• The Plant Pathology Journal
• /
• v.24 no.4
• /
• pp.461-468
• /
• 2008

An endophytic bacterial strain YC5480 producing antifungal and phytotoxic compounds simultaneously was isolated from the surface sterilized root of Artemisia sp. collected at Jinju area, Korea. The bacterial strain was identified as a species of Pseudomonas brassicacearum based on its 16S rRNA gene sequence analysis and physiological and biochemical characteristics. The seed germination and growth of monocot and dicot plants were inhibited by culture filtrate (1/10-strength Tryptic Soy Broth) of the strain. The germination rate of radish seeds in the culture filtrate differed in various culture media. Only 20% of radish seeds germinated in the culture media of 1/2 TSB for 5 days incubation. Mycelial growth of fungal pathogens, Colletotrichum gloeosporioides, Fusarium oxysporum and Phytophthora capsici was also inhibited by the culture filtrate of the strain YC5480. An antifungal compound, KS-1 with slight inhibitory activity of radish seed germination at 1,000 ppm and a seed germination inhibitory compound, KS-2 without suppression of fungal growth were produced simultaneously in TSB. The compounds KS-1 and KS-2 were identified to be 2,4-diacetylphloroglucinol (DAPG) and 2,4,6-trihydroxyacetophenone (THA), respectively.

• The Plant Pathology Journal
• /
• v.38 no.4
• /
• pp.313-322
• /
• 2022

Seed-borne pathogens in crops reduce the seed germination rate and hamper seedling growth, leading to significant yield loss. Due to the growing concerns about environmental damage and the development of resistance to agrochemicals among pathogen populations, there is a strong demand for eco-friendly alternatives to synthetic chemicals in agriculture. It has been well established during the last few decades that plant seeds harbor diverse microbes, some of which are vertically transmitted and important for plant health and productivity. In this study, we isolated culturable endophytic bacteria and fungi from soybean seeds and evaluated their antagonistic activities against common bacterial and fungal seed-borne pathogens of soybean. A total of 87 bacterial isolates and 66 fungal isolates were obtained. Sequencing of 16S rDNA and internal transcribed spacer amplicon showed that these isolates correspond to 30 and 15 different species of bacteria and fungi, respectively. Our antibacterial and antifungal activity assay showed that four fungal species and nine bacterial species have the potential to suppress the growth of at least one seed-borne pathogen tested in the study. Among them, Pseudomonas koreensis appears to have strong antagonistic activities across all the pathogens. Our collection of soybean seed endophytes would be a valuable resource not only for studying biology and ecology of seed endophytes but also for practical deployment of seed endophytes toward crop protection.

• Proceedings of the Korean Society of Crop Science Conference
• /
• 2017.06a
• /
• pp.161-161
• /
• 2017

Seed endophytes are very remarkable groups of bacteria for their unique abilities of being vertically transmitted and conserved. As plants attain hybrid vigor and heterosis in the process of crossbreeding, this might also lead to the changes in the community structure and diversity of plant endophytes in the hybrid plants ultimately affecting the endophytes of the seeds. It would be interesting to characterize how seed endophyte composition change over time. The objective of this study is to gain insights into the influence of natural crossbreeding and parental lineage in the seed bacterial endophytic communities of two pure inbred lines exploring contributions of the two most important sources of plant endophytes - colonization from external sources and vertical transmission via seeds. Total genomic DNA was isolated from rice seeds and bacterial DNA was selectively amplified by PCR. The diversity of endophytic bacteria was studied through Terminal-Restriction Fragment Length Polymorphism (T-RFLP) analysis. Diversity between the original parents and the pure inbred line may show significant differences in terms of richness, evenness and diversity indices. Heat maps reveal astonishing contributions of both or either parents (IR29 ${\times}$ Pokkali and AT401 ${\times}$ IR31868) in the shaping of the bacterial seed endophytes of the hybrid, FL478 and IC32, respectively. Most of the T-RFs of the subsequent pure inbred line could be traced to any or both of the parents. Comparison of common and genotype-specific T-RFs of parents and their offspring reveals that majority of the T-RFs are shared suggesting higher transmission of bacterial communities common to both parents. The parents influence the bacterial community of their offspring. Unique T-RFs of the offspring also suggest external sources of colonization particularly as the seeds are cultivated in different ecogeographical locations. This study showed that host parental lines contributed greatly in the shaping of bacterial seed endophytes of their offspring. It also revealed transmission and potential conservation of core seed bacterial endophytes that generally become the dominant microbiota in the succeeding generations of plant hosts.

