• Journal of Life Science
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• v.23 no.8
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• pp.1010-1018
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• 2013

The greenhouse whitefly, Bemisia tabaci, is considered one of the most destructive pests of crops. In this study, we aimed to determine the optimal liquid culture conditions in shake flasks for maximal sporulation of Beauveria bassiana M130 using rice bran. The optimal initial pH for the spore production of B. bassiana using extracted rice bran medium was 5.2 and $28^{\circ}C$. The screening in shake flasks of carbon and nitrogen sources resulted in the identification of an optimal medium based on 0.5% $(NH_4)_2SO_4$, with extracted rice bran 8:1. Using this medium, a production level of $2.15{\times}10^9$ spores per ml was obtained after six days from culture inoculation at $28^{\circ}C$ in a rotary shaking incubator at 130 rpm. In addition, the specific activities of extracellular enzymes of chitinase and protease were $4,296{\mu}mol$ and $375{\mu}mol$, respectively. These results suggest that Beauveria bassiana M130 could be a bio-controller for the greenhouse whitefly.

• Journal of Life Science
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• v.20 no.3
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• pp.403-410
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• 2010

In order to produce high-quality fermenting composts, a microorganism was isolated from the natural world. The bacterium has not only in high enzyme activities but also had good antimicrobial activities against phytopathogenic microorganisms. Its cultivating characteristics were then investigated. Bacterium KJ-9, which contains high CMCase, protease and chitinase activities and excellent antimicrobial activities against phytopathogenic microorganisms, was separated from leaf mold and identified as Bacillus licheniformis by two methods: Bergey's Manual of Systematic Bacteriology and API 50 CHL Carbohydrate Test Kit (Bio Merieux, France) using an ATB (Automated Identification) computer system (Bio Merieux, France). Optimal medium for cultivation of B. licheniformis was 2% soluble starch as a carbon source, 0.5% yeast extract as a nitrogen source and 0.05% $MgSO_4{\cdot}7H_2O$. Optimal growth conditions of pH, temperature and shake speed were pH 7.0, $50^{\circ}C$ and 180 rpm, respectively. Culture broth of B. licheniformis KJ-9 cultured for 36~60 hr was effective in fungicidal activities against plant pathogens including Botrytis cinerea, Corynespora cassicola, Fusarium oxysporum, and Rhizoctonia solani.

• Korean Journal of Microbiology
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• v.55 no.3
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• pp.226-233
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• 2019

Ochratoxin A (OTA) that is one of mycotoxins produced mainly by Aspergillus spp. is a common contaminant of stored grains and poses health hazards to human and livestock. The aim of this study is to explore the ability of isolated bacteria Bacillus subtilis AF13 and Streptomyces shenzhenensis YR226 to inhibit growth and OTA production of 3 ochratoxigenic Aspergillus strains. The antifungal activity against mycelial growth and sporulation of Aspergillus strains was examined by coculture with AF13 and YR226 on potato dextrose agar plate. AF13 and YR226 reduced 77.58 and 78.48% of fungal colony radius, respectively, and both strains inhibited fungal sporulation up to 99% in 10 days of incubation. YR226 also reduced more than 91% of spore germination of 3 fungal strains. When Aspergillus strains were cocultured with AF13 or YR226 in yeast extract sucrose medium, mycelial growth and OTA production decreased in all three fungal strains. In particular, AF13 completely inhibited the mycelial growth of A. alutaceus and inhibited its OTA production by 99%, and YR226 also reduced mycelial growth and toxin production up to 99%, respectively. Antimicrobial substances produced by AF13 and YR226 included siderophore, chitinase, protease, ${\beta}$-1,3-glucanase and biosurfactant. These results suggest that AF13 and YR226 can be used in a biological method to prevent valuable crops against mycotoxigenic fungi, and therefore decrease economic damage in agriculture and feed industry.

• 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.

