• Korean Journal of Soil Science and Fertilizer
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• v.20 no.2
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• pp.179-183
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• 1987

A series of laboratory experiments were conducted to find out the populations and identification of soil bacteria, fungi and their B/F ratio in the rhizosphere of intensively cultivatad hot-pepper, garlic, flower plants, chinese cabbage, and round onion. The results obtained are summarized as follows: 1. The number of bacteria, fungi and their B/F ratio are remarkably lower than that of normal paddy soils. 2. Nitrate reducers and bacteria which utilized simple sugars for their sole carbon source are predominated in the rhizosphere of intensively cultivated upland crops. 3. Alkaligenetic bacteria predominate in rhizosphere of garlic and tomato cultivated upland soils. 4. Genera of Pseudomonas, Xanthomonas, Bacillus, Arthrobacter, and Achromobacterium are the most common species in the rhizosphere of intensively cultivated upland crops and flower plants. 5. Phytotoxin producers such as Stachybotris sp. were identified in all rhizospheres of intensively cultivated upland crops and flower plants. 6. Most common and highest population of soil fungi were obtained for the genera of Penicillium, Humicola, Phoma and Aspergillus in the rhizosphere of intensively cultivated upland crops and flower plants.

• Korean Journal of Microbiology
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• v.51 no.4
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• pp.347-354
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• 2015

Soybean is well known to be originated from Korea and far-east Asian countries, and studies of many root nodule bacteria associated with soybean have mainly-focused on nitrogen fixation, but much less study was carried out on bacterial community in the rhizosphere of soybean. In this study, we analyzed the bacterial community in rhizosphere of Korean soybean, Daepungkong using the pyrosequencing method based on the 16S rRNA gene to characterize the change of the rhizosphere community structure according to the growth stages of soybeans and to elucidate bacterial core community in rhizosphere of soybean. Our results revealed that bacterial community of rhizosphere soil differed from that of bulk soil and was composed of a total of 21 bacterial phyla. The predominant phylum in the rhizosphere of soybean was Proteobacteria (36.6-42.5%) and followed by Acidobacteria (8.6-9.4%), Bacteroidetes (6.1-10.9%), Actinobacteria (6.4-9.8%), and Firmicutes (5.7-6.3%). The bacterial core community in soybean rhizosphere was mainly composed of the operational taxonomic units (OTUs) belonging to the phylum Proteobacteria throughout all growth stages. The OTU00006 belonged to the genus Bradyrhizobium had the highest abundance and Steroidobacter, Streptomyces, Devosia were followed. These results show that bacterial core community in soybean rhizosphere was mainly composed of OTUs associated with plant growth promotion and nutrient cycles.

• The Plant Pathology Journal
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• v.37 no.6
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• pp.662-672
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• 2021

Plant growth-promoting bacteria improve plant growth under abiotic stress conditions. However, their effects on microbial succession in the rhizosphere are poorly understood. In this study, the inoculants of Bacillus mesonae strain H20-5 were administered to tomato plants grown in soils with different salinity levels (EC of 2, 4, and 6 dS/m). The bacterial communities in the bulk and rhizosphere soils were examined 14 days after H20-5 treatment using Illumina MiSeq sequencing of the bacterial 16S rRNA gene. Although the abundance of H20-5 rapidly decreased in the bulk and rhizosphere soils, a shift in the bacterial community was observed following H20-5 treatment. The variation in bacterial communities due to H20-5 treatment was higher in the rhizosphere than in the bulk soils. Additionally, the bacterial species richness and diversity were greater in the H20-5 treated rhizosphere than in the control. The composition and structure of the bacterial communities varied with soil salinity levels, and those in the H20-5 treated rhizosphere soil were clustered. The members of Actinobacteria genera, including Kineosporia, Virgisporangium, Actinoplanes, Gaiella, Blastococcus, and Solirubrobacter, were enriched in the H20-5 treated rhizosphere soils. The microbial co-occurrence network of the bacterial community in the H20-5 treated rhizosphere soils had more modules and keystone taxa compared to the control. These findings revealed that the strain H20-5 induced systemic tolerance in tomato plants and influenced the diversity, composition, structure, and network of bacterial communities. The bacterial community in the H20-5 treated rhizosphere soils also appeared to be relatively stable to soil salinity changes.

