Heteronuclear molecules in an optical lattice: Theory and experiment

We study properties of two different atoms at a single optical lattice site at a heteronuclear atomic Feshbach resonance. We calculate the energy spectrum, the efficiency of rf association and the lifetime as a function of magnetic field and compare the results with the experimental data obtained for K-40 and Rb-87 [C. Ospelkaus et al., Phys. Rev. Lett. 97, 120402 (2006)]. We treat the interaction in terms of a regularized delta function pseudopotential and consider the general case of particles with different trap frequencies, where the usual approach of separating center-of-mass and relative motion fails. We develop an exact diagonalization approach to the coupling between center-of-mass and relative motion and numerically determine the spectrum of the system. At the same time, our approach allows us to treat the anharmonicity of the lattice potential exactly. Within the pseudopotential model, the center of the Feshbach resonance can be precisely determined from the experimental data.Comment: 9 pages, 7 figures, revised discussion of transfer efficienc

Improved glycerol utilization by a triacylglycerol-producing Rhodococcus opacus strain for renewable fuels

Background: Glycerol generated during renewable fuel production processes is potentially an attractive substrate for the production of value-added materials by fermentation. An engineered strain MITXM-61 of the oleaginous bacterium Rhodococcus opacus produces large amounts of intracellular triacylglycerols (TAGs) for lipid-based biofuels on high concentrations of glucose and xylose. However, on glycerol medium, MITXM-61 does not produce TAGs and grows poorly. The aim of the present work was to construct a TAG-producing R. opacus strain capable of high-cell-density cultivation at high glycerol concentrations. Results: An adaptive evolution strategy was applied to improve the conversion of glycerol to TAGs in R. opacus MITXM-61. An evolved strain, MITGM-173, grown on a defined medium with 16 g L[superscript −1] glycerol, produced 2.3 g L[superscript −1] of TAGs, corresponding to 40.4% of the cell dry weight (CDW) and 0.144 g g[superscript −1] of TAG yield per glycerol consumed. MITGM-173 was able to grow on high concentrations (greater than 150 g L[superscript −1]) of glycerol. Cultivated in a medium containing an initial concentration of 20 g L[superscript −1] glycerol, 40 g L[superscript −1] glucose, and 40 g L[superscript −1] xylose, MITGM-173 was capable of simultaneously consuming the mixed substrates and yielding 13.6 g L[superscript −1] of TAGs, representing 51.2% of the CDM. In addition, when 20 g L[superscript −1] glycerol was pulse-loaded into the culture with 40 g L[superscript −1] glucose and 40 g L[superscript −1] xylose at the stationary growth phase, MITGM-173 produced 14.3 g L[superscript −1] of TAGs corresponding to 51.1% of the CDW although residual glycerol in the culture was observed. The addition of 20 g L[superscript −1] glycerol in the glucose/xylose mix resulted in a TAG yield per glycerol consumed of 0.170 g g[superscript −1] on the initial addition and 0.279 g g[superscript −1] on the pulse addition of glycerol. Conclusion: We have generated a TAG-producing R. opacus MITGM-173 strain that shows significantly improved glycerol utilization in comparison to the parental strain. The present study demonstrates that the evolved R. opacus strain shows significant promise for developing a cost-effective bioprocess to generate advanced renewable fuels from mixed sugar feedstocks supplemented with glycerol.Sweetwater Energy, Inc.MIT Energy Initiativ

Metabolite profiling at the cellular and subcellular level reveals metabolites associated with salinity tolerance in sugar beet

Hossain MS, Persicke M, ElSayed AI, Kalinowski J, Dietz K-J. Metabolite profiling at the cellular and subcellular level reveals metabolites associated with salinity tolerance in sugar beet. Journal of Experimental Botany. 2017;68(21-22):5961-5976.Sugar beet is among the most salt-tolerant crops. This study aimed to investigate the metabolic adaptation of sugar beet to salt stress at the cellular and subcellular levels. Seedlings were grown hydroponically and subjected to stepwise increases in salt stress up to 300 mM NaCl. Highly enriched fractions of chloroplasts were obtained by nonaqueous fractionation using organic solvents. Total leaf metabolites and metabolites in chloroplasts were profiled at 3 h and 14 d after reaching the maximum salinity stress of 300 mM NaCl. Metabolite profiling by gas chromatography- mass spectrometry (GC-MS) resulted in the identification of a total of 83 metabolites in leaves and chloroplasts under control and stress conditions. There was a lower abundance of Calvin cycle metabolites under salinity whereas there was a higher abundance of oxidative pentose phosphate cycle metabolites such as 6-phosphogluconate. Accumulation of ribose-5-phosphate and ribulose-5-phosphate coincided with limitation of carbon fixation by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Increases in glycolate and serine levels indicated that photorespiratory metabolism was stimulated in salt-stressed sugar beet. Compatible solutes such as proline, mannitol, and putrescine accumulated mostly outside the chloroplasts. Within the chloroplast, putrescine had the highest relative level and probably assisted in the acclimation of sugar beet to high salinity stress. The results provide new information on the contribution of chloroplasts and the extra-chloroplast space to salinity tolerance via metabolic adjustment in sugar beet