• Korean Journal of Microbiology
• /
• v.53 no.3
• /
• pp.193-199
• /
• 2017

This study was aimed to evaluate the antimicrobial activity of Penicillium purpurogenum ED76 on several clinically important microorganisms. The endophytic fungus P. purpurogenum ED76 was previously isolated from Swietenia macrophylla leaf. The antimicrobial efficacy of P. purpurogenum ED76 dichloromethane extract was determined via disc diffusion and broth microdilution assay. A kill curve study was conducted and the morphology of extract treated bacterial cells were viewed under scanning electron microscope. The dichloromethane extract showed significant inhibitory activity on 4 test bacteria and 2 test yeasts. The minimal inhibitory concentration of the extract ranged from 125 to $1,000{\mu}g/ml$, which indicates the different susceptibility levels of the test microorganisms to the fungal extract. The kill curve study has revealed a concentration-dependent inhibition for all test microorganisms. With the increase of the extract concentration, the microbial growth was significantly reduced. The scanning electron micrograph of dichloromethane extract-treated Staphylococcus aureus cells showed the total damage of the cells. The cell wall invagination of the bacterial cells also indicates the loss of cellular materials and metabolic activity. The gas chromatography mass spectrometry analysis of the extract also showed that the major compound was stigmasterol, which constitutes 45.30% of the total area. The dichloromethane extract of P. purpurogenum ED76 exhibited significant inhibitory activity on several clinically important bacteria and yeasts. The study proposed a possible mode of action that the extract cause significant damage to the morphology of S. aureus cells.

• Journal of Microbiology and Biotechnology
• /
• v.26 no.3
• /
• pp.488-492
• /
• 2016

Rhodococcus species have become increasingly important owing to their ability to degrade a wide range of toxic chemicals and produce bioactive compounds. Here, we report isolation of the Rhodococcus sp. KB6, which is a new leaf-inhabiting endophytic bacterium that suppresses black rot disease in sweet potato leaves. We determined the 7.0 Mb draft genome sequence of KB6 and have predicted 19 biosynthetic gene clusters for secondary metabolites, including heterobactins, which are a new class of siderophores. Notably, we showed the first internal colonization of host plants with Rhodococcus sp. KB6 and discuss its potential as a biocontrol agent for sustainable agriculture.

• Journal of Microbiology
• /
• v.45 no.1
• /
• pp.11-14
• /
• 2007

Over the last few years, the endophytic bacterial community associated with citrus has been studied as an important component interacting with Xylella fastidiosa, the causal agent of citrus variegated chlorosis(CVC). This bacterium may also colonize some model plants, such as Catharanthus roseus and Nicotiana clevelandii. In the present study, we compared the endophytic colonization of Citrus sinensis and Catharanthus rose us using the endophytic bacteria Klebsiella pneumoniae. We chose an appropriate strain, K. pneumoniae 342 (Kp342), labeled with the GFP gene. This strain was inoculated onto seedlings of C. sinensis and C. roseus. The isolation frequency was determined one week after the inoculation and the endophytic colonization of K. pneumoniae was observed using fluorescence microscopy. Although the endophytic bacterium was more frequently isolated from C. roseus than from C. sinensis, the colonization profiles for both host plants were similar, suggesting that C. roseus could be used as a model plant to study the interaction between endophytic bacteria and X. fastidiosa.

