Biosynthesis of non-sulfated high-molecular-weight glycosaminoglycans and specific-sized oligosaccharides.

Non-sulfated forms of glycosaminoglycans (NSGAGs) including hyaluronan, chondroitin and heparosan with high-molecular-weight (HMW) are extensively used biomaterials, while NSGAGs oligosaccharides display strong bioactivities. However, microbial production of HMW-NSGAGs and oligosaccharides with specific size are always challenging. Here, a membrane shield strategy was developed to produce HMW-NSGAGs by recruiting type II NSGAG synthases in Corynebacterium glutamicum. By enhancing precursor supplies and reinforcing cell membrane, the MWs of hyaluronan, heparosan and chondroitin reached 4100 kDa, 3000 kDa and 2400 kDa, respectively. In parallel, a synchronized depolymerization-polymerization strategy was developed by co-expressing NSGAGs synthases and lyases. With cell membrane as a filter, we achieved the direct biosynthesis of NSGAGs tetrasaccharides and disaccharides. The titers of chondroitin, hyaluronan and heparosan tetrasaccharides and disaccharides reached 10.9 g L-1, 12.1 g L-1 and 5.8 g L-1, respectively. The strategies developed here should also be applicable to the biosynthesis of other polysaccharides.

Hierarchical goethite nanoparticle and tin dioxide quantum dot anchored on reduced graphene oxide for long life and high rate lithium-ion storage.

The synergetic effect between two or more electrochemically active materials usually leads to superior lithium-ion storage performance. This work demonstrates a straightforward and effective approach to synthesize a reduced graphene oxide (RGO) encapsulated larger goethite (FeOOH) nanoparticles and smaller tin dioxide (SnO2) quantum dots hierarchical composite (SnO2@FeOOH/RGO). The synthesized SnO2@FeOOH/RGO composite exhibits encouraging lithium-ion storage capability than controlled SnO2/RGO and FeOOH/RGO samples with a stable specific capacity of 638 mAh·g-1 under a high current rate of 1000 mA·g-1 for 2000 continual cycles and good rate performance. The redox reaction between reductive metal-atoms or metal-ions and graphene oxide (GO) sheets guarantees an effective immobilization of corresponding nano-sized metal oxide and hydroxide crystals by the RGO framework. Furthermore, the engineered larger FeOOH crystals engage in lithium-ion storage and perform an ideal spacer between the restacked RGO sheets. Therefore, smaller SnO2 quantum dots' inherent excellent rate capability is extensively promoted due to the improvement of electrolyte diffusion and electron transfer condition. The sample design and fabrication method in this work might be developed for broader applications.

Influences of bioapatite mineral and fibril structure on the mechanical properties of chicken bone during the laying period.

Laying hens suffer from osteoporosis during their laying period, which causes bone fragility and susceptibility to fracture. This study evaluated the changes of mechanical properties of their bones during the laying period (from 18 to 77 wk) by using nano-indentation, atomic force microscope, X-Ray diffraction, and Raman spectroscopy. Results indicated that the crystallite sizes of bioapatite in femur decreased significantly from 34.45 to 29.26 nm during aging from 18 to 49 wk. Then, the value increased to 37.79 nm at 77 wk. Despite the abundance in bone (usually >50 wt.%), bioapatite mineral content showed no continuous enhancement during aging. The fibrils demonstrated more regular and organized structure during the laying period. Meanwhile the elastic moduli (E) and hardness (H) of femur increased from 10.84 to 18.39 GPa and 43.79 to 97.21 Vickers respectively during this period. The changes in mechanical properties are hence tightly related to the structure of bone (composed of both collagen and mineral), rather than directly related to the mineralogical properties of bone bioapatite. This study addressed the importance of the interaction between collagen and bioapatite mineral during the laying period of hens by microscopic, physicochemical, and mechanical analysis.

Longitudinal Study of the Effects of Environmental pH on the Mechanical Properties of Aspergillus niger.

The regulation of environmental pH is key to the health of an ecosystem, influencing the metabolic activity, growth, and development of organisms within it. Although pH values can be measured by a wide range of readily available technologies ranging from fluorescent dyes and nanosensors, these cannot reveal the history of environmental pH from before monitoring begins. This information is sometimes crucial for piecing together what has happened to an ecosystem, and our long-term goal is therefore to develop technologies capable of obtaining it. Here, we propose monitoring environmental pH over time by tracking mechanical properties of a common fungus. As a first step toward obtaining a time history of pH, we evaluate the effect of pH upon the effective indentation modulus of spores and hyphae of Aspergillus niger. We report that the indentation modulus of this phosphorus-solubilizing fungus, obtained through atomic force microscopy and nanoindentation, correlated with environmental acidity. We observed a significant, monotonic increase in moduli over the course of incubation in an acidic environment, but no change in moduli over time for incubation in a neutral environment. Results show promise for using our scheme to detect and track environmental pH over time, and more broadly for using a microorganism's mechanical properties as a biomarker for environmental detection.

Tunable and switchable dual-wavelength mode-locked Tm3+-doped fiber laser based on a fiber taper.

We demonstrate a self-starting dual-wavelength mode-locked fiber laser at a 2 µm spectral region by using a fiber taper in a Tm3+-doped ring fiber cavity. The fiber taper fabricated with a flame brushing technique was used as a periodic filter with a modulation depth of ~3.61 dB and a modulation period of ~7.3 nm, respectively. Diverse dual-wavelength regimes including continuous wave (CW)/multi-soliton, soliton/multi-soliton, and soliton/soliton regimes were obtained by adjusting pump power. Wavelength tuning for the dual-wavelength was also precisely controllable through stretching the fiber taper carefully. The tuning range was ~7 nm which was limited by the modulation period of the taper. By inserting a 10.0 m dispersion compensation fiber (DCF) into the fiber cavity, a stable dual-wavelength dissipative-soliton operation was obtained at 2 µm spectral region for the first time.

A study of organic acid production in contrasts between two phosphate solubilizing fungi: Penicillium oxalicum and Aspergillus niger.

Phosphate solubilizing fungi (PSF) have huge potentials in enhancing release of phosphorus from fertilizer. Two PSF (NJDL-03 and NJDL-12) were isolated and identified as Penicillium oxalicum and Aspergillus niger respectively in this study. The quantification and identification of organic acids were performed by HPLC. Total concentrations of organic acids secreted by NJDL-03 and NJDL-12 are ~4000 and ~10,000 mg/L with pH values of 3.6 and 2.4 respectively after five-days culture. Oxalic acid dominates acidity in the medium due to its high concentration and high acidity constant. The two fungi were also cultured for five days with the initial pH values of the medium varied from 6.5 to 1.5. The biomass reached the maximum when the initial pH values are 4.5 for NJDL-03 and 2.5 for NJDL-12. The organic acids for NJDL-12 reach the maximum at the initial pH = 5.5. However, the acids by NJDL-03 continue to decrease and proliferation of the fungus terminates at pH = 2.5. The citric acid production increases significantly for NJDL-12 at acidic environment, whereas formic and oxalic acids decrease sharply for both two fungi. This study shows that NJDL-12 has higher ability in acid production and has stronger adaptability to acidic environment than NJDL-03.