• Journal of Microbiology and Biotechnology
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• v.12 no.2
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• pp.249-257
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• 2002

Pseudomonas fluorescens GL20 is a plant growth-promoting rhizobacterium that produces a large amount of hydroxamate siderophore under iron-limited conditions. The strain GL20 considerably inhibited the spore germination and hyphal growth of a plant pathogenic fungus, Fusarium solani, when iron was limited, significantly suppressed the root-rot disease on beans caused by F. solani, and enhanced the plant growth. The mechanism for the beneficial effect of strain GL20 on the disease suppression was due to the siderophore production, evidenced by mutant strains derived from the strain. Analysis of the outer membrane protein profile revealed that the growth of strain GL20 induced the synthesis of specific iron-regulated outer membrane proteins with molecular masses of 85- and 90 kDa as the high-affinity receptors for the ferric siderophore. In addition, a cross-feeding assay revealed the presence of multiple inducible receptors for heterologous siderophores in the strain. In order to induce increased efficacy and potential in biological control of plant disease, a siderophore-overproducing mutant, GL20-S207, was prepared by NTG mutagenesis. The mutant GL20-S207 produced nearly 2.3 times more siderophore than the parent strain. In pot trials of beans with F. solani, the mutant increased plant growth up to 1.5 times compared with that of the parent strain. These results suggest that the plant growth-promoting P. fluorescens GL20 and the genetically bred P. fluorescens GL20-S207 can play an important role in the biological control of soil-borne plant diseases in the rhizosphere.

• Animal Bioscience
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• v.34 no.3_spc
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• pp.345-353
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• 2021

Phytobiotics, also known as phytochemicals or phytogenics, have a wide variety of biological activities and have recently emerged as alternatives to synthetic antibiotic growth promoters. Numerous studies have reported the growth-promoting effects of phytobiotics in chickens, but their precise mechanism of action is yet to be elucidated. Phytobiotics are traditionally known for their antioxidant activity. However, extensive investigations have shown that these compounds also have anti-inflammatory, antimicrobial, and transcription-modulating effects. Phytobiotics are non-nutritive constituents, and their bioavailability is low. Nonetheless, their beneficial effects have been observed in several tissues or organs. The health benefits of the ingestion of phytobiotics are attributed to their antioxidant activity. However, several studies have revealed that not all these benefits could be explained by the antioxidant effects alone. In this review, I focused on the bioavailability of phytobiotics and the possible mechanisms underlying their overall effects on intestinal barrier functions, inflammatory status, gut microbiota, systemic inflammation, and metabolism, rather than the specific effects of each compound. I also discuss the possible mechanisms by which phytobiotics contribute to growth promotion in chickens.

• Journal of Plant Biotechnology
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• v.43 no.4
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• pp.405-410
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• 2016

Auxins are essential in plant growth and development. The auxin-stimulated elongation of plant cells has been explained by the "acid-growth theory", which was proposed forty years ago. According to this theory, the auxin activates plasma membrane $H^+-ATPase$ to induce proton extrusion into the apoplast, promoting cell expansion through the activation of cell wall-loosening proteins such as expansins. Even though accepted as the classical theory of auxin-induced cell growth for decades, the major signaling components comprising this model were unknown, until publication of recent reports. The major gap in the acid growth theory is the signaling mechanism by which auxin activates the plasma membrane $H^+-ATPase$. Recent genetic, molecular, and biochemical approaches reveal that several auxin-related molecules, such as TIR1/AFB AUX/IAA coreceptors and SMALL AUXIN UP RNA (SAUR), serve as important components of the acid-growth model, phosphorylating and subsequently activating the plasma membrane $H^+-ATPase$. These researches reestablish the four-decade-old theory by providing us the detailed signaling mechanism of auxininduced cell growth. In this review, we discuss the recent research progress in auxin-induced cell elongation, and a set of possible future works based on the reestablished acid-growth model.

• 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.16 no.4
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• pp.531-537
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• 2006

Lactic acid-producing bacteria (LABs) are known to have various beneficial properties for health. However, they are generally considered to have an adverse effect on teeth, since they produce acid. Nonetheless, milk and cheese containing specific LAB strains were recently found to have an inhibitory effect on dental caries in children, with an inhibitory activity towards the growth of Streptococcus mutans suggested as the responsible mechanism. Accordingly, the current study selected a probiotic candidate for oral health and studied its inhibitory mechanism against dental caries. Twenty-two LAB species belonging to eleven genuses were screened for promoting bone nodule formation using direct microscopic examination. Only one isolate, Weissella kimchii strain PL9001, increased the bone nodule formation significantly. The addition of W. kimchii strain PL9001 to bone cells prepared from mouse calvaria increased the bone nodule formation, calcium accumulation, and activity of alkaline phosphatase (the osteoblastic marker). Moreover, W. kimchii strain PL9001 inhibited the invasion of Streptococcus mutans into bone cells, and an organic extract of the culture supernatant of W. kimchii strain PL9001 inhibited the growth of Strep. mutans. Therefore, the results suggest that W. kimchii strain PL9001 can be used as a preventive measure against dental caries. This is the first time that a LAB has been shown to promote bone nodule formation and prevent the invasion of Strep. mutans into bone cells.

