• Journal of Microbiology and Biotechnology
• /
• v.18 no.5
• /
• pp.908-912
• /
• 2008

To achieve a higher succinic acid productivity and evaluate the industrial applicability, this study used Mannheimia succiniciproducens LPK7 (knock-out: ldhA, pflB, pta-ackA), which was recently designed to enhance the productivity of succinic acid and reduce by-product secretion. Anaerobic continuous fermentation of Mannheimia succiniciproducens LPK7 was carried out at different glucose feed concentrations and dilution rates. After extensive fermentation experiments, a succinic acid yield and productivity of 0.38 mol/mol and 1.77 g/l/h, respectively, were achieved with a glucose feed concentration of 18.0 g/l and $0.2\;h^{-1}$ dilution rate. A similar amount of succinic acid production was also produced in batch culture experiments. Therefore, these optimal conditions can be industrially applied for the continuous production of succinic acid. To examine the quantitative balance of the metabolism, a flux distribution analysis was also performed using the metabolic network model of glycolysis and the pentose phosphate pathway.

• Journal of Microbiology and Biotechnology
• /
• v.26 no.7
• /
• pp.1234-1241
• /
• 2016

Methanol is a versatile compound that can be biologically synthesized from methane (CH₄) by methanotrophs using a low energy-consuming and environment-friendly process. Methylocella tundrae is a type II methanotroph that can utilize CH₄ as a carbon and energy source. Methanol is produced in the first step of the metabolic pathway of methanotrophs and is further oxidized into formaldehyde. Several parameters must be optimized to achieve high methanol production. In this study, we optimized the production conditions and process parameters for methanol production. The optimum incubation time, substrate, pH, agitation rate, temperature, phosphate buffer and sodium formate concentration, and cell concentration were determined to be 24 h, 50% CH₄, pH 7, 150 rpm, 30℃, 100 mM and 50 mM, and 18 mg/ml, respectively. The optimization of these parameters significantly improved methanol production from 0.66 to 5.18 mM. The use of alginate-encapsulated cells resulted in enhanced methanol production stability and reusability of cells after five cycles of reuse under batch culture conditions.

• Horticultural Science & Technology
• /
• v.30 no.2
• /
• pp.107-122
• /
• 2012

In plants, color is a powerful tool to attract insects and herbivores which act as pollinators and vehicles of seed dispersion. In particular, flower color has held key post for human with aesthetic value. Horticultural industry has developed methods to produce new and attractive color varieties in flowering plants. Carotenoids are one of the main pigments being responsible for red, orange, and yellow colors. Their biosynthetic pathway has been considered as a major target of metabolic engineering for color modification of flowers and fruits. Here, we review the diverse efforts to modify pigment phenotype by the control of carotenogenic gene expression and enzyme levels. Recent reports about regulating degradation and storage of carotenoids will be also summarized to help the creation of engineered flower with novel color phenotype which is not existed in nature.

• Plant Biotechnology Reports
• /
• v.4 no.4
• /
• pp.269-280
• /
• 2010

Lilium ${\times}$ formolongi was genetically engineered by Agrobacterium-mediated transformation with the plasmid pCrtZW-N8idi-crtEBIY, which contains seven enzyme genes under the regulation of the CaMV 35S promoter. In the transformants, ketocarotenoids were detected in both calli and leaves, which showed a strong orange color. In transgenic calli, the total amount of carotenoids [133.3 ${\mu}g/g$ fresh weight (FW)] was 26.1-fold higher than in wild-type calli. The chlorophyll content and photosynthetic efficiency in transgenic orange plantlets were significantly lowered; however, after several months of subculture, they had turned into plantlets with green leaves that showed significant increases in chlorophyll and photosynthetic efficiency. The total carotenoid contents in leaves of transgenic orange and green plantlets were quantified at 102.9 and 135.2 ${\mu}g/g$ FW, respectively, corresponding to 5.6- and 7.4-fold increases over the levels in the wild-type. Ketocarotenoids such as echinenone, canthaxanthin, 3'-hydroxyechinenone, 3-hydroxyechinenone, and astaxanthin were detected in both transgenic calli and orange leaves. A significant change in the type and composition of ketocarotenoids was observed during the transition from orange transgenic plantlets to green plantlets. Although 3'-hydroxyechinenone, 3-hydroxyechinenone, astaxanthin, and adonirubin were absent, and echinenone and canthaxanthin were present at lower levels, interestingly, the upregulation of carotenoid biosynthesis led to an increase in the total carotenoid concentration (+31.4%) in leaves of the transgenic green plantlets.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.15 no.4
• /
• pp.425-430
• /
• 2005

