• Microbiology and Biotechnology Letters
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• v.21 no.3
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• pp.288-292
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• 1993

An agar medium(HY) was developed to detect the urease-producing lactic acid bacteria. HY medium was prepared with the addition of tryptone, glucose and tween 80 to the supernatant of autoclaved skim milk and yeast extract mixture. There was no difference in eumeration of lactic acid bacteria between the HY and commercial media, such as M17, MRS and BCP agar. The urease activity of Streptococcus salivarius subsp. thermophilus was detected on the HY agar medium contained urea by the color change of bromocresol purple as the pH indicator, but not on the commerical agar media. Furthermore, it was succeeded to screen the urease activity of bacteria in skim milk used as a raw material in dairy product manufacture. Therefore, HY medium was proved to be suitable for the screening of urease-producing lactic acid bacteria.

• Korean Journal Plant Pathology
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• v.14 no.6
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• pp.598-602
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• 1998

Twenty two rhizobacteria were isolated from the roots and rhizosphere of radish, carnation, potato and tomato. There isolates produced a fluorescent pigment in King's B medium and identified as Pseudomonas spp. These isolates colonized roots and rhizosphere of the host plants. In the study of cultural characteristics of the bacteria, the pH of the culture broth was changed from neutral (7.0) to alkali (8.8∼9.41) and the numbers of cells were increased from 106 to 108 after 40 hr of incubation in basal standard succinate medium. The salicylic acid production identified by pink color reaction were observed in 7 bacteria. Out of these 7 salicylic acid producing bacteria, only 2 strains of bacteria such as Pseudomonas fluorescens RS006, and Pseudomonas sp. EN401 were confirmed as salicylic acid producers by optical density measurement. Therefore, for screening of salicylic acid producing bacteria from the roots and rhizosphere, color reaction of the culture medium should be done in the first step, and then optical density measurement of culture extract should be made for the confirmation of salicylic acid production.

• Journal of Microbiology and Biotechnology
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• v.27 no.8
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• pp.1441-1448
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• 2017

Antibacterial compounds are widely used in the treatment of human and animal diseases. The overuse of antibiotics has led to a rapid rise in the prevalence of drug-resistant bacteria, making the development of new antibacterial compounds essential. This study focused on developing a fast and easy method for identifying marine bacteria that produce antibiotic compounds. Eight randomly selected marine target bacterial species (Agrococcus terreus, Bacillus algicola, Mesoflavibacter zeaxanthinifaciens, Pseudoalteromonas flavipulchra, P. peptidolytica, P. piscicida, P. rubra, and Zunongwangia atlantica) were tested for production of antibacterial compounds against four strains of test bacteria (B. cereus, B. subtilis, Halomonas smyrnensis, and Vibrio alginolyticus). Colony picking was used as the primary screening method. Clear zones were observed around colonies of P. flavipulchra, P. peptidolytica, P. piscicida, and P. rubra tested against B. cereus, B. subtilis, and H. smyrnensis. The efficiency of colony scraping and broth culture methods for antimicrobial compound extraction was also compared using a disk diffusion assay. P. peptidolytica, P. piscicida, and P. rubra showed antagonistic activity against H. smyrnensis, B. cereus, and B. subtilis, respectively, only in the colony scraping method. Our results show that colony picking and colony scraping are effective, quick, and easy methods of screening for antibacterial compound-producing bacteria.

• Journal of Microbiology and Biotechnology
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• v.10 no.3
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• pp.423-428
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• 2000

Bacteriocins are classified as proteins which are produced by heterogeneous groups of bacteria, having and antimicrobial effect of the closely related organisms. Recently, bacteriocins derived from lactic acid bacteria and other food-related organisms have been the subject of much research on potential food biopreservatives. The goal of this study was to screen and characterize the bacteriocinogenic lactic acid bacteria from Jeot-gal(commercial fermented fish foods). All bacteriocinogenic isolates were identified as lactic acid bacteria. Isolates NK24, NK34, and SA72 were tentatively identified as Lactobacillus brevis, according to the API 50 CHL kit database. All antimicrobial substances produced from four lactic acid bacteria isolates completely lost their antibacterial activity after being treated with some proteases, indicating to their proteinaceous nature. The bacteriocin produced from isolates NK24, NK34, and SA72 showed a broad spectrum of activity when compared to those produced from isolate SA131. All bacteriocins isolated during the course of this study showed a bactericidal mode of inhibition.

• YAKHAK HOEJI
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• v.47 no.3
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• pp.184-189
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• 2003

Peptide deformylase (PDF) is essential and unique to bacteria, thus making it an attractive target for the discovery of novel antibacterial drugs. PDF deformylates the N-formylmethionine of newly synthesized polypeptides in prokaryotes. In this study, a pdf gene from Staphylococcus aureus 6538p was cloned in pET-14b vector and PDF protein was over-produced in Escherichia coli BL21 (DE3). NH$_2$-terminal His-tagged PDF protein was purified by nickel-nitrilotriacetic acid (Ni-NTA) metal-affinity chromatography. Enzymatic activity of purified 6xHis-tagged PDF was tested on the substrate (formyl-Methionine-Alanine-Serine) by formate dehydrogenase-coupled spectrometric assay of peptide deformylase. For the discovery of new PDF inhibitors from chemical libraries and culture broths of soil bacteria, a target-oriented screening system using a 96-well plate was developed. About 3,000 commercial chemical libraries were tested in this screening system, and 2 chemicals (0.07％) among them showed an inhibitory activity against PDF enzyme. This result showed that a new screening system can be used for the discovery of new PDF inhibitors.

