Compression and morphological properties of a bio-based polyurethane foam with aluminum hydroxide

Compression and morphological evaluation of a new bio-based polyurethane foam (PUF) with aluminum hydroxide (ATH) added as flame retardant were carried out. The PUF was obtained from a blend of vegetable oils. Compression behavior of the polyurethane with different mass fractions of flame retardant (ATH) was investigated according to ASTM D1621–16. The ATH addition highly increased the compression yield strength of the specimens, going from 0.85 MPa (no ATH) to 2.34 MPa ( + 50%wt ATH). The compression yield strain did not show a noteworthy difference up to 40% ATH, presenting a significant decrement in the PUF + 50%ATH. The compression elasticity modulus increased from 15.40 MPa (no ATH) up to 139.77 MPa ( + 50%wt ATH). SEM images were used in order to evaluate the morphological structure of the foam. Regarding the cell sizes, there was no pattern observed, therefore, the cell sizes were adopted as random. The shapes of the cells were detected as elliptical in two different directions in the same cross-sectional area. The digital image correlation (DIC) technique showed higher strain values where the transverse ellipsoid-shaped cells were located, therefore, the load-oriented ellipsoids presented higher stiffness. Thus, the results for PUF with addition of ATH show that the bio-based material presented an important improvement in the compression properties, which allows this material to become more useful for different applications, such as furniture, building and automobile industries, as well as sandwich structures.

Positive regulation of MarR-type regulator slnO and improving salinomycin production of Streptomyces albus by multiple transcriptional regulations

The purpose of this study is to explore the function of MarR-family regulator slnO. In addition, the high-yield strain of salinomycin was constructed by using combined regulation strategies. Firstly the slnO gene over-expression strain (GO) was constructed in Streptomyces albus. Compared to wild type (WT) strain，salinomycin production in GO strain was increased about 28%. Electrophoretic mobility gel shift assays (EMSAs) confirmed that SlnO protein can bind specifically to the intergenic region of slnN-slnO, slnQ-slnA1 and slnF-slnT. qRT-PCR experiments also showed that slnA1, slnF, and slnT1 were significantly up-regulated, while the expression level of the slnN gene was down-regulated in GO strain. Secondly, slnN gene deletion strain (slnNDM) was used as the starting strain, and the pathway specific gene slnR in salinomycin gene cluster was over expressed in slnNDM. The new strain was named ZJUS01. The yield of salinomycin in ZJUS01 strain was 25% and 56% higher than that in slnNDM strain and WT strain. Above results indicate that the slnO gene has a positive regulation effect on the biosynthesis of salinomycin. Meanwhile, the yield of salinomycin could be greatly increased by manipulating multiple transcriptional regulations.

Deformation mechanism of copper reinforced by three-dimensional graphene under torsion and tension

The mechanical behaviors of uniaxial torsional and tensional copper nanorod embedded with sp2-type hybrid graphene nanosheets (3DG/Cu) were investigated systematically using molecular dynamics methods. During the torsion process, graphene expanded the plastic deformation region of copper, while the plastic deformation in monocrystalline Cu cases was limited to a smaller area. 3DG/Cu responded to the torsion by one more plastic stage when plastic deformation spread along the length after the elastic response. Graphene improved the torsional loading capacity of the composite material, greatly extending the effective response range of the material by distributing the deformation of copper along with the graphene rather than being concentrated at a certain position like monocrystalline Cu. Generally, as the length of the model increased, this enhancement decreased. The copper portion of 3DG/Cu was divided into three areas during uniaxial tensile, a static region, a quasi-static region of the middle portion where the shear and necking occurred, and a dynamic area near the loading end. However, the inside graphene kept continuous until fracture. Furthermore, graphene improved the yield strain of copper by maintaining intact after copper failure. The greater the pre-loaded torsion angle, the smaller the yield strength and Young's modulus of 3DG/Cu.

Pectin self-assembly and its disruption by water: Insights into plant cell wall mechanics

Plant cell walls undergo multiple cycles of dehydration and rehydration during their life. Calcium crosslinked low methoxy pectin is a major constituent of plant cell walls. Understanding the dehydration-rehydration behavior of pectin gels may shed light on the water transport and mechanics of plant cells. In this work, we report the contributions of microstructure to the mechanics of pectin-Ca gels subjected to different extents of dehydration and subsequent rehydration. This is investigated using a pectin gel composition that forms ‘egg-box bundles’, a characteristic feature of the microstructure of low methoxy pectin-Ca gels. Large Amplitude Oscillatory Shear (LAOS) rheology along with Small Angle Neutron Scattering and Near Infrared (NIR) spectroscopy on pectin gels are used to elucidate the mechanical and microstructural changes during dehydration-rehydration cycles. As the extent of dehydration increase, the reswelling ability, strain-stiffening behavior and the yield strain decreases. These effects are more prominent at faster rates of dehydration and are not completely reversible upon rehydration to the initial undried state. Microstructural changes due to the aggregation of egg-box bundles and single chains and the associated changes in the water configurations lead to these irreversible changes.

