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Survivable Traffic Grooming in WDM Ring Networks
Sankaranarayanan, Srivatsan,Subramaniam, Suresh,Choi, Hong-Sik,Choi, Hyeong-Ah The Korea Institute of Information and Commucation 2007 Journal of communications and networks Vol.9 No.1
Traffic grooming, in which low-rate circuits are multiplexed onto wavelengths, with the goal of minimizing the number of add-drop multiplexers (ADMs) and wavelengths has received much research attention from the optical networking community in recent years. While previous work has considered various traffic models and network architectures, protection requirements of the circuits have not been considered. In this paper, we consider survivable traffic grooming, or grooming traffic which contains a mix of circuits that need protection and that do not need protection. We assume a unidirectional ring network with all-to-all symmetric traffic with $t\geq1$ circuits between each node pair, of which s require protection. As it turns out, survivable traffic grooming presents a significant tradeoff between the number of wavelengths and the number of ADMs, which is almost non-existent in non-survivable traffic grooming for this type of traffic. We explore this tradeoff for some specific cases in this paper. We also present some new results and solution methods for solving certain non-survivable traffic grooming problems.
Sankaranarayanan, M.,Seol, E.,Kim, Y.,Chauhan, A. S.,Park, S. SPRINGER 2017 Journal of industrial microbiology & biotechnology Vol.44 No.3
<P>Glycerol dehydratase (GDHt), which converts glycerol to 3-hydroxypropionaldehyde, is essential to the production of 1,3-propanediol (1,3-PDO) or 3-hydroxypropionic acid (3-HP). A reliable GDHt activity assay in crude-cell extract was developed. In the assay, GDHt converted 1,2-propanediol (1,2-PDO) to propionaldehyde, which was further converted to 1-propionic acid by aldehyde dehydrogenase (KGSADH) or to 1-propanol by yeast-alcohol dehydrogenase (yADH), while the NADH concentration change was monitored spectrophotometrically. Cells should be disintegrated by Bead Beater/French Press, not by chemical methods (BugBuster (R)/B-PER (TM)), because the reagents significantly inactivated GDHt and coupling enzymes. Furthermore, in the assay mixture, a much higher activity of KGSADH (> 200-fold) or yADH (> 400-fold) than that of GDHt should have been maintained. Under optimal conditions, both KGSADH and yADH showed practically the same activity. The coupled-enzyme assay method established here should prove to be applicable to recombinant strains developed for the production of 3-HP and/or 1,3-PDO from glycerol.</P>
Production of 3-hydroxypropionic acid from glycerol by acid tolerant Escherichia coli.
Sankaranarayanan, Mugesh,Ashok, Somasundar,Park, Sunghoon Published by Stockton Press on behalf of the Socie 2014 Journal of industrial microbiology & biotechnology Vol.41 No.7
<P>The biological production of 3-hydroxypropionic acid (3-HP) has attracted significant attention because of its industrial importance. The low titer, yield and productivity, all of which are related directly or indirectly to the toxicity of 3-HP, have limited the commercial production of 3-HP. The aim of this study was to identify and select a 3-HP tolerant Escherichia coli strain among nine strains reported to produce various organic acids efficiently at high titer. When transformed with heterologous glycerol dehydratase, reactivase and aldehyde dehydrogenase, all nine E. coli strains produced 3-HP from glycerol but the level of 3-HP production, protein expression and activities of the important enzymes differed significantly according to the strain. Two E. coli strains, W3110 and W, showed higher levels of growth than the others in the presence of 25?g/L 3-HP. In the glycerol fed-batch bioreactor experiments, the recombinant E. coli W produced a high level of 3-HP at 460??10?mM (41.5??1.1?g/L) in 48?h with a yield of 31?% and a productivity of 0.86??0.05?g/L h. In contrast, the recombinant E. coli W3110 produced only 180??8.5?mM 3-HP (15.3??0.8?g/L) in 48?h with a yield and productivity of 26?% and 0.36??0.02?g/L h, respectively. This shows that the tolerance to and the production of 3-HP differ significantly among the well-known, similar strains of E. coli. The titer and productivity obtained with E. coli W were the highest reported thus far for the biological production of 3-HP from glycerol by E. coli.</P>
Sankaranarayanan, Mugesh,Somasundar, Ashok,Seol, Eunhee,Chauhan, Ashish Singh,Kwon, Seongjin,Jung, Gyoo Yeol,Park, Sunghoon Elsevier Science Publishers 2017 Journal of biotechnology Vol.259 No.-
<P>Biological 3-hydroxypropionic acid (3-HP) production from glycerol is a two-step reaction catalyzed by glycerol dehydratase (GDHt) and aldehyde dehydrogenase (ALDH). Recombinant strains developed for 3-HP production often suffer from the accumulation of a toxic intermediate, 3-hydroxypropionaldehyde (3-HPA). In order to avoid 3-HPA accumulation, balancing of the two enzymatic activities, in the present study, was attempted by employment of synthetic-regulatory cassettes comprising varying-strength promoters and bicistronic ribosome binding sites (RBSs). When tested in recombinant Escherichia coli, the cassettes could precisely and differentially control the gene expression in transcription, protein expression and enzymatic activity. Five recombinant strains showing different expressions for GDHt were developed and studied for 3-HPA accumulation and 3-HP production. It was found that 3-HPA accumulation could be completely abolished when expressing ALDH at a level approximately 8-fold higher than that of GDHt. One of the strains, SP4, produced 625 mM (56.4 g/L) of 3-HP in a fed-batch bioreactor, though late-period production was limited by acetate accumulation. Overall, this study demonstrated the importance of pathway balancing in 3-HP production as well as the utility of the synthetic cassette architecture for precise control of bacterial gene expression.</P>