Many problems can be formulated in terms nf graphs and thus solved by graph-theoretic algorithms. This paper is concerned with finding paths between nodes over the distributed and overlapped graphs. The proposed method allows multiple agents to cooperate to find paths without merging the distributed graphs. For each graph there is a designated agent which is charged of providing path-finding service for hot graph and initiating the path-finding tasks of which path starts from the graph. The proposed method earlier on constructs an abstract graph so-called viewgraph for the distributed overlapped graphs and thus enables to extract the information about how to guide the path finding over the graphs. The viewgraph is shared by all agents which determine how to coordinate other agents for the purpose of finding paths. Each agent maintains the shortest path information among the nodes which are placed in different overlapped subgraphs of her graph. Once an agent is asked to get a path from a node on her graph to another node on another's graph, she directs other agents to provide the necessary information for finding paths.

• Journal of Plant Biotechnology
• /
• v.37 no.4
• /
• pp.388-393
• /
• 2010

Recently, a number of successful research reports are accumulated to increase the carotenoid level in potato tuber such as $\beta$-carotene, precursor of vitamin A and keto-carotenoid like astaxanthin in which is not synthesized in most plants tissue since it does not contain a specific enzyme to add keto-ring in carotenoid molecule. In particular, keto-carotenoids are more interested due to their strong antioxidant activity. Currently, the content of $\beta$-carotene was increased up to 3,600-fold ($47\;{\mu}g/g$ dry weight) when compared to the control potato tuber, parental cultivar for genetic modification. In addition, astaxanthin, one of the major keto-carotenoid was accumulated up to $14\;{\mu}g/g$ dry weight in potato tuber with red color by over expressing the gene encoding $\beta$-carotene ketolase isolated from marine microorganisms. In this article, we summarized carotenogenesis-related genes that have been used for metabolic engineering of carotenoid biosynthetic pathway in potato. Furthermore, strategies for the accumulation of carotenoids and ketocarotenoids in specific potato tuber, bottle necks, and future works are discussed.

• Journal of Microbiology and Biotechnology
• /
• v.29 no.6
• /
• pp.923-932
• /
• 2019

Current strategies of strain improvement processes are mainly focused on enhancing the synthetic pathways of the products. However, excessive metabolic flux often creates metabolic imbalances, which lead to growth retardation and ultimately limit the yield of the product. To solve this problem, we applied a dynamic regulation strategy to produce $\text\tiny{L}$-phenylalanine ($\text\tiny{L}$-Phe) in Escherichia coli. First, we constructed a series of Phe-induced promoters that exhibited different strengths through modification of the promoter region of tyrP. Then, two engineered promoters were separately introduced into a Phe-producing strain xllp1 to dynamically control the expression level of one pathway enzyme AroK. Batch fermentation results of the strain xllp3 showed that the titer of Phe reached 61.3 g/l at 48 h, representing a titer of 1.36-fold of the strain xllp1 (45.0 g/l). Moreover, the $\text\tiny{L}$-Phe yields on glucose of xllp3 (0.22 g/g) were also greatly improved, with an increase of 1.22-fold in comparison with the xllp1 (0.18 g/g). In summary, we successfully improved the titer of Phe by using dynamic regulation of one key enzyme and this strategy can be applied for improving the performance of strains producing other aromatic amino acids and derived compounds.