Uncovering and Engineering a Mini-Regulatory Network of the TetR-Family Regulator SACE_0303 for Yield Improvement of Erythromycin in Saccharopolyspora erythraea

Erythromycins produced by Saccharopolyspora erythraea have broad-spectrum antibacterial activities. Recently, several TetR-family transcriptional regulators (TFRs) were identified to control erythromycin production by multiplex control modes; however, their regulatory network remains poorly understood. In this study, we report a novel TFR, SACE_0303, positively correlated with erythromycin production in Sac. erythraea. It directly represses its adjacent gene SACE_0304 encoding a MarR-family regulator and indirectly stimulates the erythromycin biosynthetic gene eryAI and resistance gene ermE. SACE_0304 negatively regulates erythromycin biosynthesis by directly inhibiting SACE_0303 as well as eryAI and indirectly repressing ermE. Then, the SACE_0303 binding site within the SACE_0303-SACE_0304 intergenic region was defined. Through genome scanning combined with in vivo and in vitro experiments, three additional SACE_0303 target genes (SACE_2467 encoding cation-transporting ATPase, SACE_3156 encoding a large transcriptional regulator, SACE_5222 encoding α-ketoglutarate permease) were identified and proved to negatively affect erythromycin production. Finally, by coupling CRISPRi-based repression of those three targets with SACE_0304 deletion and SACE_0303 overexpression, we performed stepwise engineering of the SACE_0303-mediated mini-regulatory network in a high-yield strain, resulting in enhanced erythromycin production by 67%. In conclusion, the present study uncovered the regulatory network of a novel TFR for control of erythromycin production and provides a multiplex tactic to facilitate the engineering of industrial actinomycetes for yield improvement of antibiotics.

Effect of Hard Plastic Waste on the Quality of Recycled Polypropylene Blends

The recycling of plastic waste is undergoing fast growth due to environmental, health and economic issues, and several blends of post-consumer and post-industrial polymeric materials have been characterized in recent years. However, most of these researches have focused on plastic containers and packaging, neglecting hard plastic waste. This study provides the first experimental characterization of different blends of hard plastic waste and virgin polypropylene in terms of melt index, differential scan calorimetry (DSC), thermogravimetric analysis (TGA), mechanical properties (tensile, impact and Shore hardness) and Vicat softening test. Compared to blends based on packaging plastic waste, significant differences were observed in terms of melt flow index (about 10 points higher for hard plastic waste). Mechanical properties, in particular yield strain, were instead quite similar (between 5 and 9%), despite a higher standard deviation being observed, up to 10%, probably due to incomplete homogenization. Results demonstrate that these worse performances could be mainly attributed to the presence of different additives, as well as to the presence of impurities or traces of other polymers, other than incomplete homogenization. On the other hand, acceptable results were obtained for selected blends; the optimal blending ratio was identified as 78% post-consumer waste and 22% post-industrial waste, meeting the requirement for injection molding and thermoforming.

A Method for Rapid Prediction of Edge Defects in Cold Roll Forming Process

In order to implement rapid prediction of edge defects in the cold roll forming process, a new analytical method based on the mean longitudinal strain of the racks is presented. A cubic spline curve with the parameters of the cumulative chord length is applied to fit the corresponding points and center points of different passes, and fitting curves are obtained. As the cold roll forming is micro-tension forming, the tensions between racks are ignored. Then the mean longitudinal strains between racks are obtained. By comparing the mean longitudinal strain between racks and the yield strain of the material, we can judge whether there are defects at the edges. Finally, the reasonableness of this method is illustrated and validated by an example. With this method, the roll forming effect can be quickly predicted, and the position where a greater longitudinal strain occurred can be determined. In order to prevent the defects, the deformation angles need to be modified when the result is beyond the yield strain. To further prove the correctness of the theory, the results of the analytical method are compared with the ones of the non-linear finite element software ABAQUS. The analytical results have the same trend as the finite element results. This method can provide useful guidance to the actual design process.

