• 인터넷정보학회논문지
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• 제2권2호
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• pp.23-36
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• 2001

차별화 서비스(Differentiated Services) 망에서 실시간 멀티캐스트를 지원하기 위해서 EF(Expedite Forwarding) PHB(Per Hop Behavior)를 사용하여 전송한다면 EF PHB와 멀티캐스트 플로우의 특성 때문에 EF 멀티캐스트 플로우가 증가하게 될 경우 망의 관리나 자원 관리가 어렵다. 또한 LBE(Lower Than Best-effort) PHB를 이용한 멀티캐스트 전송은 전송지연을 보장할 수 없다는 단점이 있다. 이러한 문제를 해결하기 위하여 본 논문에서는 AF(Assured Forwarding) PHB를 이용하여, 허용 가능한 홉 당 지연시간 이내에서 처리를 해줄 수 있는 저지연 멀티캐스트(Low-delay Multicast)라는 새로운 PHB를 제안하고, 이를 위한 차별화 서비스 망에서의 핵심요소인 첫 흘 라우터. 내부 라우터. 경계 라우터들의 큐 구조를 설계하고 각 라우터들에서의 큐 관리 및 스케줄링 기법을 설계한다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제9권3호
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• pp.196-200
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• 2004

The supra molecular weight poly(〔R〕-3-hydroxybutyrate) (PH B), having a molecular weight greater than 2 million Da, has recently been found to possess improved mechanical properties compared with the normal molecular weight PHB, which has a molecular weight of less than 1 million Da. However, applications for this PHB have been hampered due to the difficulty of its production. Reported here, is the development of a new metabolically engineered Escherichia coli strain and its fermentation for high level production of supra molecular weight PHB. Recombinant E. coli strains, harboring plasm ids of different copy numbers containing the Alcaligenes latus PHB biosynthesis genes, were cultured and the molecular weights of the accumulated PHB were compared. When the recombinant E. coli XL1-Blue, harboring a medium-copy-number pJC2 containing the A. latus PHB biosynthesis genes, was cultivated by fed-batch culture at pH 6.0, supra molecular weight PHB could be produced at up to 89.8 g/L with a productivity of 2.07 g PHB/L-h. The molecular weight of PHB obtained under these conditions was as high as 22 MDa, exceeding by an order of magnitude the molecular weight of PHB typically produced in Ralstonia eutropha or recombinant E. coli.

• KSBB Journal
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• 제10권2호
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• pp.176-182
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• 1995

Methylobacterium organophilum을 이용하여 다당류(메틸란)와 poly-${\beta}$-hydroxybutyrate(PHB)의 생산에 영향을 주는 환경 및 생리적 인자들을 조사하였다. PHB 축적을 위하여는 $38^{\circ}C$, 다당류의 생산을 위하여는 $30^{\circ}C$가 최적이었다. pH의 경우는 P PHB의 축적은 pH 7 ~ 8, 다당류의 생산은 pH 6~7 이 최적이였다. 질소원 제한 상태하에서의 $Mo^{2+}, Mg^{2+} 또는 Mn^{2+}$ 등의 결핍조건에셔는 질소원만의 제한조건보다 P PHB 축적은 증가하였으나, 다당류 생산은 감소하였 다. 질소원의 제한없이 $K^+$만의 결핍조건에서는 균 체증식도 억제되었고 다당류도 생성되지 않았지만 건조균체당 PHB 함량은 60%까지 증가하였다. PHB와 다당류의 동시 생산을 위한 C/N 비율의 효 는 C/N 비율이 높을수록 질소원의 제한효과 때문에 균체증식은 감소되었지만 건조균체량당 PHB 함량과 다당류의 생성은 현저히 증가하였다.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2001년도 추계학술발표대회
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• pp.731-734
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• 2001

An efficient fermentation strategy for the high level production of ultra-high-molecular weight poly(3-hdyroxybutyrate) (PHB) was developed. Although the cell and PHA concentrations obtained by flask cultures at different initial pH (6.0 or 6.9) were almost same level, the molecular mass of PHB produced were quite different along with the initial pH. When a recombinant Escherichia coli XL1-Blue harboring pJC2 containing the Alcaligenes latus PHB biosynthesis genes was cultivated in flask culture (pH 6.0), the PHB having a very high molecular weight of 22 MDa could be produced while only below 1 MDa at initial pH 6.9. The ultra-high-molecular weight PHB could be synthesized to high concentration of 89.8 g/L resulting in the PHB productivity of 2.07 g/L-h by simple fed-batch culture. In this study, we report that PHB having various molecular mass can be produced by employing metabolically engineered E. coli strains harboring the plasmids of different copy numbers containing the A. latus phbCAB genes.

• Journal of Microbiology and Biotechnology
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• 제13권3호
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• pp.477-481
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• 2003

The community escape response of Rhodobacter sphaeroides is exerted through the action of CerR and CerI, which code for a LuxR-type regulatory protein and acylhomoserine lactone synthase, respectively. Deletion of chromosomal DNA including cerR and cerI (mutant RI) or insertional interruption of cert (mutant AP3) resulted in two-fold increase in the cellular poly-${\beta}$-hydroxybutyrate (PHB) content In comparison with the wild-type under aerobic growth conditions. The PHB synthase (PhbC) activities of the cer mutants were doubled, and the enzyme expression was regulated at the level of phbC transcription. Thus, CerR, possibly in response to autoinducer (AI), appears to modulate the PHB content of aerobically grown cells by downregulating phbC transcription.

