• Korean Journal of Microbiology
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• v.50 no.1
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• pp.40-45
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• 2014

In order to increase the persistence of plant growth promoting rhizobacteria (PGPR) in rhizpsphere soil, the growth of tomato was examined after the application of Arthrobacter woluwensis ED immobilized in alginate bead, which was known as PGPR. When tomato seedlings were treated with A. woluwensis ED of $1{\times}10^6$ cells g $soil^{-1}$ and incubated for 30 days in a plant growth chamber, the shoot length, root length, fresh weight and dry weight of the grown tomato plants treated with the suspended inoculants significantly increased by 36.2, 59, 51.1, and 37.5%, respectively compared to those of the uninoculated control. The treatment of the immobilized bacteria increased those by 42, 67.4, 62.5, and 60.4%, respectively compared to those of the uninoculated control. Therefore, the enhancement of tomato growth by the treatment of the immobilized bacteria was higher than those by the suspended inoculants. The effects of the inoculation on indigenous bacterial community and the fate of the inoculated bacteria were monitored by denaturing gradient gel electrophoresis analysis. The DNA band intensity of A. woluwensis ED in the tomato rhizosphere treated with the suspended inoculants continuously decreased after the inoculation, but the band intensity in the tomato rhizosphere soils treated with the immobilized inoculants showed the maximum at 1 week after inoculation and the decreasing rate was less than that of the suspended inoculants, which indicated the longer maintenance of the immobilized bacteria at rhizosphere soils. Therefore, encapsulation of PGPR in alginate beads may be more effective than liquid inoculant for the plant growth promotion and survival of PGPR at plant rhizosphere.

• Journal of Microbiology and Biotechnology
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• v.24 no.1
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• pp.106-112
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• 2014

Very few plant growth-promoting rhizobacteria (PGPR) are known to produce gibberellins (GAs). The current study aimed to isolate a phytohormone-producing PGP rhizobacterium from soil and assess its potential to enhance plant growth. The newly isolated bacterium was identified as Leifsonia soli sp. SE134 on the basis of partial 16S ribosomal RNA gene sequence. Application of L. soli culture filtrate significantly increased the biomass, hypocotyl, and root lengths of cucumber seeds as compared with non-inoculated sole medium and distilled water treated controls. Furthermore, the PGPR culture was applied to the GA-deficient mutant rice cultivar Waito-C. Treatment with L. soli SE134 significantly increased the growth of Waito-C rice seedlings as compared with controls. Upon chromatographic analysis of L. soli culture, we isolated, detected and quantified different GAs; namely, $GA_1$ ($0.61{\pm}0.15$), $GA_4$ ($1.58{\pm}0.26$), $GA_7$ ($0.54{\pm}0.18$), $GA_8$ ($0.98{\pm}0.15$), $GA_9$ ($0.45{\pm}0.17$), $GA_{12}$ ($0.64{\pm}0.21$), $GA_{19}$ ($0.18{\pm}0.09$), $GA_{20}$ ($0.78{\pm}0.15$), $GA_{24}$ ($0.38{\pm}0.09$), $GA_{34}$ ($0.35{\pm}0.10$), and $GA_{53}$ ($0.17{\pm}0.05$). Plant growth promotion in cucumber, tomato, and young radish plants further evidenced the potential of this strain as a PGP bacterium. The results suggest that GA secretion by L. soli SE134 might prove advantageous for its ameliorative role in crop growth. These findings can be extended for improving the productivity of different crops under diverse environmental conditions.

• Journal of Microbiology and Biotechnology
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• v.25 no.7
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• pp.1119-1128
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• 2015

1-Aminocyclopropane-1-carboxylate (ACC) deaminase, which is encoded by some bacteria, can reduce the amount of ethylene, a root elongation inhibitor, and stimulate the growth of plants under various environmental stresses. The presence of ACC deaminase activity and the regulation of ACC in several rhizospheric bacteria have been reported. The nitrogen-fixing Pseudomonas stutzeri A1501 is capable of endophytic association with rice plants and promotes the growth of rice. However, the functional identification of ACC deaminase has not been performed. In this study, the proposed effect of ACC deaminase in P. stutzeri A1501 was investigated. Genome mining showed that P. stutzeri A1501 carries a single gene encoding ACC deaminase, designated acdS. The acdS mutant was devoid of ACC deaminase activity and was less resistant to NaCl and NiCl₂ compared with the wild-type. Furthermore, inactivation of acdS greatly impaired its nitrogenase activity under salt stress conditions. It was also observed that mutation of the acdS gene led to loss of the ability to promote the growth of rice under salt or heavy metal stress. Taken together, this study illustrates the essential role of ACC deaminase, not only in enhancing the salt or heavy metal tolerance of bacteria but also in improving the growth of plants, and provides a theoretical basis for studying the interaction between plant growth-promoting rhizobacteria and plants.

