• The Plant Pathology Journal
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• v.31 no.2
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• pp.165-175
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• 2015

Anthracnose is a fungal disease caused by Colletotrichum species that is detrimental to numerous plant species. Anthracnose control with fungicides has both human health and environmental safety implications. Despite increasing public concerns, fungicide use will continue in the absence of viable alternatives. There have been relatively less efforts to search antagonistic bacteria from mudflats harboring microbial diversity. A total of 420 bacterial strains were isolated from mudflats near the western sea of South Korea. Five bacterial strains, LB01, LB14, HM03, HM17, and LB15, were characterized as having antifungal properties in the presence of C. acutatum and C. gloeosporioides. The three Bacillus atrophaeus strains, LB14, HM03, and HM17, produced large quantities of chitinase and protease enzymes, whereas the B. amyloliquefaciens strain LB01 produced protease and cellulase enzymes. Two important antagonistic traits, siderophore production and solubilization of insoluble phosphate, were observed in the three B. atrophaeus strains. Analyses of disease suppression revealed that LB14 was most effective for suppressing the incidence of anthracnose symptoms on pepper fruits. LB14 produced antagonistic compounds and suppressed conidial germination of C. acutatum and C. gloeosporioides. The results from the present study will provide a basis for developing a reliable alternative to fungicides for anthracnose control.

• The Plant Pathology Journal
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• v.29 no.1
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• pp.67-76
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• 2013

A chitinolytic bacterial strain having strong antifungal activity was isolated and identified as Burkholderia cepacia MPC-7 based on 16S rRNA gene analysis. MPC-7 solubilized insoluble phosphorous in hydroxyapatite agar media. It produced gluconic acid and 2-keto-gluconic acid related to the decrease in pH of broth culture. The antagonist produced benzoic acid (BA) and phenylacetic acid (PA). The authentic compounds, BA and PA, showed a broad spectrum of antimicrobial activity against yeast, several bacterial and fungal pathogens in vitro. To demonstrate the biocontrol efficiency of MPC-7 on late blight disease caused by Phyto-phthora capsici, pepper plants in pot trials were treated with modified medium only (M), M plus zoospore inoculation (MP), MPC-7 cultured broth (B) and B plus zoospore inoculation (BP). With the sudden increase in root mortality, plants in MP wilted as early as five days after pathogen inoculation. However, plant in BP did not show any symptom of wilting until five days. Root mortality in BP was markedly reduced for as much as 50%. Plants in B had higher dry weight, P concentration in root, and larger leaf area compared to those in M and MP. These results suggested that B. cepacia MPC-7 should be considered as a candidate for the biological fertilizer as well as antimicrobial agent for pepper plants.

• The Korean Journal of Mycology
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• v.39 no.2
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• pp.126-130
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• 2011

In the course of search for multifunctional microbial inoculants, three Bacillus strains (BS11-1,BS11-2,BS11-3) with biological control and biofertilizing effects were selected. In this study, their ability for solubilization of insoluble phosphate, production of indole-3-acetic acid (IAA), siderophore, and hydrolytic enzymes, and antagonism against phytopathogenic fungi were estimated. All strains produced IAA and siderophore depending on culture time and produced a visible clear zone on agar plate containing 0.5% carboxylmethyl cellulose as a carbon source. Also, these strains exhibited antifungal activities against phytopathogenic fungi, Botrytis cinerea, Cylindrocarpon destructans, Fusarium oxysporum, Rhizoctonia solani, and Phytophthora capsici.

• Korean Journal of Microbiology
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• v.53 no.4
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• pp.351-353
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• 2017

Chryseobacterium sp. strain T16E-39, isolated from roots of a tomato plant, promotes plant growth and suppresses phytophthora blight and bacterial wilt diseases. The complete genome of strain T16E-39 consists of a circular chromosome with 4,872,888 base pairs with a G + C content of 35.22%. The genome includes 4,289 coding sequences, 15 rRNAs, and 71 tRNAs. We detected genes involved in phosphate solubilization, phytohormone regulation, antioxidant activity, chitin degradation, and the type IX secretion system (T9SS) that may be related to growth promotion and disease suppression in plants.