• Journal of Microbiology and Biotechnology
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• v.11 no.3
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• pp.491-496
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• 2001

A modification of decarboxylating agar medium as described by niven was performed to improve the detection method of biogenic amine-producing bacteria and to eliminate the false-positive. A total of 120 bacterial strains isolated from kimchi were used to evaluate different dicarboxylating agar media and for screening biogenic amines. Potential false-positives ranged from approximately 66 to 79% of the strains tested in the already well-known media. In our improved medium, none of the 120 strains showed the potential false-positives. There was a good agreement (81.7%-87.5%) between the results obtained by the improved medium and by HPLC analysis. Consequently, this medium was greatly improved in screening biogenic amine-producing bacteria and discarding false-positives. Of the 120 kimchi isolates, 14.2, 18.3, 37.5, and 0.8% were found by HPLC to be the producers of histamine, tyramine, putrescine (as a form of spermine), and cadaverine, respectively. The proportion of biogenic amine producer during kimchi fermentation increased to a maximum at an immature period and decreased thereafter.

• Mycobiology
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• v.28 no.4
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• pp.190-192
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• 2000

Antifungal bacteria for biological control of plant diseases or production of novel antibiotics to plant pathogens were isolated in 1997 from various soils of Ansung, Chunan, Koyang, and Paju in Korea. Sixty-four bacterial strains pre-screened from approximately 1,400 strains were tested on V-8 juice agar against eight plant pathogenic fungi using in vitro bioassay technique for inhibition of mycelial growth. Test pathogens were Alternaria mali, Colletotrichum gloeosporioides, C. orbiculare, Fusarium oxysporum f. sp. cucumerinum, F. oxysporum f. sp. lycopersici, Magnaporthe grisea, Phytophthora capsici, and Rhizoctonia solani. A wide range of antifungal activity of bacterial strains was found against the pathogenic fungi, and strain RC-B77 showed the best antifungal activity. Correlation analysis between inhibition of each fungus and mean inhibition of all eight fungi by 64 bacterial strains revealed that C. gloeosporioides would be best appropriate for detecting bacterial strains producing antibiotics with potential as biocontrol agents for plant pathogens.

• YAKHAK HOEJI
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• v.45 no.3
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• pp.245-250
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• 2001

Aminoacyl tRNA synthetases of bacteria are known as potential targets for new anti-microbial agents. To isolate new inhibitors of bacterial methionyl-tRNA synthetases from natural sources, a new target-oriented screening system using whole cells which are over-expressing a target enzyme was developed. Approximately 8,000 culture broths of microorganisms from soils were tested by this screening system. Among them, ten culture broths was found to contain inhibitory activity against methionyl -tRNA synthetases of Escherichia coli. For the validation of the screening system, this new method was compared with in vitro enzymatic method. Seven out of 10 culture broths showed inhibitory activity against methionyl-tRNA synthetases of E. coli. This result showed that the new screening system was comparable to the enzyme assay. Thus we believe that our screening system as a new method can be applied for the screening of new antibiotics inhibiting bacterial methionyl-tRNA synthetases from natural products.

• The Plant Pathology Journal
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• v.21 no.2
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• pp.93-98
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• 2005

Molecular ecological studies of microbial communities revealed that only tiny fraction of total microorganisms in nature have been identified and characterized, because the majority of them have not been cultivated. A concept, metagenome, represents the total microbial genome in natural ecosystem consisting of genomes from both culturable microorganisms and viable but non-culturable bacteria. The construction and screening of metagenomic libraries in culturable bacteria constitute a valuable resource for obtaining novel microbial genes and products. Several novel enzymes and antibiotics have been identified from the metagenomic approaches in many different microbial communities. Phenotypic analysis of the introduced unknown genes in culturable bacteria could be an important way for functional genomics of unculturable bacteria. However, estimation of the number of clones required to uncover the microbial diversity from various environments has been almost impossible due to the enormous microbial diversity and various microbial population structure. Massive construction of metagenomic libraries and development of high throughput screening technology should be necessary to obtain valuable microbial resources. This paper presents the recent progress in metagenomic studies including our results and potential of metagenomics in plant pathology and agriculture.

• KSBB Journal
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• v.14 no.2
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• pp.146-152
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• 1999

Screening experiments were carried out in order to select bacteria causing brown blotch disease on the mushroom, Pleurotus ostreatus. Four bacteria causing brown blotch disease were isolated from Pleurotus ostreatus and soils around the mushroom farm. Three strains showing antagonism against brown blotch causing bacteria, A-11, A-20 and A-29 were also isolated through methods pitting test, cross checking and biochemical test, and identified as Pseudomonas fluorescence for A-11 and A-20, and Pseudomonas sp. for A-29, respectively. Colonial morphology test also showed that A-11 and A-29 were appeared as transparent gel with green color, whereas the colony of A-20 showed opaque gel with light green color.