• Microbiology and Biotechnology Letters
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• v.40 no.2
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• pp.135-143
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• 2012

This study's aim is to isolate and characterize plant growth promoting Enterobacter species for the biological control of gray leaf spot in pepper. Screening was carried out from the rhizosphere of Agropyron tsukushiensi var. transiens (Hack.) Ohwi in Dok-do. Rhizobacterial isolates were partially identified by 16S rDNA sequencing and Enterobacter species were tested for plant growth promoting capabilities and the induction of systemic resistance in pepper against gray leaf spot caused by Stemphylium solani. Isolates were tested for production of indole-acetic acid and siderophore, and for phosphate solubilization. The application of isolates was effective in controlling gray leaf spot in pepper with E. asburiae (KNUC5007) and E. cancerogenes (KNUC5008 and KNUC5010) having the highest efficacy in reducing gray leaf spot severity. This is the first report of the biological control of gray leaf spot in pepper using rhizobacteria and it is hoped that this study will increase the utilization of Enterobacter species as plant growth promoters and biocontrol agents.

• Korean Journal of Soil Science and Fertilizer
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• v.42 no.1
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• pp.29-36
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• 2009

Fourteen bacterial strains were isolated from crop rhizosphere and identified as phosphate solubilizing bacteria (PSB) by 16S rRNA analysis. Only 3 strains exhibited a strong ability to solubilize insoluble phosphate in agar medium containing a hydroxyapatite. The rates of P solubilization by isolates were ranged from 200 and $2300\;mg\;L^{-1}$, which are inversely correlated with pH in culture medium. Furthermore, HPLC analyses reveal the production of organic acid from the culture filtrates of PSB. Among these, strain Acinetobacter sp. released only gluconic acid, Pseudomonas orientalis produced gluconic acid which was subsequently converted into 2-ketogluconic acid, and Enterobacter asburiae released acetic acid and succinic acid. On the other hand, P. orientalis and E. asburiae released $372\;mg\;L^{-1}$ and $191\;mg\;L^{-1}$ of IAA into broth culture, respectively, while Acinetobacter sp. did not produce IAA. Furthermore, in vivo study showed that plant growth promoting effect by bacteria generally seemed to be increased IAA production and phosphate solubilization.

• The Plant Pathology Journal
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• v.23 no.3
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• pp.203-209
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• 2007

Infection structures were observed using a fluorescence microscope at the penetration sites on the leaves of potato plants pre-inoculated with the bacterial strains Pseudomonas putida TRL2-3, Micrococcus luteus TRK2-2, and Flexibacteraceae bacterium MRL412, which mediated an induced systemic resistance on potato plants against late blight disease caused by Phytophthora infestans. In order to compare the infection structures on the leaves expressing systemic acquired resistance, the leaves of potato plants pre-treated with DL-3-amino butyric acid (BABA) were also observed after challenge inoculation with the same pathogen. The infection structures were investigated. The total number of germination and appressorium formation of P. infestans were counted. Furthermore, the frequencies of fluorescent epidermal cells at the penetration sites, which indicate a defense response of plant cell, were estimated. There were no differences on the germination rates of the fungal cysts among the untreated control, BABA pre-treated, and bacterial strains pre-inoculated plants. However, appressorium formation was slightly decreased on the leaves of BABA pre-treated plants compared to those of untreated as well as bacterial strains pre-inoculated plants. Furthermore, the frequencies of fluorescent cells of BABA pre-treated and bacterial strains pre-inoculated were higher than that of untreated plants, indicating an active defense reaction of the host cells against the fungal attack. On the other hand, the pre-treatment with BABA caused a stronger fluorescent of epidermal cells at the penetration sites compared to the pre-inoculation with the bacterial strains. Interestingly, the frequency of fluorescent cells by BABA, however, was lower than that by the bacterial strains. Based on the results it is suggested that the infection structures showing resistance reaction on the leaves of potato plants were different between by pre-inoculation with bacterial strains and by pre-treatment with BABA against the late blight pathogen.