• Journal of Biomedical Engineering Research
• /
• v.32 no.1
• /
• pp.55-60
• /
• 2011

Although sound intensity is considered as one of important factors in auditory processing, its neural mechanism in auditory neurons with limited dynamic range of firing rates is still unclear. In this study, we examined the effect of sound intensity adaptation on the change of glucose metabolism in a rat brain using [F-18] micro positron emission tomography (PET) neuroimaging technique. In the experiment, broadband white noise sound was given for 30 minutes after the [F-18]FDG injection in order to explore the functional adaptation of rat brain into the sound intensity levels. Nine rats were scanned with four different sound intensity levels: 40 dB, 60 dB, 80 dB, 100 dB sound pressure level (SPL) for four weeks. When glucose uptake during the adaptation of a high intensity sound level (100 dB SPL) was compared with that during adaptation to a low intensity level (40 dB SPL) in the experiment, the former induced a greater uptake at bilateral cochlear nucleus, superior olivary complexes and inferior colliculi in the auditory pathway. Expectedly, the metabolic activity in those areas linearly increased as the sound intensity level increased. In contrast, significant decrease interestingly occurred in the bilateral auditory cortices: The activities of auditory cortex proportionally decreased with higher sound intensities. It may reflect that the auditory cortex actively down-regulates neural activities when the sound gets louder.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.45 no.4
• /
• pp.19-26
• /
• 2008

Gene set enrichment analysis (GSEA) is a computational method to identify statistically significant gene sets showing significant differences between two groups of microarray expression profiles and simultaneously uncover their biological meanings in an elegant way by employing gene annotation databases, such as Cytogenetic Band, KEGG pathways, gene ontology, and etc. For the gone set enrichment analysis, all the genes in a given dataset are first ordered by the signal-to-noise ratio between the groups and then further analyses are proceeded. Despite of its impressive results in several previous studies, however, gene ranking by the signal-to-noise ratio makes it difficult to consider highly up-regulated genes and highly down-regulated genes at the same time as the candidates of significant genes, which possibly reflect certain situations incurred in metabolic and signaling pathways. To deal with this problem, in this article, we investigate the gene set enrichment analysis method with Fisher criterion for gene ranking and also evaluate its effects in Leukemia related pathway analyses.

• Journal of Microbiology and Biotechnology
• /
• v.15 no.4
• /
• pp.880-886
• /
• 2005

Using carotenoid genes of Erwinia herbicola, metabolic engineering was carried out for lycopene production with the pAC-LYCO4 plasmid, which was composed of a chromosomal DNA fragment of E. herbicola containing the crtE, crtB, and crtI genes under the control of the tetracycline promoter and the ipi gene of Haematococcus pluvialis with the trc promoter. Plasmid pAC-LYCm4 was constructed for efficient expression of the four exogenous genes using a strong RBS sequence and the same tetracycline promoter. The optimized expression construct of pAC-LYCm4 increased Iycopene production three times as compared with pAC-LYCO4. pAC-LYCm5 containing ispA behind the four exogenous genes was constructed. There was no significant difference in Iycopene production and cell growth between pAC-LYCm4 and pAC-LYCm5. FPP synthase encoded by ispA was not rate-limiting for Iycopene production. Each gene of crtE, crtB, crtI, and ipi was overexpressed, using pBAD-crtE, pBAD-crtIB, and pBAD-ipiHPI, in addition to their expression from pAC-LYCm4. However, there was no increase oflycopene production with the additional overexpression of each exogenous gene. The four exogenous genes appeared to be not rate-limiting in cells harboring pAC-LYCm4. When pDdxs, pBAD24 containing dxs, was introduced into cells harboring lycopene synthetic plasmids, lycopene production of pAC-LYCO4, pAC-LYCm4, and pAC-LYCm5 was increased by 4.7-, 2.2-, and 2.2-fold, respectively. Lycopene production of pBAD-DXm4 containing crtE, crtB, crtI, ipi, and dxs was 5.2 mg/g dry cell weight with $0.2\%$ arabinose, which was 8.7-fold higher than that of the initial strain with pAC-LYC04. Therefore, the present study showed that proper regulation of a metabolically engineered pathway is important for Iycopene production.