[Expression of ß-xylosidase An-xyl from Aspergillus niger and characterization of its xylose tolerance].

The hydrolysis of xylo-oligosaccharides catalyzed by ß-xylosidase plays an important role in the degradation of lignocellulose. However, the enzyme is easily inhibited by its catalytic product xylose, which severely limits its application. Based on molecular docking, this paper studied the xylose affinity of Aspergillus niger ß-xylosidase An-xyl, which was significantly differentially expressed in the fermentation medium of tea stalks, through cloning, expression and characterization. The synergistic degradation effect of this enzyme and cellulase on lignocellulose in tea stems was investigated. Molecular docking showed that the affinity of An-xyl to xylose was lower than that of Aspergillus oryzae ß-xylosidase with poor xylose tolerance. The Ki value of xylose inhibition constant of recombinant-expressed An-xyl was 433.2 mmol/L, higher than that of most ß-xylosidases of the GH3 family. The Km and Vmax towards pNPX were 3.6 mmol/L and 10 000 µmol/(min·mL), respectively. The optimum temperature of An-xyl was 65 ℃, the optimum pH was 4.0, 61% of the An-xyl activity could be retained upon treatment at 65 ℃ for 300 min, and 80% of the An-xyl activity could be retained upon treatment at pH 2.0-8.0 for 24 h. The hydrolysis of tea stem by An-xyl and cellulase produced 19.3% and 38.6% higher reducing sugar content at 2 h and 4 h, respectively, than that of using cellulase alone. This study showed that the An-xyl mined from differential expression exhibited high xylose tolerance and higher catalytic activity and stability, and could hydrolyze tea stem lignocellulose synergistically, which enriched the resource of ß-xylosidase with high xylose tolerance, thus may facilitate the advanced experimental research and its application.

Exolytic products of alginate by the immobilized alginate lyase confer antioxidant and antiapoptotic bioactivities in human umbilical vein endothelial cells.

Alginate is a natural polysaccharide resource abundant in brown algae and it can be cleaved into alginate oligosaccharides by alginate lyase. Alginate lyases and the bioactive alginate oligosaccharides have been applied in diverse fields such as pharmaceutical therapy and nutraceutical supplementation. Immobilized enzymes greatly facilitate their industrial application owing to their reusability, stability, and tunability. In this study, magnetic Fe3O4 nanoparticles were synthesized and used to immobilize an exolytic alginate lyase AlgL17 that was characterized previously. The immobilized AlgL17 demonstrated enhanced thermal and pH tolerance, extended storage stability, and moderate reusability. The mass spectrum indicated the specific activity of the immobilized AlgL17 to release alginate oligosaccharides (AOS) from alginate polysaccharide. The produced AOS exhibited their antioxidant and antiapoptotic activities in H2O2-stressed human umbilical vein endothelial cells by upregulation of reactive oxygen species scavenging activities and attenuation of the caspase-mediated apoptosis pathway.

Two-dimensional liquid chromatography analysis of all-trans-, 9-cis-, and 13-cis-astaxanthin in raw extracts from Phaffia rhodozyma.

An effective two-dimensional liquid chromatography method has been established for the analysis of all-trans-astaxanthin and its geometric isomers from Phaffia rhodozyma employing a C18 column at the first dimension and a C30 column in the second dimension, connected by a 10-port valve using the photo-diode array detector. The regression equation of astaxanthin calibration curve was established, and the precision and accuracy values were found to be in the range of 0.32-1.14% and 98.21-106.13%, respectively. By using two-dimensional liquid chromatography, it was found that day light, ultrasonic treatment, and heat treatment have significant influence on the content of all-trans-astaxanthin in the extract from P. rhodozyma due to the transformation of all-trans-astaxanthin to cis-astaxanthin. The day light and ultrasonic treatments more likely transform all-trans-astaxanthin to 9-cis-astaxanthin, and the thermal treatment transforms all-trans-astaxanthin to 13-cis-astaxanthin. These results indicate that the two-dimensional liquid chromatography method can facilitate monitoring astaxanthin isomerization in the raw extract from P. rhodozyma. In addition, the study will provide a general reference for monitoring other medicals and bioactive chemicals with geometric isomers.

Suppressive Interaction Approach for Masking Stale Note of Instant Ripened Pu-Erh Tea Products.