• International Journal of Industrial Entomology and Biomaterials
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• v.35 no.2
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• pp.63-70
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• 2017

Native fluorescent pseudomonas bacteria were isolated from rhizosphere soil of mulberry and were evaluated against powdery mildew. In vitro conidial germination study showed significant (P<0.05) variation in conidial germination by bacterial strains Pf1 and Pf3. Mildew incidence was significantly varied due to treatment with various pseudomonas strains in vivo. Significantly (P<0.05) less mildew incidence was in plants treated with the bacterial strain Pf1 (9.11%) followed by Pf3 (13.48%) controlling 69.40% and 54.75% respectively compared with untreated control. Similarly, mildew severity was least (8.51%) in plants treated with strain Pf1 followed by Pf5 (9.23%) and Pf3 (9.72%) controlling the severity by 84.51%, 77.01% and 71.96% respectively compared with control. The bacterial strains significantly influenced biochemical constituents such as chlorophyll, protein and soluble sugar content of the mulberry leaf. Similarly, bacterial strains significantly increased the activity of the peroxidase (PO) and Polyphenol oxydase (PPO) activity from $7^{th}$ day up to the $28^{th}$ day after treatment. The strain Pf1, Pf3 and Pf5 exhibited a marked enhancement in the peroxidase at different periods of infection. Significant (P<0.01) negative correlation was found between powdery mildew severity with phenol content ($R^2=0.67$) as well as peroxidase ($R^2=0.92$) and polyphenol oxidase ($R^2=0.72$) activity thus confirms induction of systemic resistance in mulberry by pseudomonas bacteria. The study shows scope for exploration of rhizosphere fluorescent pseudomonas bacteria for induction of systemic resistance in mulberry to contain powdery mildew disease effectively.

• Journal of Microbiology and Biotechnology
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• v.22 no.6
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• pp.763-770
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• 2012

Pseudomonas fluorescens 2112, isolated in Korea as an indigenous antagonistic bacteria, can produce 2,4-diacetylphloroglucinol (2,4-DAPG) and the siderophore pyoveridin2112 for the control of phytophthora blight of red-pepper. P. fluorescens 2112 was classified into a new genotype C among the 17 genotypes of 2,4-DAPG producers, by phlD restriction fragment length polymorphism (RFLP). The colonizing ability of P. fluorescens 2112 in pea rhizosphere was equal to the well-known pea colonizers, P. fluorescens Q8r1 (genotype D) and MVP1-4 (genotype P), after 6 cycling cultivations for 18 weeks. Four tested 2,4-DAPG-producing Pseudomonas spp. could colonize with about a 96% dominance ratio against total bacteria in pea rhizosphere. The strain P. fluorescens 2112 was as good a colonizer as other Pseudomonas spp. genotypes in pea plant growth-promoting rhizobacteria.

• Microbiology and Biotechnology Letters
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• v.34 no.1
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• pp.78-82
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• 2006

Since there could be more and rather various diazotrophs in rhizosphere of wild crops than those in rhizosphere of cultivars, some wild gramineous crops grown in Korea were collected for isolating nitrogen-fixing bacteria. Six diazotrophs were purified from their roots using nitrogen-free media. The isolated bacteria were partially identified as 4 genera by 16S rDNA sequence analysis: Stenotrophomonas sp., Bosea sp., Klebsiella sp., and Azorhizobium sp. By PCR amplification and sequence analysis, DNA fragments extracted from all isolates turned out to have an individual nifH homologous gene. Five isolates (KNUC163, KNUC165, KNUC169, KNUC170, and KNUC171) showed auxin activity and four isolates (KNUC163, KNUC166, KNUC170, and KNUC171) produced siderophores. Especially,3 strains of S. maltophilia showed both auxin and siderophore activities. In conclusion, the isolated nitrogen-fixing bacteria might have capabilities for plant growth promotion.

• Korean Journal of Microbiology
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• v.49 no.3
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• pp.297-300
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• 2013

EPS producing bacteria were enumerated in ginseng root system (rhizosphere soil, rhizoplane, inside of root). EPS producing bacterial density of rhizosphere soil, rhizoplane and inside of root were distributed $9.0{\times}10^6$ CFU/g, $7.0{\times}10^6$ CFU/g, and $1.4{\times}10^3$ CFU/g, respectively. Phylogenetic analysis of the 24 EPS producing isolates based on the 16S rRNA gene sequences, EPS producing isolates from rhizosphere soil (RS) belong to genus Arthrobacter (6 strains) and Rhizobium (1 strain). EPS producing bacteria from rhizoplane (RP) were Arthrobacter (6 strains), Rhodococcus (1 strain) and Pseudomonas (1 strain). EPS producing bacteria from inside of root (IR) were categorized into Rhzobium (6 strains), Bacillus (1 strain), Rhodococcus (1 strain), and Pseudomonas (1 strain). Phylogenetic analysis indicated that Arthrobacter may be a member of representative EPS producing bacteria from ginseng rhizosphere soil and rhizoplane, and Rhizobium is typical EPS producing isolates from inside of ginseng root. The yield of EPS was 10.0 and 4.9 g/L by Rhizobium sp. 1NP2 (KACC 17637) and Arthrobacter sp. 5MP1 (KACC 17636). The purified EPS were analyzed by Bio-LC and glucose, galactose, mannose and glucosamine were detected. The major EPS sugar of these strains was glucose (72.7-84.9%).

