Co-utilization of glucose and xylose for the production of poly-ß-hydroxybutyrate (PHB) by Sphingomonas sanxanigenens NX02.

BACKGROUND: Poly-ß-hydroxybutyrate (PHB), produced by a variety of microbial organisms, is a good substitute for petrochemically derived plastics due to its excellent properties such as biocompatibility and biodegradability. The high cost of PHB production is a huge barrier for application and popularization of such bioplastics. Thus, the reduction of the cost is of great interest. Using low-cost substrates for PHB production is an efficient and feasible means to reduce manufacturing costs, and the construction of microbial cell factories is also a potential way to reduce the cost. RESULTS: In this study, an engineered Sphingomonas sanxanigenens strain to produce PHB by blocking the biosynthetic pathway of exopolysaccharide was constructed, and the resulting strain was named NXdE. NXdE could produce 9.24 ± 0.11 g/L PHB with a content of 84.0% cell dry weight (CDW) using glucose as a sole carbon source, which was significantly increased by 76.3% compared with the original strain NX02. Subsequently, the PHB yield of NXdE under the co-substrate with different proportions of glucose and xylose was also investigated, and results showed that the addition of xylose would reduce the PHB production. Hence, the Dahms pathway, which directly converted D-xylose into pyruvate in four sequential enzymatic steps, was enhanced by overexpressing the genes xylB, xylC, and kdpgA encoding xylose dehydrogenase, gluconolactonase, and aldolase in different combinations. The final strain NX02 (ΔssB, pBTxylBxylCkdpgA) (named NXdE II) could successfully co-utilize glucose and xylose from corn straw total hydrolysate (CSTH) to produce 21.49 ± 0.67 g/L PHB with a content of 91.2% CDW, representing a 4.10-fold increase compared to the original strain NX02. CONCLUSION: The engineered strain NXdE II could co-utilize glucose and xylose from corn straw hydrolysate, and had a significant increase not only in cell growth but also in PHB yield and content. This work provided a new host strain and strategy for utilization of lignocellulosic biomass such as corn straw to produce intracellular products like PHB.

A high strength, low friction, and biocompatible hydrogel from PVA, chitosan and sodium alginate for articular cartilage.

Developing articular cartilage substitutes required a combination of high compressive strength, excellent biocompatibility and low friction. Despite great success in tough hydrogels, this combination was hardly realized. Herein, a high strength, low friction, and biocompatible hydrogel was obtained by freezing-thawing polyvinyl alcohol and chitosan aqueous solutions three times, followed with soaking in sodium alginate aqueous solution. Owing to the synergy of crystalline domains, hydrogen bonds, and ionic interactions, the obtained hydrogel exhibited high strength (maximum compressive strength = 141 MPa). Because of the reversible linkages, the gel was also creep-resistant (recovery efficiency = 93%). Benefitted from the negative carboxyl groups from sodium alginate, the water lubrication layer between the gel and the opposing surface was thickened greatly, resulting in a low coefficient of friction (0.044). The biocompatible materials and green progress led to excellent cell compatibility. All these merits made it an ideal substitute for articular cartilage.

A dual luminescent sensor coordination polymer for simultaneous determination of ascorbic acid and tryptophan.

Simultaneous high sensitivity detection of biomolecules is important for research in medicine, living cells and environmental samples. In this work, a water stable coordination polymer, [Cd2(bptc)(4,4'-bpy)(H2O)3]ˑH2O 1 (H4bptc = 2,3,3',4'-biphenyl tetracarboxylic acid, 4,4'-bpy = 4,4'-bipyridine), was designed and successfully synthesized as a luminescent sensor for simultaneous recognition of Ascorbic Acid (AA) and L-Tryptophan (L-Trp) based on luminescent -OFF and -ON, respectively. Importantly, the proposed sensing system showed an excellent performance with high KSV values of 4.85 × 104 M-1, 9.60 × 107 M-1 and low limit of detection (LOD) of 0.28 nM, 63 nM, respectively. In addition, the probable mechanisms are also discussed. The luminescent quenching behavior by AA can be mainly attributed to the static resonance energy transfer between complex 1 and the analytes. Whereas the enhancing effect of L-Trp comes from the intrinsic strong luminescence for L-Trp itself and photo-competitive mechanism between CP 1 sensor and L-Trp, supposedly. In addition, the repeatability of both systems were also investigated.

Biotemplated hierarchical nanostructure of layered double hydroxides with improved photocatalysis performance.

We report a biomorphic hierarchical mixed metal oxide (MMO) framework through a biotemplated synthesis method. A uniform Al(2)O(3) coating was deposited on the surface of the biotemplate with an atomic layer deposition (ALD) process, and the film of ZnAl-layered double hydroxide (ZnAl-LDH), which faithfully inherits the surface structure of the biotemplate, was prepared by an in situ growth technique. Subsequently, a polycrystal ZnAl-MMO framework obtained by calcination of the LDH precursor has been demonstrated as an effective and recyclable photocatalyst for the decomposition of dyes in water, owing to its rather high specific surface area and hierarchical distribution of pore size. Therefore, the new strategy reported in this work can be used to fabricate a variety of biomorphic LDHs as well as MMO frameworks through replication of complicated and hierarchical biological structures for the purpose of catalysis, adsorbents, and other potential applications.