The unpleasant stale note is a negative factor hindering the consumption of instant ripened Pu-erh tea products. This study focused on investigating volatile chemicals in instant ripened Pu-erh tea that could mask the stale note via sensory evaluation, gas chromatography-mass spectrometry (GC-MS), and gas chromatography-olfactometry (GC-O) analyses. GC-MS and GC-O analyses showed that linalool, linalool oxides, trans-ß-ionone, benzeneacetaldehyde, and methoxybenzenes were the major aroma contributors to the simultaneous distillation and extraction (SDE) extract of instant ripened Pu-erh tea. Sensory evaluation showed that the SDE extract had a strong stale note, which was due to methoxybenzenes. By investigating suppressive interaction among flavour components, the stale note from methoxybenzenes was shown to have reciprocal masking interactions with sweet, floral, and green notes. Moreover, the validation experiment showed that the addition of 40 µg/mL of trans-ß-ionone in the instant ripened Pu-erh tea completely masked the stale note and improved the overall aromatic acceptance. These results elucidate the volatile chemicals that could mask the stale note of instant ripened Pu-erh tea products, which might help to develop high quality products made from instant ripened Pu-erh tea.

Identification and Characterization of the Tyrosinase Inhibitory Activity of Caffeine from Camellia Pollen.

Tyrosinase inhibitors are important in cosmetic, medical, and food industries due to their regulation of melanin production. A tyrosinase inhibitor was purified from Camellia pollen using high-speed countercurrent chromatography and preparative high-performance liquid chromatography and was identified as caffeine by NMR and mass spectrometry. It showed strong mushroom tyrosinase inhibitory activity with an IC50 of 18.5 ± 2.31 µg/mL in a noncompetitive model. The caffeine did not interact with copper ions in the active center of the enzyme but could quench fluorescence intensity and change the secondary conformation of this tyrosinase. A molecular dynamics simulation showed that caffeine bound this tyrosinase via Lys379, Lys 376, Asp357, Glu356, Thr308, Gln307, Asp312, and Trp358, thus changing the binding sites of l-tyrosine and the loop conformation adjacent to the active center. In vitro cell model analysis revealed that caffeine exhibited significant inhibitory effects on both intracellular tyrosinase activity and melanin production of B16-F10 melanoma cells in a concentration-dependent manner. These comprehensive results suggest that caffeine is a strong tyrosinase inhibitor that has the potential to be developed as skin-whitening agents in the cosmetics and pharmaceutical industries or as antibrowning agents in the food industry.

Maghemite (γ-Fe2O3) nanoparticles enhance dissimilatory ferrihydrite reduction by Geobacter sulfurreducens: Impacts on iron mineralogical change and bacterial interactions.

Microbially mediated bioreduction of iron oxyhydroxide plays an important role in the biogeochemical cycle of iron. Geobacter sulfurreducens is a representative dissimilatory iron-reducing bacterium that assembles electrically conductive pili and cytochromes. The impact of supplementation with γ-Fe2O3 nanoparticles (NPs) (0.2 and 0.6 g) on the G. sulfurreducens-mediated reduction of ferrihydrite was investigated. In the overall performance of microbial ferrihydrite reduction mediated by γ-Fe2O3 NPs, stronger reduction was observed in the presence of direct contact with γ-Fe2O3 NPs than with indirect contact. Compared to the production of Fe(II) derived from biotic modification with ferrihydrite alone, increases greater than 1.6- and 1.4-fold in the production of Fe(II) were detected in the biotic modifications in which direct contact with 0.2 g and 0.6 g γ-Fe2O3 NPs, respectively, occurred. X-ray diffraction analysis indicated that magnetite was a unique representative iron mineral in ferrihydrite when active G. sulfurreducens cells were in direct contact with γ-Fe2O3 NPs. Because of the sorption of biogenic Fe(II) onto γ-Fe2O3 NPs instead of ferrihydrite, the addition of γ-Fe2O3 NPs could also contribute to increased duration of ferrihydrite reduction by preventing ferrihydrite surface passivation. Additionally, electron microscopy analysis confirmed that the direct addition of γ-Fe2O3 NPs stimulated the electrically conductive pili and cytochromes to stretch, facilitating long-range electron transfer between the cells and ferrihydrite. The obtained findings provide a more comprehensive understanding of the effects of iron oxide NPs on soil biogeochemistry.

Strong Near-Infrared Absorbing and Biocompatible CuS Nanoparticles for Rapid and Efficient Photothermal Ablation of Gram-Positive and -Negative Bacteria.

Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) are the most common infectious bacteria in our daily life, and seriously affect human's health. Because of the frequent and extensive use of antibiotics, the microbial strains forming drug resistance have become more and more difficult to deal with. Herein, we utilized bovine serum albumin (BSA) as the template to synthesize uniform copper sulfide (CuS) nanoparticles via a biomineralization method. The as-prepared BSA-CuS nanocomposites showed good biocompatibility and strong near-infrared absorbance performance and can be used as an efficient photothermal conversion agent for pathogenic bacteria ablation with a 980 nm laser at a low power density of 1.59 W/cm2. The cytotoxicity of BSA-CuS nanocomposite was investigated using skin fibroblast cells and displayed good biocompatibility. Furthermore, the antibacterial tests indicated that BSA-CuS nanocomposite showed no antibacterial activity without NIR irradiation. In contrast, they demonstrated satisfying killing bacterial ability in the presence of NIR irradiation. Interestingly, S. aureus and E. coli showed various antibacterial mechanisms, possibly because of the different architectures of bacterial walls. Considering the low cost, easy preparation, excellent biocompatibility and strong photothermal convention efficiency (24.68%), the BSA-CuS nanocomposites combined with NIR irradiation will shed bright light on the treatment of antibiotic-resistant pathogenic bacteria.

