Isolation and characterization of a new mucoid-free Klebsiella pneumoniae strain for 2,3-butanediol production

The secretion of mucoid substances by Klebsiella pneumoniae, a natural 2,3-butanediol (2,3-BD) hyper-producer, hinders its application in large-scale fermentation because of pathogenicity, fermentation instability, and downstream difficulty. In this study, 14 K. pneumoniae strains were isolated from a waste water treatment plant and their 2,3-BD production efficiencies were assessed with the strain K. pneumoniae DSM2026. Among various strains isolated, K. pneumoniae GSC010 and GSC112 produced relatively large amounts of 2,3-BD compared to other isolates; and their 2,3-BD production was consistent with DSM2026. Meanwhile, mucoidic characteristics of GSC010 were more or less similar to DSM2026, which was observed by scanning electron microscope (SEM) as a characteristic intercalated thread anchored on the surface of the cells. However, no polysaccharide materials were found in a non-mucoid cell, GSC112. Fed-batch culture of GSC112 with continuous glucose feeding resulted in the production of 2,3-BD at 52.4 g/l with 2,3-BD yield and overall productivity of 0.27 g/g glucose and 0.52 g/l/h, respectively. These results strongly suggest that the newly isolated mucoid-free K. pneumoniae GSC112 has potential for industrial production of 2,3-BD.Keywords: 2,3-Butanediol, Klebsiella pneumoniae, isolation, capsular polysaccharides, scanning electron microscop

The stability of graphene band structures against an external periodic perturbation; Na on Graphene

We report that the $\pi$ band of graphene sensitively changes as a function of an external potential induced by Na especially when the potential becomes periodic at low temperature. We have measured the band structures from the graphene layers formed on the 6H-SiC(0001) substrate using angle-resolved photoemission spectroscopy with synchrotron photons. With increasing Na dose, the $\pi$ band appears to be quickly diffused into background at 85 K whereas it becomes significantly enhanced its spectral intensity at room temperature (RT). A new parabolic band centered at $k\sim$1.15 \AA$^{-1}$ also forms near Fermi energy with Na at 85 K while no such a band observed at RT. Such changes in the band structure are found to be reversible with temperature. Analysis based on our first principles calculations suggests that the changes of the $\pi$ band of graphene be mainly driven by the Na-induced potential especially at low temperature where the potential becomes periodic due to the crystallized Na overlayer. The new parabolic band turns to be the $\pi$ band of the underlying buffer layer partially filled by the charge transfer from Na adatoms. The five orders of magnitude increased hopping rate of Na adatoms at RT preventing such a charge transfer explains the absence of the new band at RT.Comment: 6 pages and 6 figure

Mechanical Properties and Bioactivity of Poly(Lactic Acid) Composites Containing Poly(Glycolic Acid) Fiber and Hydroxyapatite Particles

To enhance the mechanical strength and bioactivity of poly(lactic acid) (PLA) to the level that can be used as a material for spinal implants, poly(glycolic acid) (PGA) fibers and hydroxyapatite (HA) were introduced as fillers to PLA composites. To improve the poor interface between HA and PLA, HA was grafted by PLA to form HA-g-PLA through coupling reactions, and mixed with PLA. The size of the HA particles in the PLA matrix was observed to be reduced from several micrometers to sub-micrometer by grafting PLA onto HA. The tensile and flexural strength of PLA/HA-g-PLA composites were increased compared with those of PLA/HA, apparently due to the better dispersion of HA and stronger interfacial adhesion between the HA and PLA matrix. We also examined the effects of the length and frequency of grafted PLA chains on the tensile strength of the composites. By the addition of unidirectionally aligned PGA fibers, the flexural strength of the composites was greatly improved to a level comparable with human compact bone. In the bioactivity tests, the growth of apatite on the surface was fastest and most uniform in the PLA/PGA fiber/HA-g-PLA composite

Preparation of ultra high loading supported Pt catalyst for direct methanol fuel cell