• 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.

• Journal of Microbiology and Biotechnology
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• v.19 no.10
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• pp.1250-1258
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• 2009

Bacillus spp., as a type of plant growth-promoting rhizobacteria (PGPR), were studied with regards promoting plant growth and inducing plant systemic resistance. The results of greenhouse experiments with tobacco plants demonstrated that treatment with the Bacillus spp. significantly enhanced the plant height and fresh weight, while clearly lowering the disease severity rating of the tobacco mosaic virus (TMV) at 28 days post-inoculation (dpi). The TMV accumulation in the young non-inoculated leaves was remarkably lower for all the plants treated with the Bacillus spp. An RT-PCR analysis of the signaling regulatory genes Coil and NPR1, and defense genes PR-1a and PR-1b, in the tobacco treated with the Bacillus spp. revealed an association with enhancing the systemic resistance of tobacco to TMV. A further analysis of two expansin genes that regulate plant cell growth, NtEXP2 and NtEXP6, also verified a concomitant growth promotion in the roots and leaves of the tobacco responding to the Bacillus spp.

• Mycobiology
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• v.29 no.1
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• pp.48-53
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• 2001

Plants have the ability to acquire an enhanced level of resistance to pathogen attack after being exposed to specific biotic stimuli. To obtain plant growth-promoting rhizobacteria inducing resistance against cucumber anthracnose by Colletotrichum orbiculare, more than 800 strains of rhizobacteria were screened in the greenhouse. Among these strains, Bacillus amyloliquefaciens solate EXTN-1 showed significant disease control efficacy on the plants. Induction of pathogenesis-related(PR-la) gene expression by EXTN-1 was assessed using tobacco plants transformed with PR-1a::$\beta$-glucuronidase(GUS) construct. GUS activities of tobacco treated with EXTN-1 and salicylic acid-treated transgenic tobacco were significantly higher than those of tobacco plants with other treatments. Gene expression analyses indicated that EXTN-1 induces the accumulation of defense-related genes of tobacco. The results showed that some defense genes are expressed by the treatment with EXTN-1 suggesting the similar resistance mechanism by salicylic acid.

• Journal of Microbiology and Biotechnology
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• v.33 no.9
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• pp.1119-1129
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• 2023

Seeds are colonized by diverse microorganisms that can improve the growth and stress resistance of host plants. Although understanding the mechanisms of plant endophyte-host plant interactions is increasing, much of this knowledge does not come from seed endophytes, particularly under environmental stress that the plant host grows to face, including biotic (e.g., pathogens, herbivores and insects) and abiotic factors (e.g., drought, heavy metals and salt). In this article, we first provided a framework for the assembly and function of seed endophytes and discussed the sources and assembly process of seed endophytes. Following that, we reviewed the impact of environmental factors on the assembly of seed endophytes. Lastly, we explored recent advances in the growth promotion and stress resistance enhancement of plants, functioning by seed endophytes under various biotic and abiotic stressors.

• The Plant Pathology Journal
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• v.17 no.3
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• pp.174-179
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• 2001

The plant growth-promoting Pseudomonas strains, WR8-3 (Pseudomonas fluorescens), WR9-11 (Pseudomonas sp.) and WR9-16 (P.putida), which induced resistance systematically in watermelon to gummy stem rot were investigated on their induced systemic resistance(ISR)-related characteristics. The pyoverdine production was repressed in the standard succinate medium by increasing the concentration of $\textrm{FeCL}_3$. But the iron-binding ability on chrome azurol S agar media (CAS) was observed only in the strains, WR8-3 and WR9-16. When the two strains were mutated, the resulting iron-binding siderophore-negative mutants, WR8-3m and WR 9-16m, failed to promote the growth of watermelon and to induce resistance. The strains, WR8-3 and WR 9-16, slightly inhibited the growth of Didymella bryoniae at a low concentration of $\textrm{FeCL}_3$ on Kong's medium B, but not to exert control dffect. The strain WR9-11 showed antagonism in the concentration of $\textrm{FeCL}_3$ from 0 to $1,000\mu\textrm{M}$. When the crude lipoplysaccharide of each strain was treated in the rhizosphere of watermelon, mean lesion area was similar to that of the untreated control. The strains, WR9-11 and WR9-16 produced some level of hydrogen cyanide (HCN). Salicylic acid production was not detected in all of the strains.