and/or aluminum-tolerant bacteria, was significantly different in the compartments of the BRH and/or SRH at phylum and genus levels, indicating genotype-dependent variations in rhizosphere bacterial communities. Strikingly, as compared with BRH and SRH, the WRH within the same genotype (BX10 or BD2) always had an enrichment effect on rhizosphere bacteria associated with nitrogen fixation.

• Asian Journal of Turfgrass Science
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• 제18권2호
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• pp.97-104
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• 2004

Anaerobic soils limit the amount of free oxygen available in the rhizosphere and therefore will impede grass root development and restrain nutrient availability for turf growth. An in-situ study was conducted on existing greens to investigate the relationship between $CO_2$ content in the rhizosphere and turf quality. Nine greens were selected in the study. On each green, five 1-m diameter circular plots were randomly selected for conducting the experiment. The greens were sampled 7 times from August, 1998 to August, 1999. Data collected from each plot included turf quality index, $CO_2$ content, and physical properties of the rooting mixtures. Turf quality declined drastically when $CO_2$ content in rhizosphere increased to $5\;to\;6{\mu}LL^{-1}$ during the late summer season. The $CO_2$ content increased as water content in the root zone increased, but was inversely related to infiltration rate. Cultivation of a golf green may reduce $CO_2$ content in the rhizosphere, but the benefit of cultivation decreased with time.

• Journal of Applied Biological Chemistry
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• 제54권2호
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• pp.120-125
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• 2011

In order to exploit Methylobacterium oryzae CBMB20 as of plant growth promoting agent, different inoculation methods have been evaluated. The present study aimed to evaluate soil, foliar, and soil+foliar inoculations of M. oryzae CBMB20 to improve the growth, fruit yield, and nutrient uptake of red pepper (Capsicum annuum L.) under greenhouse conditions. The population range of green fluorescent protein (gfp)-tagged M. oryzae CBMB20 using the three inoculation methods was 2.5-2.9 ${\log}_{10}$ cfu/g in the rhizosphere and 4.5-6.0 ${\log}_{10}$ cfu/g in the phyllosphere of red pepper plants. Confocal laser scanning microscopy results confirmed the colonization of M. oryzae CBMB20 endophytically on leaf surface. Plant height, fruit dry weight, and total biomass were significantly higher ($p{\leq}0.05$) in all M. oryzae CBMB20 inoculation methods as compared to non-inoculated control. Furthermore, uptake of mineral nutrients such as N, P, K, Ca, and Mg in red pepper plants in all M. oryzae CBMB20 inoculation methods was higher than in non-inoculated control. Comparative results of inoculation methods clearly demonstrated that soil+foliar inoculation of M. oryzae CBMB20 lead to the highest biomass accumulation and nutrient uptake which may be due to its efficient colonization in the red pepper rhizosphere and phyllosphere.

• Molecules and Cells
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• 제37권2호
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• pp.109-117
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• 2014

Microbiota in the niches of the rhizosphere zones can affect plant growth and responses to environmental stress conditions via mutualistic interactions with host plants. Specifically, some beneficial bacteria, collectively referred to as Plant Growth Promoting Rhizobacteria (PGPRs), increase plant biomass and innate immunity potential. Here, we report that Enterobacter sp. EJ01, a bacterium isolated from sea china pink (Dianthus japonicus thunb) in reclaimed land of Gyehwa-do in Korea, improved the vegetative growth and alleviated salt stress in tomato and Arabidopsis. EJ01 was capable of producing 1-aminocy-clopropane-1-carboxylate (ACC) deaminase and also exhibited indole-3-acetic acid (IAA) production. The isolate EJ01 conferred increases in fresh weight, dry weight, and plant height of tomato and Arabidopsis under both normal and high salinity conditions. At the molecular level, short-term treatment with EJ01 increased the expression of salt stress responsive genes such as DREB2b, RD29A, RD29B, and RAB18 in Arabidopsis. The expression of proline biosynthetic genes (i.e. P5CS1 and P5CS2) and of genes related to priming processes (i.e. MPK3 and MPK6) were also up-regulated. In addition, reactive oxygen species scavenging activities were enhanced in tomatoes treated with EJ01 in stressed conditions. GFP-tagged EJ01 displayed colonization in the rhizosphere and endosphere in the roots of Arabidopsis. In conclusion, the newly isolated Enterobacter sp. EJ01 is a likely PGPR and alleviates salt stress in host plants through multiple mechanisms, including the rapid up-regulation of conserved plant salt stress responsive signaling pathways.