Studies on the production of branched-chain alcohols in engineered Ralstonia eutropha

Wild-type Ralstonia eutropha H16 produces polyhydroxybutyrate (PHB) as an intracellular carbon storage material during nutrient stress in the presence of excess carbon. In this study, the excess carbon was redirected in engineered strains from PHB storage to the production of isobutanol and 3-methyl-1-butanol (branched-chain higher alcohols). These branched-chain higher alcohols can directly substitute for fossil-based fuels and be employed within the current infrastructure. Various mutant strains of R. eutropha with isobutyraldehyde dehydrogenase activity, in combination with the overexpression of plasmid-borne, native branched-chain amino acid biosynthesis pathway genes and the overexpression of heterologous ketoisovalerate decarboxylase gene, were employed for the biosynthesis of isobutanol and 3-methyl-1-butanol. Production of these branched-chain alcohols was initiated during nitrogen or phosphorus limitation in the engineered R. eutropha. One mutant strain not only produced over 180 mg/L branched-chain alcohols in flask culture, but also was significantly more tolerant of isobutanol toxicity than wild-type R. eutropha. After the elimination of genes encoding three potential carbon sinks (ilvE, bkdAB, and aceE), the production titer improved to 270 mg/L isobutanol and 40 mg/L 3-methyl-1-butanol. Semicontinuous flask cultivation was utilized to minimize the toxicity caused by isobutanol while supplying cells with sufficient nutrients. Under this semicontinuous flask cultivation, the R. eutropha mutant grew and produced more than 14 g/L branched-chain alcohols over the duration of 50 days. These results demonstrate that R. eutropha carbon flux can be redirected from PHB to branched-chain alcohols and that engineered R. eutropha can be cultivated over prolonged periods of time for product biosynthesis.United States. Dept. of EnergyUnited States. Advanced Research Projects Agency-Energ

Funktion und Regulation des Propionatstoffwechsels in Corynebacterium glutamicum

Plassmeier J. Funktion und Regulation des Propionatstoffwechsels in Corynebacterium glutamicum. Bielefeld (Germany): Bielefeld University; 2010

Task Collections

Within the research project LibRank we evaluated a sample of factors for relevance ranking in library information systems by using a test system with EconBiz data. EconBiz is an academic search portal for economics by the German National Library of Economics (ZBW - Zentralbibliothek für Wirtschaftswissenschaften, Leibnitz-Informationszentrum Wirtschaft). We applied standard procedures in Information Retrieval evaluation by using human relevance assessments. The research data were obtained in three evaluation runs and are published in 3 files including: A) Search queries with descriptions; B) Document URLs with relevance assessments; C) Ranking factors and weightings.Within the research project LibRank we evaluated a sample of factors for relevance ranking in library information systems by using a test system with EconBiz data. EconBiz is an academic search portal for economics by the German National Library of Economics (ZBW - Zentralbibliothek für Wirtschaftswissenschaften, Leibnitz-Informationszentrum Wirtschaft). We applied standard procedures in Information Retrieval evaluation by using human relevance assessments. The research data were obtained in three evaluation runs and are published in 3 files including: A) Search queries with descriptions; B) Document URLs with relevance assessments; C) Ranking factors and weightings

Harnessing the Biosphere: Natural Products and Biotechnology

What do the organisms of the biosphere, specifically microorganisms, have to offer to biotechnological endeavors? In this course we will focus on the production of biomolecules using microbial systems. We will discuss potential growth substrates (such as agricultural waste and carbon dioxide) that can be used and learn about both established and cutting-edge manipulation techniques in the field of synthetic biology. We will also cover the production of biofuels, bioplastics, amino acids (e.g. lysine), food additives (e.g. monosodium glutamate, MSG), specialty chemicals (e.g. succinate), and biopharmaceuticals (e.g. plasmids for gene therapy). This course is one of many Advanced Undergraduate Seminars offered by the Biology Department at MIT. These seminars are tailored for students with an interest in using primary research literature to discuss and learn about current biological research in a highly interactive setting. Many instructors of the Advanced Undergraduate Seminars are postdoctoral scientists with a strong interest in teaching

LibRank - New approaches to relevance ranking in Library Information Systems

Within the research project LibRank we evaluated a sample of factors for relevance ranking in library information systems by using a test system with EconBiz data. EconBiz is an academic search portal for economics by the German National Library of Economics (ZBW - Zentralbibliothek für Wirtschaftswissenschaften, Leibnitz-Informationszentrum Wirtschaft). We applied standard procedures in Information Retrieval evaluation by using human relevance assessments. The research data were obtained in three evaluation runs and are published in 3 files including: A) Search queries with descriptions; B) Document URLs with relevance assessments; C) Ranking factors and weightings.Unknow