• 한국생물공학회:학술대회논문집
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• 2005.04a
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• pp.152-156
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• 2005

In this study, we tried to optimize the composition of medium and culture conditions for the total avermectin and avermectin B1 production from S. avermitilis, which is a natural producer of avermectin family. Among various carbon and organic nitrogen sources tested, fructose and malt extract were most effective on avermectin production. Next addition of polyethylene glycol and $K_{2}HPO_{4}$ in medium significantly improved the intracellular contents of avermectin. Thus the optimized medium composition was 50 g/L fructose, 30 g/L malt extract, 5 g/L casamino acid, 2.5 g/L PEG 3,350, and 1 g/L $K_{2}HPO_{4}$, which increased the avermection production from10 to 478 mg/L. The contents of avermectin B1 complex was about 50% of the total amount of avermectin.

• The Korean Journal of Food And Nutrition
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• v.19 no.4
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• pp.496-501
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• 2006

This study was to isolate a bacterium producing a alkaline protease from mud flats of the west seaside of Korea and to investigate the biochemical analysis of the alkaline protease producing from the isolate. The isolate was named as Gelidibacter sp. HK-1 based on 16S rRNA sequence, Gram staining and the photograph of electron microsceope. Optimum temperature for growth and pretense production of the isolate was $25^{\circ}C$. Growth of the isolate was reached at stationary phase after 10hrs followed by inoculation. Maximum activity of protease produced from the isolate was shown after 14hrs. Optimum temperature and pH for the protease activity were $45^{\circ}C$ and pH 9, respectively. Molecular weight of the pretense was about 50KD and the partial amino acid sequence of the pretense was Ala-Try-Ala-Leu-Asn-Thr-Ser-Val-Thr-Glu-Thr-Phe-Ala-Lys. The partial amino acid sequences of the protease showed significant homology with a pretense produced from Streptomyces avermitilis.

• KSBB Journal
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• v.20 no.5 s.94
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• pp.376-382
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• 2005

Avermectin (AVM) $B_{1a}$ produced by Streptomyces avermitilis via polyketide pathway is a secondary metabolite with powerful anthelmintic and insecticidal activities, thus being used as an efficient agent in the field of agriculture and animal health. It has been reported that a precursor for AVM $B_{1a}$ biosynthesis was isoleucine and the biosynthetic pathway of AVM $B_{1a}$ was closely similar to that of fatty acid. Based on understanding of the biosynthetic pathway of AVM $B_{1a}$, we intended to screen various mutants resistant against O-methyl threonine (OMT), an isoleucine-anti metabolite, and/or mutants resistant against p-fluoro phenoxy acetic acid (pFAC), an inhibitor of fatty acid biosynthesis. It was inferred that these mutants could produce AVM $B_{1a}$ more efficiently, due to the acquired capability of not only overproducing isoleucine intracellularly but also channelling metabolized carbon-sources into the polyketide pathway, thus leading to enhanced biosynthesis of AVM $B_{1a}$. The resulting mutant (PFA-1 strain) resistant against 100 ppm of pFAC was able to produce approximately 42 fold higher amount of AVM $B_{1a}$ compared to the parallel mother strain (4,200 vs. 100 units/l). In addition, through the process of continuous strain improvement program carried out by gradually increasing the OMT concentration, it was possible to obtain a more attractive mutant with greater AVM $B_{1a}$ production capacity (9,000 units/l). Notable was that significantly higher producer (12,000 units/l) could be selected through further screening of the resistant mutants, this time, to even higher concentration of PFAC. Meanwhile, through the analysis of AVM Bla production histograms (i.e., number of strains according to their AVM $B_{1a}$ biosynthetic ability) for the earlier strains in comparison with the high producers having the characteristics of resistance to OMT and pFAC, it was found that production stability of the high-yielding producers were remarkably improved, as demonstrated by the fact that larger proportion of the mutated strains had greater capability of AVM $B_{1a}$ biosynthesis ($71\%$ in the range between 5,000 and 7,000 units/L; $47\%$ in the range between 6,000 and 7,000 units/l). Based on these consequences, it was concluded that the rational screening strategy based on the understanding of the biosynthetic pathway of AVM $B_{1a}$ was very effective in obtaining high-yielding mutants with the features of enhanced production stability.

• Korean Journal of Microbiology
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• v.40 no.3
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• pp.183-188
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• 2004

Stenotrophomonas sp. OK-5 capable of degrading TNT has been found to have three nitroreductase fractions designated as NTR fractions I, II, and III. NTR in a previous study. This study was attempted to reveal physiological and molecular characteristics of NTR fractions I, II, and III in strain OK-5. Several chemicals (e.g., EDTA, NaCl, dithiothreitol, $\beta$-mercaptoethanol) were tested for their effect on enzyme activity of NTRs, demonstrating that enzyme activities of NTR fractions I, II, and III from OK-5 were inhibited in the presence of $\beta$-mercaptoethanol. Substrate specificity test showed that NTR fractions I, II, and III all have over 70% enzyme activities for nitrobenzene or RDX as a substrate. N-terminal amino acid sequence of NTR fraction I from Stenotrophomonas sp. OK-5 was $^1MSDLLNADAVVQLFRTARDS^20$ and exhibited 70% sequence homology with that of NTR from Xanthomonas campestris. NTR I gene from Stenotrophomonas sp. OK-5 (SmOK5nrI) shared extensive sequence homology in deduced amino acid sequence of PCR product with NTRs from Xanthomonas campestris (81 %), X. axonopodis (75%), Streptomyces avermitilis(30%), whereas they had low homology with that from P. putida KT2440 (pnrB) (16%).