• Korean Journal of Microbiology
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• v.54 no.4
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• pp.471-473
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• 2018

Variovorax sp. PMC12 is a rhizobacterium isolated from tomato rhizosphere and enhanced the plant resistance to abiotic and biotic stresses. Here we present the complete genome sequence of strain PMC12. The genome is comprised of two circular chromosomes harboring 5,873,297 bp and 1,141,940 bp, respectively. A total of 6,436 protein-coding genes, 9 rRNAs, 64 tRNAs, 3 ncRNAs, and 80 pseudogenes were identified. We found genes involved in 1-aminocyclopropane-1-carboxylate (ACC) deaminase, antioxidant activity, phosphate solubilization, and biosynthesis of proline and siderophore. Those genes may be related to capability of improving plant resistance to various stresses including salinity, cold temperature, and phytopathogen.

• Microbiology and Biotechnology Letters
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• v.47 no.1
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• pp.105-115
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• 2019

Saline or alkaline condition in soil inhibits growth of most crop plants and limits crop yields in many parts of the world. Augmenting an alkaline soil with alkali-tolerant bacteria capable of promoting plant growth can be a promising approach in expanding fertile agricultural land. Near-shore environments of Dokdo Island, a remote island located in the middle of the East Sea, appear to have patches of seawater-influenced haloalkaline soil that is unsupportive for growth of conventional plants. To exploit metabolic capacities of alkali-tolerant bacteria for promoting plant growth in saline or alkaline soils, we isolated of alkali-tolerant bacteria from near-shore soil samples in Dokdo and investigated properties of the isolates. Alkali-tolerant bacteria were selectively cultivated by inoculating suspended and diluted soil samples on a plate medium adjusted to pH 10. Fifty colonies were identified based on their $GTG_5$-PCR genomic fingerprints and 16S rRNA gene sequences. Most isolates were affiliated to alkali-tolerant and/or halotolerant genera or species of the phyla Firmicutes (68%), Proteobacteria (30%) and Actinobacteria (2%). Unlike the typical soil bacterial flora in the island, alkali-tolerant isolates belonged to only certain taxa of terrestrial origin under the three phyla, which have traits of plant growth promoting activities including detoxification, phytohormone production, disease/pest control, nitrogen-fixation, phosphate solubilization or siderophore production. However, Firmicutes of marine origin generally dominated the alkali-tolerant community. Results of this study suggest that haloalkaline environments like Dokdo shore soils are important sources for plant growth promoting bacteria that can be employed in bio-augmentation of vegetation-poor alkaline soils.

• Journal of Microbiology and Biotechnology
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• v.29 no.1
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• pp.66-78
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• 2019

In this study, strain KNU17Pc1 was tested for its antifungal activity against Rhizoctonia solani AG-1(IA), which causes banded leaf and sheath blight (BLSB) of maize. KNU17Pc1 was tested further for its broad-spectrum antifungal activity and in vitro plant growth promoting (PGP) traits. In addition, the in vivo effects of KNU17Pc1 on reduction of BLSB severity and seedling growth promotion of two maize cultivars under greenhouse conditions were investigated. On the basis of multilocus sequence analysis (MLSA), KNU17Pc1 was confirmed as P. chlororaphis subsp. aurantiaca. The study revealed that KNU17Pc1 had strong in vitro antifungal activity and was effective toward all in vitro PGP traits except phosphate solubilization. In this study, for the first time, a strain of P. chlororaphis against Colletotrichum dematium, Colletotrichum gloeosporioides, Fusarium oxysporum f.sp. melonis, Fusarium subglutinans and Stemphylium lycopersici has been reported. Further biochemical studies showed that KNU17Pc1 was able to produce both types of phenazine derivatives, PCA and 2-OH-PCA. In addition, solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) analysis identified 13 volatile organic compounds (VOCs) in the TSB culture of KNU17Pc1, 1-undecene being the most abundant volatile. Moreover, for the first time, Octamethylcyclotetrasiloxan (D4), dimethyl disulfide, 2-methyl-1,3-butadiene and 1-undecene were detected in P. chlororaphis. Furthermore, this study reported for the first time the effectiveness of P. chlororaphis to control BLSB of maize. Hence, further studies are necessary to test the effectiveness of KNU17Pc1 under different environmental conditions so that it can be exploited further for biocontrol and plant growth promotion.