• Journal of Microbiology and Biotechnology
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• v.29 no.5
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• pp.794-808
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• 2019

Bacillus velezensis strain WRN014 was isolated from banana fields in Hainan, China. Bacillus velezensis is an important member of the plant growth-promoting rhizobacteria (PGPR) which can enhance plant growth and control soil-borne disease. The complete genome of Bacillus velezensis WRN014 was sequenced by combining Illumina Hiseq 2500 system and Pacific Biosciences SMRT high-throughput sequencing technologies. Then, the genome of Bacillus velezensis WRN014, together with 45 other completed genome sequences of the Bacillus velezensis strains, were comparatively studied. The genome of Bacillus velezensis WRN014 was 4,063,541bp in length and contained 4,062 coding sequences, 9 genomic islands and 13 gene clusters. The results of comparative genomic analysis provide evidence that (i) The 46 Bacillus velezensis strains formed 2 obviously closely related clades in phylogenetic trees. (ii) The pangenome in this study is open and is increasing with the addition of new sequenced genomes. (iii) Analysis of single nucleotide polymorphisms (SNPs) revealed local diversification of the 46 Bacillus velezensis genomes. Surprisingly, SNPs were not evenly distributed throughout the whole genome. (iv) Analysis of gene clusters revealed that rich gene clusters spread over Bacillus velezensis strains and some gene clusters are conserved in different strains. This study reveals that the strain WRN014 and other Bacillus velezensis strains have potential to be used as PGPR and biopesticide.

• Korean Journal of Microbiology
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• v.53 no.4
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• pp.257-264
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• 2017

Pseudomonas veronii MS1 and P. migulae MS2 have several mechanisms of copper resistance and plant growth promoting capability, and also can alleviate abiotic stress in plant by hydrolysis of a precursor of stress ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) by ACC deaminase. In 4-week pot test for tomato growth in soil contained 700 mg/kg Cu, inoculation of MS1 and MS2 significantly increased root and shoot lengths, wet weight and dry weight of tomato plants compared to those of uninoculated control. The inoculated tomato plants contained less amounts of proline that can protect plants from abiotic stress, and malondialdehyde, an oxidative stress marker than those of control. ACC synthase genes, ACS4 and ACS6, and ACC oxidase genes, ACO1 and ACO4, both involved in ethylene synthesis, were strongly expressed in Cu stressed tomato, whereas significantly reduced in tomato inoculated with MS1 and MS2. Also, a gene encoding a metal binding protein metallothionein, MT2 showed similar expression pattern with above genes. All these results indicated that these rhizobacteria could confer Cu resistance to tomato plant under Cu stress and allowed a lower level of Cu stress and growth promotion.

• Journal of Mushroom
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• v.17 no.1
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• pp.12-18
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• 2019

An auxin-producing bacterium Yangsong-1 was isolated from a button mushroom bed in Chung cheongnam-do. The strain Yangsong-1 was classified as a novel strain of Arthrobacter enclensis based on a chemotaxonomic and phylogenetic analysis. The isolated A. enclensis Yangsong-1 was confirmed to produce indole-3-acetic acid (IAA), which is one of the auxin hormones. When the concentration of IAA was assessed by HPLC quantity analysis, the maximum concentration of IAA, $152.903mg\;L^{-1}$, was detected from the culture broth incubated in R2A medium containing 0.2% L-tryptophan for 48 h at $35^{\circ}C$. A negative relationship between IAA production and pH was estimated to show that the increase in IAA caused pH acidification of the culture. The effect of the supplement on L-tryptophan, a known precursor of IAA production, appeared to be at maximal production at 0.2% concentration and was rather reduced at concentration above 0.4%. To investigate the growth-promoting effects on the crops, the culture broth of A. enclensis Yangsong-1 was placed in water cultures and seed pots of mung beans and lettuce. In consequence, the adventitious root induction and root growth of mung beans and lettuce were 1.5 and 1.9 times higher, respectively, than those of the control.

• Journal of Applied Biological Chemistry
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• v.52 no.3
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• pp.116-120
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• 2009

We found out the new method of the consortium for the environmental friendly agriculture by 8 kinds of the selected antagonistic rhizobacteria. This research involved composition of mutual complementary consortium by each antagonistic function such as production of antibiotic, siderophore, antifungal cellulase and insoluble phosphate solubilization. The consortium No.11 among composed consortium candidates showed the most pepper growth promoting activity and Phytophthora blight suppression on the in vivo pot test of red-pepper plant. The consortium No. 11 is combination of PGPR Bacillus subtilis AH18 and Bacillus licheniformis K11. B. subtilis AH18 and B. licheniformis K11 both could produce the auxin, antifungal ${\beta}$-glucannase and siderophore. Also, they had mechanism for solubilization of insoluble phosphate. But, B. licheniformis K11 could produce the antibiotic of iturin which was able to inhibit Phytophthora capsici. We confirmed complementary noncompetitive mutualism between B. subtilis AH18 and B. licheniformis K11 of the consortium No.11. The results came out through treatment of two strains co-culture, treatment of individual culture and co-treatment of two individual cultures for the growth and Phytophthora blight suppression of red-pepper. The treatment of two strains co-culture didn't show a synergic effect in comparing sole treatment on the pepper growth promotion and Phytophthora blight suppression. But, when the pots were treated simultaneously with co-treatment of two individual cultures, an synergic effect was seen in the growth promotion of roots, stem, leaves and suppressed Phytophthora blight on red-pepper in vivo pot test.