Dual roles of AQDS as electron shuttles for microbes and dissolved organic matter involved in arsenic and iron mobilization in the arsenic-rich sediment.

Microbially-mediated arsenic (As) metabolism and iron (Fe) bioreduction from sediments play crucial roles in global As/Fe cycle, and their mobilization is associated with the various effects within the alliance of "mediator-bacteria-DOM (Dissolved Organic Matter)". The gradient levels (0.05, 0.10 and 1.00mM) of sodium anthraquinone-2,6-disulphonate (AQDS) as a mediator were investigated for their impact on reductive dissolution of As(V) and Fe(III) from arsenic-rich sediment. For the overall performance of AQDS-mediated reductive dissolution on As(V) and Fe(III), a more positive effect resulting from 0.05mM AQDS was observed compared to 0.10mM, whereas an inhibitory effect was observed with 1.00mM. Compared to the biotic supplementation with acetate as electron donors, approximately 13- and 6-fold increased levels of As(III) were released with 0.05 and 0.10mM, respectively, compared to 1.00mM AQDS (107.51µg/L), and approximately 4- and 3-fold increased Fe(II) levels (40.72mg/L) were observed during the same conditions. Multiple-dynamic effects of "bacteria-AQDS-DOM", which result from AQDS, shifted the microbial community and synchronously derived terrestrial DOM, which potentially changes the DOM substrate and complex formation of As(III)-Fe(II)-humic DOM. High-throughput sequencing results indicated an increase in the abundance of metal-reducing bacteria (e.g., Bacillus (>16%), Lactococcus (>13%), Pseudomonas (>4%) and Geobacter (>3%)) when supplemented with 0.05 and 0.10mM of AQDS. However, a boost increasing the abundance of metal oxidizing bacteria was observed with Alicyclobacillus (>16%), Burkholderia (>7%), and Bradyrhizobium (>5%) upon supplementation with 1.00mM AQDS. These novel insights have profound environmental implications and significance in terms of engineering, not only for understanding the cycle of As/Fe in sediment biochemical processes but for considering future alternative bioremediation treatments.

Nitrogen and phosphorus removal coupled with carbohydrate production by five microalgae cultures cultivated in biogas slurry.

In this study, five microalgae strains were cultured for their ability to survive in biogas slurry, remove nitrogen resources and accumulate carbohydrates. It was proved that five microalgae strains adapted in biogas slurry well without ammonia inhibition. Among them, Chlorella vulgaris ESP-6 showed the best performance on carbohydrate accumulation, giving the highest carbohydrate content of 61.5% in biogas slurry and the highest ammonia removal efficiency and rate of 96.3% and 91.7mg/L/d respectively in biogas slurry with phosphorus and magnesium added. Additionally, the absence of phosphorus and magnesium that can be adverse for biomass accumulation resulted in earlier timing of carbohydrate accumulation and magnesium was firstly recognized and proved as the influence factor for carbohydrate accumulation. Microalgae that cultured in biogas slurry accumulated more carbohydrate in cell, making biogas slurry more suitable medium for the improvement of carbohydrate content, thus can be regarded as a new strategy to accumulate carbohydrate.

Production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from excess activated sludge as a promising substitute of pure culture.

This study aimed to investigate the feasibility and technology to harvest poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) by mixed culture. Copolymer PHBHHx, usually fermented by pure strains, was reported to be synthesized from activated sludge for the first time. Sodium laurate was used as the sole carbon substrate for sludge acclimation and PHBHHx accumulation. Batch experiments were designed to look into the impact of the carbon, nitrogen, phosphorus and oxygen supply on PHBHHx production. The results showed that the acclimated excess sludge was able to produce PHBHHx, and the maximum output (505.6 mg/L PHBHHx containing 6.34 mol% HHx) was achieved with conditions of the continuous aeration, nitrogen and phosphorus limitation, and adequate carbon source implemented by pulse feeding 0.5 g/L sodium laurate every 4h. Moreover, composition and structure of the PHBHHx from sludge were found similar to that from pure culture, according to literature, FTIR and NMR spectra. Finally, high-throughput sequencing technique characterized that phylum Chlorobi and genus Leadbetterella should be critical groups for PHBHHx synthesis in the sludge community.