• Mycobiology
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• v.40 no.2
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• pp.111-116
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• 2012

Ten strains of the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana were evaluated to find the most effective strain for optimization studies. The first criterion tested for strain selection was the mortality (> 50%) of Spodoptera litura larvae after inoculation of the fungus for 4 days. Results on several bioassays revealed that B. bassiana BNBCRC showed the most virulence on mortality S. litura larvae (80% mortality). B. bassiana BNBCRC also showed the highest germination rate (72.22%). However, its conidia yield ($7.2{\times}10^8$ conidia/mL) was lower than those of B. bassiana B 14841 ($8.3{\times}10^8$ conidia/mL) and M. anisopliae M6 ($8.2{\times}10^8$ conidia/mL). The highest accumulative radial growth was obtained from the strain B14841 (37.10 mm/day) while the strain BNBCRC showed moderate radial growth (24.40 mm/day). M. anisopliae M6 possessed the highest protease activity (145.00 mU/mL) while M. anisopliae M8 possessed the highest chitinase activity (20.00 mU/mL) during 96~144 hr cultivation. Amongst these criteria, selection based on virulence and germination rate lead to the selection of B. bassiana BNBCRC. B. bassiana B14841 would be selected if based on growth rate while M. anisopliae M6 and M8 possessed the highest enzyme activities.

• The Plant Pathology Journal
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• v.31 no.3
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• pp.278-289
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• 2015

Indigenous strains of Trichoderma species isolated from rhizosphere soils of Tea gardens of Assam, north eastern state of India were assessed for in vitro antagonism against two important tea fungal pathogens namely Pestalotia theae and Fusarium solani. A potent antagonist against both tea pathogenic fungi, designated as SDRLIN1, was selected and identified as Trichoderma viride. The strain also showed substantial antifungal activity against five standard phytopathogenic fungi. Culture filtrate collected from stationary growth phase of the antagonist demonstrated a significantly higher degree of inhibitory activity against all the test fungi, demonstrating the presence of an optimal blend of extracellular antifungal metabolites. Moreover, quantitative enzyme assay of exponential and stationary culture filtrates revealed that the activity of cellulase, ${\beta}$-1,3-glucanase, pectinase, and amylase was highest in the exponential phase, whereas the activity of proteases and chitinase was noted highest in the stationary phase. Morphological changes such as hyphal swelling and distortion were also observed in the fungal pathogen grown on potato dextrose agar containing stationary phase culture filtrate. Moreover, the antifungal activity of the filtrate was significantly reduced but not entirely after heat or proteinase K treatment, demonstrating substantial role of certain unknown thermostable antifungal compound(s) in the inhibitory activity.

• Journal of Plant Biotechnology
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• v.44 no.2
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• pp.156-163
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• 2017

A greenhouse experiment was conducted for evaluation of ecological effects of transgenic melon plants in the rhizospheric soil in terms of soil properties, enzyme activities and microbial communities. Organic matter content of soil under transgenic melon plants was significantly higher than that of soil with non-transgenic melon plants. Significant variations were observed in organic matter, total P and K in soil cultivation with transgenic melon plants. There were also significant variations in the total numbers of colony forming units of fungi, actinomycetes and bacteria between soils treated with transgenic and non-transgenic melon plants. Transgenic and non-transgenic melon significantly enhanced several enzymes activities including urease, acid phosphatase, alkalin phosphatase, arysulphtase, ${\beta}$ glucosidase, dehydrogenase, protease and catalase. Soil polyphenoloxidase activity of $T_1$ transgenic melon was lower than that of $T_0$ transgenic melon and a non-melon plant during the same period. The first generation transgenic melon plants ($T_0$) showed significantly greater (p<0.05) effect on the activitiy of arylsulfatase, which increased from $2.540{\times}10^6CFU\;g^{-1}$ (control) to $19.860{\times}10^6CFU\;g^{-1}$ ($T_0$). These results clearly indicated that transgenic melon might change microbial communities, enzyme activities and soil chemical properties.