Carbon-supported Pt catalysts with ultra high Pt loading up to 90 wt% for the DMFC cathode were prepared by novel polyol process, and characterized by XRD, TEM, and single cell performance of DMFC. Highly dispersed Pt particles on carbon support with 40-75 wt% metal loading could be obtained with ca. 3 nm Pt particles in a single reduction step by optimizing the synthesis parameters. Furthermore, ultra high Pt loading up to 85 wt% catalysts were prepared by multiple reduction of Pt precursors. Thus prepared catalysts exhibited stacked microstructure and the sizes of Pt particles were less than 5 nm. The single cell performances of the catalysts prepared by multiple reductions were superior to that of the catalysts prepared by single reduction, which are attributed to the stacking structure of Pt particles and thinner electrode by using high metal loading.close2

Effects of mutation of 2,3-butanediol formation pathway on glycerol metabolism and 1,3-propanediol production by Klebsiella pneumoniae J2B

The current study investigates the impact of mutation of 2,3-butanediol (BDO) formation pathway on glycerol metabolism and 1,3-propanediol (PDO) production by lactate dehydrogenase deficient mutant of Klebsiella pneumoniae J2B. To this end, BDO pathway genes, budA, budB, budC and budO (whole-bud operon), were deleted from K. pneumoniae J2B Delta ldhA and the mutants were studied for glycerol metabolism and alcohols (PDO, BDO) production. Delta budO-mutant-only could completely abolish BDO production, but with reductions in cell growth and PDO production. By modifying the culture medium, the Delta budO mutant could recover its performance on the flask scale. However, in bioreactor experiments, the Delta budO mutant accumulated a significant amount of pyruvate (>73 mM) in the late phase and PDO production stopped concomitantly. Glycolytic intermediates of glycerol, especially glyceraldehyde-3-phosphate (G3P) was highly inhibitory to glycerol dehydratase (GDHt); its accumulation, followed by pyruvate accumulation, was assumed to be responsible for the Delta budO mutant's low PDO production.ope

Ordered mesoporous carbon as new support for direct methanol fuel cell: controlling of microporosity and graphitic character

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Isolation and characterization of the new Klebsiella pneumoniae J2B strain showing improved growth characteristics with reduced lipopolysaccharide formation

Klebsiella pneumoniae is a suitable biocatalyst for the production of 1,3-propanediol (1,3-PDO) and 3-hydroxypropionic acid (3-HP) from glycerol. However, its commercial applications have been impeded due to its poor growth characteristics and the excessive production of lipopolysaccharide (LPS). To overcome these limitations, a new K. pneumoniae J2B (KpJ2B) strain was isolated from municipal waste anaerobic digester samples. The shake flask cultivation of this new strain under aerobic conditions showed a specific growth rate of 0.92/h, which is 1.13 times higher than that achieved using the well studied K. pneumoniae DSMZ2026 (KpDSMZ). When the new strain was grown in a bioreactor under aerobic conditions using a fed-batch mode for 36 h, the biomass concentration (4.03 g/L CDW) and productivity (0.15 g/L/h) were almost 2.2 times higher than the corresponding values with KpDSMZ. Growth was accompanied by the production of 1,3-PDO (186 mM), lactic acid (235 mM), ethanol (170 mM), and acetic acid (92.2 mM) at significant levels, indicating the resistance of the strain to the inhibitory effects of these metabolites. A comparison of the SEM images and 2-keto-3-deoxyoctonate content (KpJ2B, 1.4 mu g/g CDW; KpDSMZ, 1.9 mu g/g CDW) confirmed the lower LPS content in the KpJ2B strain. Furthermore, this new isolate exhibited higher sensitivity towards a range of antibiotics and better sedimentation properties than the KpDSMZ strain. This suggests that KpJ2B is an attractive strain for industrial applications

Rational synthesis pathway for ordered mesoporous carbon with controllable 30- To 100-angstrom pores

A study has reported a facial synthesis strategy for the production of ordered mesoporous carbon (OMC) materials with systematically tuneable mesopore sizes in the range of 3-10 nm, where boric acid is utilized as a pore expanding agent. A spontaneous phase separation of the boron species, which is present in the precursor silica composite and contains sucrose and boric acid within the mesopores of a silica template, takes place within the carbonization process. This is expected to result in the subsequent formation of boron oxide and borosilicate nanolayers between the silica and carbon frameworks, which may result in an increased pore size for the OMC materials obtained. The synthesis of OMC materials with controllable pore sizes uses a mixed aqueous solution of boric acid and sucrose. The study has also suggested that OMC materials with tuneable pore sizes are expected to be highly beneficial for various practical applications, such as catalysis, adsorption, and separation.close464