Metabolomic Analysis of Biosynthesis Mechanism of ε-Polylysine Produced by Streptomyces diastatochromogenes

ε-Polylysine (ε-PL), a natural preservative with broad-spectrum antimicrobial activity, has been widely used as a green food additive, and it is now mainly produced by Streptomyces in industry. In the previous study, strain 6#-7 of high-yield ε-PL was obtained from the original strain TUST by mutagenesis. However, the biosynthesis mechanism of ε-PL in 6#-7 is still unclear. In this study, the metabolomic analyses of the biosynthesis mechanism of ε-PL in both strains are investigated. Results show that the difference in metabolisms between TUST and 6#-7 is significant. Based on the results of both metabolomic and enzymatic activities, a metabolic regulation mechanism of the high-yield strain is revealed. The transport and absorption capacity for glucose of 6#-7 is improved. The enzymatic activity benefits ε-PL synthesis, such as pyruvate kinase and aspartokinase, is strengthened. On the contrary, the activity of homoserine dehydrogenase in the branched-chain pathways is decreased. Meanwhile, the increase of trehalose, glutamic acid, etc. makes 6#-7 more resistant to ε-PL. Thus, the ability of the mutagenized strain 6#-7 to synthesize ε-PL is enhanced, and it can produce more ε-PLs compared with the original strain. For the first time, the metabolomic analysis of the biosynthesis mechanism of ε-PL in the high-yield strain 6#-7 is investigated, and a possible mechanism is then revealed. These findings provide a theoretical basis for further improving the production of ε-PL.

Utilization efficiency of human milk oligosaccharides by human-associated Akkermansia is strain-dependent

Akkermansia muciniphila are mucin degrading bacteria found in the human gut and are often associated with positive human health. However, despite being detected as early as one month of age, little is known about the role of Akkermansia in the infant gut. Human milk oligosaccharides (HMOs) are abundant components of human milk and are structurally similar to the oligosaccharides that comprise mucin, the preferred growth substrate of human-associated Akkermansia. A limited subset of intestinal bacteria has been shown to grow well on HMOs and mucin. We therefore examined the ability of genomically diverse strains of Akkermansia to grow on HMOs. First, we screened 85 genomes representing the four known Akkermansia phylogroups to examine their metabolic potential to degrade HMOs. Furthermore, we examined the ability of representative isolates to grow on individual HMOs in a mucin background and analyzed the resulting metabolites. All Akkermansia genomes were equipped with an array of glycoside hydrolases associated with HMO-deconstruction. Representative strains were all able to grow on HMOs with varying efficiency and growth yield. Strain CSUN-19 belonging to the AmIV phylogroup, grew to the highest level in the presence of fucosylated and sialylated HMOs. This activity may be partially related to the increased copy numbers and/or the enzyme activities of the α-fucosidases, β-sialidases, and β-galactosidases. Utilization of HMOs by strains of Akkermansia suggests that ingestion of HMOs by an infant may enrich for these potentially beneficial bacteria. Further studies are required to realize this opportunity and deliver long-lasting metabolic benefits to the human host.

Comparative transcriptomic analysis of two Saccharopolyspora spinosa strains reveals the relationships between primary metabolism and spinosad production

Saccharopolyspora spinosa is a well-known actinomycete for producing the secondary metabolites, spinosad, which is a potent insecticides possessing both efficiency and safety. In the previous researches, great efforts, including physical mutagenesis, fermentation optimization, genetic manipulation and other methods, have been employed to increase the yield of spinosad to hundreds of folds from the low-yield strain. However, the metabolic network in S. spinosa still remained un-revealed. In this study, two S. spinosa strains with different spinosad production capability were fermented and sampled at three fermentation periods. Then the total RNA of these samples was isolated and sequenced to construct the transcriptome libraries. Through transcriptomic analysis, large numbers of differentially expressed genes were identified and classified according to their different functions. According to the results, spnI and spnP were suggested as the bottleneck during spinosad biosynthesis. Primary metabolic pathways such as carbon metabolic pathways exhibited close relationship with spinosad formation, as pyruvate and phosphoenolpyruvic acid were suggested to accumulate in spinosad high-yield strain during fermentation. The addition of soybean oil in the fermentation medium activated the lipid metabolism pathway, enhancing spinosad production. Glutamic acid and aspartic acid were suggested to be the most important amino acids and might participate in spinosad biosynthesis.