• 한국미생물·생명공학회지
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• 제21권3호
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• pp.221-228
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• 1993

In order to achieve poly-beta-hydroxybutyric acid (PHB) production using recombinant DNA in various host bacterial cells, the isolation of genes for PHB biosynthesis was attempted. As a result, a 5.2kb DNA fragment containing phbCAB operon of Alcaligenes eutrophus was isolated by colony hybridization using synthetic oligodeoxyribonucleotides as probes. The constructed recmbinant plasmid pSK(+)-phbCAB operon was transferred to Escherichia coli, and the obtained transformant accumulated considerable amount of PHB.

• Journal of Microbiology and Biotechnology
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• 제10권5호
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• pp.628-631
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• 2000

The timing of poly(3-Hydroxybutyrate) (PHB) biosynthesis was controlled by varying the agitation speed of a stirred tank fermentor during the pH-stat fed-batch culture of recombinant Escherichia coli strain GCSC 6576 harboring pSYL107. Using a concentrated whey solution containing ca. 200 g/l lactose as the nutrient feed, the PHB content was only 57% after 35h due to volumetric limitation of the fermentor. However, by limiting the oxygen by maintaining the agitation speed at 300 rpm, the final PHB content increased to 70% after 70h with a cell concentration of 15 g/l. When the agitation speed was increased up to 500 rpm, a cell concentration of 31 g/l with 80% PHB was obtained after 52h. A further increase in the maximum agitation speed increased the cell concentration, PHB concentration, and PHB productivity, however, the PHB content decreased to 56-58%.

• 미생물학회지
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• 제36권4호
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• pp.299-305
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• 2000

생분해성 플라스틱으로 현재 상업화에 가장 근접해 있는 poly-3-hydroxybutyrate (PHB), $Sky-Green^R$(SG) 및 $Mater-Bi^R$(MB)를 활성오니토 및 경작토에 매립하여 PHB 분해세균 3주, SG 분해세균 3주 및 MB 분해세균 1주를 분리하였다. PHB 분해세균은 Flavimonas oryzihabitans, Corynebacterium pseudodiphtheriticum 및 Micrococcus diversus로, SG 분해세균은 Pseudomonas vesicuraris, Pasteurlla multocida 및 Flavobacterium odoratum으로, MB 분해세균은 Pseudomonas vesicuraris로 동정되었다. 각 플라스틱 film을 함유한 무기염 액체배지에서 28일 간의 생분해성 실험 결과 평균 중량감소는 PHB와 SG은 각각 44~69% 및 25~32%, MB는 29%를 나타내어 PHB의 생분해성이 가장 우수하였다. 각 플라스틱 film의 활성오니토 매립 전과 후의 표면 변화를 조사한 결과 미생물이 다공성의 film 표면에 많은 colony를 형성하는 것이 SEM으로 관찰되었다. PHB, SG 및 MB의 무생물적 분해와 F. oryzihabitans에 의한 미생물학적 생분해를 TOC와 pH 변화로 측정하여 비교 분석하였을 때, SG과 MB는 분해 정도가 서로 유사하였으나 PHB는 SG는 MB에 비하여 dir 3배 더 빠르게 무생물적 분해가 일어났다. Yeast extract를 포함한 배지에서 PHB, GS 및 MB의 분해는 yeast extract를 포함하지 않은 배지에서 보다 훨씬 빠르게 안정되었으며, 두 경우 모두 PHB의 분해는 SG 및 MB에 비하여 더 빠르게 일어졌다.

• 한국미생물·생명공학회지
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• 제18권3호
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• pp.273-279
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• 1990

PHB 생산을 위하여 메탄올을 기질로 한 선별배지에서 토양, 하천수, 퇴비 등으로부터 분홍색 색소를 가지는 PHB 축적 facultative methylotroph를 분리하여, 균주의 특성을 검토하였다. 분리균주의 최적 생육조건과 PHB 축적을 위한 배양조건을 조사한 결과 균체의 생육은 메탄올 농도 1.0(v/v), 질소원인$ NH_4C$ 농도 1.0g/l, 즉 C/N ratio 13.2 일때 그리고 pH 7.0과'$30^{\circ}C$에서 가장 좋았으며, PHB는 C/N ratio가 50.8, 즉 메탄올 농도 1.0(v/v )$NH_4CL$ 0.26g/l 일때, 그리고 pH 6.0일 때 건조중량의 약 40까지 축적되었다. 고농도 메탄올에 의한 생육저해를 극복하기 위하여 기질을 간헐적으로 계속 공급해주는 fed-batch 배양을 시도한 결과 균체량은 14g/l, PHB 축척량은 5.5g/l까지 증가시킬 수 있었다. 생산된 PHB를 분리.정제하여 IR과 $^I H-NMR$로 구조를 분석한 결과 3-hydroxybutyric acid 의 homopolymer임이 확인되었다. 또한 균주의 pink-pigment를 추출하여 absorption spectrum를 조사하여 그 특성을 규명하였다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제7권5호
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• pp.281-288
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• 2002

Recombinant Escherichia coli strain harboring the ${\lambda}$pR-pL promotor and heterologus poly-${\beta}$-hydroxybutyrate (PHB) biosynthesis genes was used to investigate the effect of culture conditions on the efficient PHB production. The expression of phb genes was induced by a temperature upshift from $33^{\circ}C\;to\;38^{\circ}C$. The protein expression levels were measured by using two-dimensional electrophoresis, and the enzyme activities were also measured to understand the effect of culture temperature, carbon sources, and the dissolved oxygen (DO) concentration on the metabolic regulations. AcetylCoA is an important branch point for PHB production. The decrease in DO concentration lowers the citrate synthase activity, thus limit the flux toward the TCA cycle, and increase the flux for PHB production. Since NADPH is required for PHB production, the PHB production does not continue leading the overproduction of acetate and lac-tate. Based on these observations, a new operation was considered where DO concentration was changed periodically, and it was verified its usefulness for the efficient PHB production by experiments.