Plant-mediated synthesis of platinum nanoparticles and its bioreductive mechanism.

Pt nanoparticles (PtNPs) were biologically synthesized by reducing Na2PtCl4 with Cacumen Platycladi Extract (CPE). The effects of reaction temperature, initial Pt(II) concentration, and CPE percentage on Pt(II) conversion and the size distribution of the PtNPs were studied. The results showed that the Pt(II) conversion rate reached 95.9% and that PtNPs measuring 2.4±0.8nm were obtained under the following conditions: reaction temperature, 90°C; CPE percentage, 70%; initial Pt(II) concentration, 0.5mM; reaction time, 25h. In addition, the bioreduction of Pt(II) was attributed to reducing sugars and flavonoids rather than proteins. The elucidation of bioreductive mechanism of Pt(II) ions was achieved by investigating the changes that occurred in the reducing sugar, flavonoid and protein concentrations in the plant extract, leading to a good insight into the formation mechanism of such biosynthesized PtNPs.

Optimization of polyhydroxybutyrate (PHB) production by excess activated sludge and microbial community analysis.

In this study, a high value-added and biodegradable thermoplastic, polyhydroxybutyrate (PHB), was produced by excess activated sludge. The effects of the nutritional condition, aeration mode, sodium acetate concentration and initial pH value on PHB accumulation in the activated sludge were investigated. The maximum PHB content and PHB yield of 67.0% (dry cell weight) and 0.740gCODgCOD(-1) (COD: chemical oxygen demand), respectively, were attained by the sludge in the presence of 6.0gL(-1) sodium acetate, with an initial pH value of 7.0 and intermittent aeration. The analysis of the polymerase chain reaction (PCR)-denaturing gradient-gel-electrophoresis (DGGE) sequencing indicated that the microbial community of the sludge was significantly different during the process of PHB accumulation. Three PHB-accumulating microorganisms, which were affiliated with the Thauera, Dechloromonas and Competibacter lineages, were found in the excess activated sludge under different operating conditions for PHB accumulation.

Fed-batch production of a bioflocculant from Corynebacterium glutamicum.

The constant-rate fed-batch production of the polygalacturonic acid bioflocculant REA-11 was studied. A controlled sucrose-feeding strategy resulted in a slight improvement in biomass and a 7% reduction in flocculating activity compared with the batch process. When fed with a 3 g l(-1) urea solution, the flocculating activity was enhanced to 720 U ml(-1) in 36 h. High cell density (2.12 g l(-1)) and flocculating activity (820 U ml(-1)) were obtained in a 10-l fermentor by feeding with a sucrose-urea solution, with values of nearly two times and 50% higher than those of the batch process, respectively. Moreover, the residual sucrose declined to 2.4 g l(-1), and residual urea decreased to 0.03 g l(-1). Even higher flocculating activity of 920 U ml(-1) and biomass of 3.26 g l(-1) were obtained by feeding with a sucrose-urea solution in a pilot scale fermentation process, indicating the potential industrial utility of this constant-rate feeding strategy in bioflocculant production by Corynebacterium glutamicum.

The biosynthesis of palladium nanoparticles by antioxidants in Gardenia jasminoides Ellis: long lifetime nanocatalysts for p-nitrotoluene hydrogenation.

Gardenia jasminoides Ellis' water crude extract was used for the bioreduction of palladium chloride in this paper. The UV-vis spectrum, x-ray diffraction spectrum measurement, the Fourier transform infrared spectroscopy and TEM technique confirmed the formation of palladium nanoparticles and identified antioxidants including geniposide, chlorogenic acid, crocins and crocetin were reducing and stabilizing agents for synthesizing palladium nanoparticles in water crude extract. The particle size and dispersity were temperature-dependent. The particle sizes ranged from 3 to 5 nm and revealed the best dispersity at 70 degrees C. Catalytic performance of the biosynthetic Pd nanoparticles with good dispersity was investigated by hydrogenation of p-nitrotoluene. The catalysts showed a conversion of 100% under conditions of 5 MPa, 150 degrees C for 2 h. The selectivity of p-methyl-cyclohexylamine achieved 26.3%. The catalyst was recycled five times with no agglomeration and maintained activity, which was attributed to the appropriate protection of the antioxidants. On the basis of the study, it appears to be a new promising biosynthetic nanocatalyst for the development of an industrial process.

A general strategy for the biosynthesis of gold nanoparticles by traditional Chinese medicines and their potential application as catalysts.

Tea time! Gold nanoparticles (GNPs) could be readily prepared by a general strategy involving the reduction of aqueous HAuCl(4) in the presence of traditional Chinese medicines (TCMs). Spheroidal and triangular gold nanoparticles were observed depending on the TCM used. The strategy exemplified the universal application of plant bioresources for the synthesis of GNPs and catalytic purposes.