• Journal of Microbiology
• /
• v.45 no.5
• /
• pp.388-393
• /
• 2007

Citrus variegated chlorosis (CVC) is a disease of the sweet orange [Citrus sinensis (L.)], which is caused by Xylella fastidiosa subsp. pauca, a phytopathogenic bacterium that has been shown to infect all sweet orange cultivars. Sweet orange trees have been occasionally observed to be infected by Xylella fastidiosa without evidencing severe disease symptoms, whereas other trees in the same grove may exhibit severe disease symptoms. The principal endophytic bacterial species isolated from such CVC-asymptomatic citrus plants is Curtobacterium flaccumfaciens. The Madagascar periwinkle [Citrus sinensis (L.)] is a model plant which has been used to study X. fastidiosa in greenhouse environments. In order to characterize the interactions of X. fastidiosa and C. flaccumfaciens, periwinkle plants were inoculated separately with C. flaccumfaciens, X. fastidiosa, and both bacteria together. The number of flowers produced by the plants, the heights of the plants, and the exhibited disease symptoms were evaluated. PCR-primers for C. flaccumfaciens were designed in order to verify the presence of this endophytic bacterium in plant tissue, and to complement an existing assay for X. fastidiosa. These primers were capable of detecting C. flaccumfaciens in the periwinkle in the presence of X. fastidiosa. X. fastidiosa induced stunting and reduced the number of flowers produced by the periwinkle. When C. flaccumfaciens was inoculated together with X. fastidiosa, no stunting was observed. The number of flowers produced by our doubly- inoculated plants was an intermediate between the number produced by the plants inoculated with either of the bacteria separately. Our data indicate that C. flaccumfaciens interacted with X. fastidiosa in C. roseus, and reduced the severity of the disease symptoms induced by X. fastidiosa. Periwinkle is considered to be an excellent experimental system by which the interaction of C. flaccumfaciens and other endophytic bacteria with X. fastidiosa can be studied.

• Journal of agriculture & life science
• /
• v.50 no.1
• /
• pp.1-22
• /
• 2016

In this study, the securing state of nationally indicated beneficial microbial resources was evaluated in an aspect of bio-diversity using their taxonomical information. Depending on the analysis result with the Margalef's richness or the Mehinick's index which are representative bio-diversity analytical indices, species diversity values was revealed as 8.537, 3.546 within bacterial resources, 3.349, 2.167 within fungal resources. Several developed or researched beneficial strains and spoilage microbes showed relative taxonomical relationship with comparation of their biological information. As a result, we propose the necessity or countermeasure method for preventing the microbial spoilage with the overhauling consideration of advanced research on agricultural microbiology covering crop endophyte beneficial/spoilage microorganisms.

• The Korean Journal of Pesticide Science
• /
• v.18 no.4
• /
• pp.422-428
• /
• 2014

Endophytic bacterial strains from root tissue of strawberry were screened for their efficacy in growth improvement and control of Phytophthora blight disease of chili pepper plant under greenhouse condition. Plants treated with the strain EP103, identified as Pseudomonas fluorescens, showed growth improvement in terms of fresh weight and root length compared to the untreated control and other endophytic strains. When challenged with Phytophthora capsici, there was significant reduction of disease in EP103 treated plants with an efficacy of 78.7%. There was no direct inhibition of the target pathogen by EP103 when tested under in vitro antibiosis assay. Analysis of differential expression of selected marker genes for induced systemic resistance (ISR) in plants treated with EP103 and challenged with P. capsici showed up-regulation of PR1 and PR10 pathogenesis-related (PR) proteins. PCR analysis showed that EP103 produced secondary metabolites such as pyoluteorin, pyrrolnitrin, hydrogen cyanide and orfamide A. This study indicated the potential of endophytic P. fluorescens strain EP103 as an efficient biocontrol agent against P. capsici in chili pepper plant.

• Microbiology and Biotechnology Letters
• /
• v.35 no.1
• /
• pp.1-10
• /
• 2007

The 44 endophytic bacterial strains were isolated from surface-sterilized root of rice cultivated in seven different locations of Chungcheong province, Korea. Each isolate was introduced into rice seedlings grown gnotobiotically by inoculating scissor-cut first true leaf with cell suspensions, and the colonization capacity of each isolate in root tissue was analyzed at 7 days after inoculation. Sixteen out of 44 isolates were re-isolated from root successfully with the frequency of $10^{3-5}$ CFU/g tissue. Interestingly, seven out of 16 isolates were identified as Burkholderia species. The identity between inoculated strains and re-isolates was confirmed by genomic finger-printing and 16S rDNA sequence analysis. By a confocal laser scanning microscopic observation it was revealed that KJ001 strain, one of the sixteen isolates tagged with gfp colonized in root tissue especially around xylem. Six out of seven Burkholderia strains obtained in this study showed antagonizing activities against seven different fungal pathogens, contain nifH gene, and five of them enhanced growth of cucumber over 30%. The isolates showed no hypersensitive response on tobacco leaves and no pathogenecity in rice. From these results it was found that the endophytic Burkholderia strains will be useful in agriculture to develop a biocontrol agent or a bio-fertilizer.