• The Plant Pathology Journal
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• v.28 no.3
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• pp.282-289
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• 2012

The root rot of pepper (Capsicum annuum L.) caused by Phytophthora capsici is one of the most important diseases affecting this crop worldwide. This work presents the evaluation of the capacity of Streptomyces griseus H7602 to protect pepper plants against Phytophthora capsici and establishes its role as a biocontrol agent. In this study, we isolated an actinomycete strain H7602 from rhizosphere soil, identified it as Streptomyces griseus by 16S rRNA analysis and demonstrated its antifungal activity against various plant pathogens including P. capsici. H7602 produced lytic emzymes such as chitinase, ${\beta}$-1,3-glucanase, lipase and protease. In addition, crude extract from H7602 also exhibited destructive activity toward P. capsici hyphae. In the pot trial, results showed the protective effect of H7602 against pepper from P. capsici. Application of H7602 culture suspension reduced 47.35% of root mortality and enhanced growth of pepper plants for 56.37% in fresh root and 17.56% g in fresh shoot as compared to control, resulting in greater protection to pepper plants against P. capsici infestation. Additionally, the enzymatic activities, chitinase and ${\beta}$-1,3-glucanase, were higher in rhizosphere soil and roots of pepper plants treated with H7602 than other treated plants. Therefore, our results indicated a clear potential of S. griseus H7602 to be used for biocontrol of root rot disease caused by P. capsici in pepper.

• Journal of Environmental Science International
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• v.22 no.11
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• pp.1457-1464
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• 2013

We investigated the optimal conditions for keratinase production by feather-degrading Pseudomonas geniculata H10 using one variable at a time (OVT) method. The optimal medium composition and cultural condition for keratinase production were determined to be glucose 0.15% (w/v), beef extract 0.08% (w/v), $KH_2PO_4$ 0.12% (w/v), $K_2HPO_4$ 0.02% (w/v), NaCl 0.07% (w/v), $MgSO_4{\cdot}7H_2O$ 0.03%, $MgCl_2{\cdot}6H_2O$ 0.04% along with initial pH 10 at 200 rpm and $25^{\circ}C$, respectively. The production yield of keratinase was 31.6 U/ml in an optimal condition, showing 4.6-fold higher than that in basal medium. The strain H10 also showed plant growth promoting activities. This strain had ammonification activity and produced indoleacetic acid (IAA), siderophore and a variety of hydrolytic enzymes such as protease, lipase and chitinase. Therefore, this study showed that P. geniculata H10 could be not only used to upgrade the nutritional value of feather wastes but also useful in situ biodegradation of feather wastes. Moreover, it is also a potential candidate for the development of biofertilizing agent applicable to crop plant soil.

• The Plant Pathology Journal
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• v.33 no.2
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• pp.170-183
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• 2017

Bacterial fruit blotch (BFB), which is caused by Acidovorax citrulli, is a serious threat to watermelon growers around the world. The present study was conducted to screen effective rhizobacterial isolates against 35 different A. citrulli isolates and determine their efficacy on BFB and growth parameters of watermelon. Two rhizobacterial isolates viz. Paenibacillus polymyxa (SN-22), Sinomonas atrocyanea (NSB-27) showed high inhibitory activity in the preliminary screening and were further evaluated for their effect on BFB and growth parameters of three different watermelon varieties under greenhouse conditions. The greenhouse experiment result revealed that SN-22 and NSB-27 significantly reduced BFB and had significant stimulatory effect on total chlorophyll content, plant height, total fresh weight and total dry weight compared to uninoculated plants across the tested three watermelon varieties. Analysis of the 16S ribosomal RNA (rRNA) sequences revealed that strains SN-22 belong to P. polymyxa and NSB-27 to S. atrocyanea with the bootstrap value of 99% and 98%, respectively. The isolates SN-22 and NSB-27 were tested for antagonistic and PGP traits. The result showed that the tested isolates produced siderophore, hydrolytic enzymes (protease and cellulose), chitinase, starch hydrolytic enzymes and they showed phosphate as well as zinc solubilizing capacity. This is the first report of P. polymyxa (SN-22) and S. atrocyanea (NSB-27) as biocontrol-plant growth promoting rhizobacteria on watermelon.