• Journal of Microbiology and Biotechnology
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• v.32 no.11
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• pp.1435-1446
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• 2022

Zinc-solubilizing bacteria can convert the insoluble form of zinc into soluble forms available to plants. This study was conducted to isolate and screen zinc-solubilizing actinobacteria from rhizosphere soils and to assess their effect on vegetable soybean growth. In total, 200 actinobacteria strains belonging to 10 genera were isolated from rhizosphere soil samples. Among these isolates, four showed zinc solubilization with solubilizing index values ranging from 3.11 to 3.78 on Bunt and Rovira agar supplemented with 0.1% zinc oxide. For the quantitative assay, in broth culture, strains CME34 and EX51 solubilized maximum available zinc contents of 529.71 and 243.58 ㎍/ml. Furthermore, indole-3-acetic acid (IAA) and ammonia were produced by these two strains, the strain CME34 produced the highest amount of IAA 4.62 ㎍/ml and the strain EX51 produced the highest amount of ammonia 361.04 ㎍/ml. In addition, the phosphate-solubilizing abilities in Pikovskaya's medium of CME34 and EX51 were 64.67 and 115.67 ㎍/ml. Based on morphological and biochemical characterization and 16S rDNA sequencing, the strains CME34 and EX51 were closely related to the genus Streptomyces. In a greenhouse experiment, single-strain inoculation of Streptomyces sp. CME34 or EX51 significantly increased the shoot length, root length, plant dry weight, number of pods per plant and number of seeds per plant of vegetable soybean plants compared to the uninoculated control. These findings facilitated the conclusion that the two Streptomyces strains have potential as zinc solubilizers and can be suggested as bioinoculants to promote the growth and yield of soybean.

• The Plant Pathology Journal
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• v.39 no.5
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• pp.430-448
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• 2023

Recently, strategies for controlling Fusarium oxysporum f. sp. lycopersici (Fol), the causal agent of Fusarium wilt of tomato, focus on using effective biocontrol agents. In this study, an analysis of the biocontrol and plant growth promoting (PGP) attributes of 11 isolates of loamy soil Bacillus spp. has been conducted. Among them, the isolates B.PNR1 and B.PNR2 inhibited the mycelial growth of Fol by inducing abnormal fungal cell wall structures and cell wall collapse. Moreover, broad-spectrum activity against four other plant pathogenic fungi, F. oxysporum f. sp. cubense race 1 (Foc), Sclerotium rolfsii, Colletotrichum musae, and C. gloeosporioides were noted for these isolates. These two Bacillus isolates produced indole acetic acid, phosphate solubilization enzymes, and amylolytic and cellulolytic enzymes. In the pot experiment, the culture filtrate from B.PNR1 showed greater inhibition of the fungal pathogens and significantly promoted the growth of tomato plants more than those of the other treatments. Isolate B.PNR1, the best biocontrol and PGP, was identified as Bacillus stercoris by its 16S rRNA gene sequence and whole genome sequencing analysis (WGS). The WGS, through genome mining, confirmed that the B.PNR1 genome contained genes/gene cluster of a nonribosomal peptide synthetase/polyketide synthase, such as fengycin, surfactin, bacillaene, subtilosin A, bacilysin, and bacillibactin, which are involved in antagonistic and PGP activities. Therefore, our finding demonstrates the effectiveness of B. stercoris strain B.PNR1 as an antagonist and for plant growth promotion, highlighting the use of this microorganism as a biocontrol agent against the Fusarium wilt pathogen and PGP abilities in tomatoes.