• Journal of Ginseng Research
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• v.40 no.2
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• pp.97-104
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• 2016

Background: Rhizobacteria play an important role in plant defense and could be promising sources of biocontrol agents. This study aimed to screen antagonistic bacteria and develop a biocontrol system for root rot complex of Panax notoginseng. Methods: Pure-culture methods were used to isolate bacteria from the rhizosphere soil of notoginseng plants. The identification of isolates was based on the analysis of 16S ribosomal RNA (rRNA) sequences. Results: A total of 279 bacteria were obtained from rhizosphere soils of healthy and root-rot notoginseng plants, and uncultivated soil. Among all the isolates, 88 showed antagonistic activity to at least one of three phytopathogenic fungi, Fusarium oxysporum, Fusarium solani, and Phoma herbarum mainly causing root rot disease of P. notoginseng. Based on the 16S rRNA sequencing, the antagonistic bacteria were characterized into four clusters, Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetesi. The genus Bacillus was the most frequently isolated, and Bacillus siamensis (Hs02), Bacillus atrophaeus (Hs09) showed strong antagonistic activity to the three pathogens. The distribution pattern differed in soil types, genera Achromobacter, Acidovorax, Brevibacterium, Brevundimonas, Flavimonas, and Streptomyces were only found in rhizosphere of healthy plants, while Delftia, Leclercia, Brevibacillus, Microbacterium, Pantoea, Rhizobium, and Stenotrophomonas only exist in soil of diseased plant, and Acinetobacter only exist in uncultivated soil. Conclusion: The results suggest that diverse bacteria exist in the P. notoginseng rhizosphere soil, with differences in community in the same field, and antagonistic isolates may be good potential biological control agent for the notoginseng root-rot diseases caused by F. oxysporum, Fusarium solani, and Panax herbarum.

• The Plant Pathology Journal
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• v.27 no.3
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• pp.242-248
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• 2011

Several soil bacteria were found to degrade N-Acylhomoserine lactones (NAHLs), thereby interfering with the bacterial quorum sensing system. In this research, fifteen strains of NAHL degrading rhizobacteria were isolated from potato rhizosphere. Based on phenotypic characteristics and 16S rDNA sequence analyses, the strains were identified as members of genera Bacillus, Streptomyces, Arthrobacter, Pseudomonas and Mesorhizobium. All tested isolates were capable to degrade both synthetic and natural NAHL produced by Pectobacterium carotovorum subsp. carotovorum (Pcc) strain EMPCC. In quorum quenching experiments selected isolates, especially Mesorhizobium sp., were markedly reduced the pathogenicity of Pcc strain EMPCC in potato tubers and totally suppressed tissue maceration on potato tubers. These led to consider the latter as a useful biocontrol agent against Pectobacterium spp.

• Microbiology and Biotechnology Letters
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• v.33 no.3
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• pp.169-177
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• 2005

This study focuses on investigating roles of microorganisms in decontamination of reed rhizosphere in Sunchon Bay, Korea, which is considered one of the marsh and mud environment severely affected by human activities such as agriculture and fisheries. In general, the bay is known to play the role of the buffering zone to reduce the sudden impact or change by environmental stresses. In our initial efforts to elucidate the microbial functions in decontamination process in reed rhizosphere, pure bacteria capable of degrading aromatic hydrocarbons were isolated from reed (Phragmites communis) rhizosphere of Sunchon bay by enrichment culture using either benzene, toluene, ethylbenzene, or xylene (BTEX) as a sole source of carbon and energy. Measurement of the rates of BTEX degradation and cell growth during the incubation in BTEX media under several temperature conditions demonstrated maximized degradation of BTEX at $37^{\circ}C$ in both strains. Both strains were also resistant to all the heavy metals and antibiotics tested in this study, as well as they grew well at $42^{\circ}C$. Identification of the isolates based on 16S rRNA gene sequences, and a variety of phenotypic and morphologic properties revealed that the two strains capable of BTEX catabolism were among Microbacterium sp., and Rhodococcus sp. with over $95{\%}$ confidence, designated Microbacterium sp. EMB-1 and Rhodococcus sp. EMB-2, respectively This result suggested that in the rhizosphere of reed, one of major salt marsh plants they might play an important roles in decontamination process of reed rhizosphere contaminated with petroleum such as BTEX.